Nuclear power and energy storage

Abstract

An energy generation or storage site comprises a plurality of large-bore wellbores having a diameter of 4 ft to 20 ft co-located at a common site in which one or more wellbores comprise energy generation or energy storage. Energy generation wellbores incorporate nuclear energy in the form of thermal generation units such as small modular reactors (SMRs) installed within the wellbore. One or more thermal generation units may be stacked within each energy generation wellbore. Additional wellbores of the plurality of wellbores incorporate energy storage in the form of one or more of hydrogen storage, thermal-mass energy, chemical energy, and hydraulic energy.

Description

NUCLEAR POWER AND ENERGY STORAGETECHNICAL FIELD

[0001] The invention applies to the field of clean energy generation and storage, and in particular to systems and methods for utilizing large-bore drilled wellbores for underground nuclear power generation and underground energy storage.BACKGROUND

[0002] US patent 4,851,183 describes an underground nuclear power station. Others have proposed locating nuclear reactors underground in prior art (US patent 4,851,183 and US patent 3,755,076), however no practical application has been made due to limitations in the constructability and scalability of the power station. Other current reactors are placed in shallow excavations less than 100 ft deep.

[0003] Currently, oil and gas storage primarily utilizes underground salt caverns for storing hydrocarbons, and underground reservoirs for natural gas. Clean energy technologies, driven by the intermittency of renewables, has created numerous methods for energy storage both at surface and underground. Hydrogen presents a promising option for energy storage due to its potential as an energy carrier, and current development follows oil and gas, with concepts being pursued for large-scale cavern and reservoir storage.

[0004] US Patent 11,512,812B2 describes an underground vessel for hydrogen storage (UVHS). However, the underground vessel described therein includes various limitations when considering large-bore well construction. For example, the creation of secondary containment structure is not practicable, as the pipe-in-pipe vessel design option reduces economic feasibility by increasing the casing costs significantly. The aspect to test the vessel with demineralized water and to hydrotest to validate containment integrity is not valid for hydrogen gas containment. Sealing the bottom of the cylinder with a plug is not valid for large-bore wellbores, due to casing weight which requires a sealed bottom and partial air floatation during installation. The implications of gas pressure storage on wellbore design are not considered as operating pressure ranges are not defined in the invention.Furthermore, there is no consideration to the utility of the wellbore design for nuclear power generation. Similarly, prior art for underground nuclear power does not consider the utility of the wellbore for energy storage.SUMMARY

[0005] There is provided an energy generation or storage site in which plural wellbores are co-located at a common site, the plural wellbores including plural energy generation wells each containing a thermal generation unit, plural energy storage wells each storing energy, or the plural wellbores including at least one energy generation well and at least one energy storage well.

[0006] In various embodiments, the energy generation or storage site may further comprise one or more of the following features: the plural wellbores include at least one energy generation well and at least one energy storage well, and the energy storage well stores energy produced by the energy generation well; the energy storage well comprises hydrogen storage, the hydrogen being produced using energy from the nuclear well; the energy storage well provides blackstart capability to the energy generation well; the plural wellbores are each between 4 feet and 20 feet in diameter; the plural wellbores are each between 100 and 10000 feet deep; each wellbore contains a respective casing string having a pre-installed sealed bottom-end cap of the respective casing string, the nuclear reactor or energy storage occurring within the respective casing string; each wellbore further comprises a respective surface casing extending to a depth below a maximum groundwater level depth at the energy generation or storage site; hydrogen gas is injected at pressures below 5000 psi; the hydrogen gas is injected into the hydrogen storage directly at production pressure; the plural wellbores are co-located at a common site are located at an industrial site or infrastructure to provide energy generation and storage for the industrial site or infrastructure; a heated coolant from the at least one energy generation well is conveyed to the industrial site or infrastructure for use in an industrial process; the thermal generation unit comprises a nuclear reactor; the thermal generation unit comprises a SMR.

[0007] There is provided a method of construction of a wellbore for power storage or energy storage, the method comprising: drilling a borehole; providing a casing having asealed bottom end; assembling and sealing individual joints of the casing and lowering the casing assembly including the sealed bottom end into the borehole; and, sealing a cap to a top end of the casing, the cap including an inlet port for flow into the wellbore and an outlet port for flow out of the wellbore.

[0008] In various embodiments, the method may include one or more of the following features; the wellbore has a diameter sized using optimization calculus to determine a borehole diameter and casing diameter which maximizes the energy storage capacity of the wellbore; the wellbore diameters of the hydrogen storage is calculated according to:Brrr) and,

[0009] based on a target mass of hydrogen for storage for the energy generation or storage site, where m is a mass of hydrogen in grams, CUVH2 is the vessel specific constant for hydrogen storage, T is temperature in Kelvin, RH2 is a gas specific constant in Joules / (g*K), fymin is a specified minimum yield strength of the vessel casing in pascals, t is vessel wall thickness in meters, r is hole radius in m which is equivalent to half the casing diameter, and A and B are drilling equipment specific independent constants; the casing is filled in use of the wellbore with an energy storage medium; the wellbore contains in use of the wellbore a thermal generation unit for power generation; the step of installing a surface casing in an upper portion of the borehole before the step of lowering the casing having a sealed bottom, and the method further comprising the step of forming a sealing connection between the surface casing and the casing having a sealed bottom after the step of lowering the casing including the sealed bottom; the borehole is 4 feet to 20 feet in diameter; a step of installing an inlet tube connecting to the inlet port and an outlet tube connecting to the outlet port, and installing a packer within the casing having the sealed bottom, the inlet tube and the outlet tube extending below the packer; the packer is below an expected cratering depth in the event of a surface accident; the inlet tube extends to a greater depth than the outlet tube; the cap comprises one or more additional sealed ports for monitoring of the wellboreand controlling downhole equipment; the one or more additional sealed ports comprises one or more ports for conduit tubes, control lines, and instrumentation cables to monitor and control downhole equipment.

[0010] There is provided an energy generation facility comprising a first borehole having a casing, a thermal generation unit within the borehole, a first coolant loop within the borehole for extracting heat from the thermal generation unit, a heat exchanger within the borehole connected to exchange heat between the first coolant loop and a second coolant loop to cause heating or boiling of a second coolant within the second coolant loop to create a heated gas or vapour, and power generation equipment connected to receive the heated gas or vapour from the second coolant loop, extract energy from the heated gas or vapour, and return the gas or vapour to the second coolant loop within the borehole at least partially in vapour or liquid form, the gas or vapour recondensing within the borehole under passive heat transfer between the casing of the borehole and surrounding material.

[0011] In various embodiments an energy generation facility may comprise one or more of the following features: the second coolant loop comprises an outlet tube for carrying the second coolant from the heat exchanger to the turbine and an inlet tube for carrying the second coolant from the turbine to the heat exchanger, the borehole containing an additional volume around the outlet tube and the inlet tube, the additional volume containing a fluid for conductive and convective heat transfer between the inlet tube and the casing of the borehole; the circulation rate of the second coolant within the second coolant loop is maintained by a hydrostatic U-tube effect between the outlet tube and inlet tube that occurs under normal operation without a pump; the wellbore has a volume capacity that allows a sufficient liquid volume within the casing to provide reactor cooling in a shut-down or emergency scenario naturally and without a pump; a surface-powered downhole pump for causing increased circulation within the first coolant loop; a circumferential vibration dampener damper element containing an elastomeric material which is located between the casing and the thermal generation unit, and which seismically isolates the nuclear reactor; the outlet tube is dual walled; the second coolant system comprises multiple inlet and outlet tubes; a thermal expansion joint between the inlet tube and the heat exchanger to account for differences in thermal expansion between the outlet tube and the inlet tube; the thermalexpansion joint comprises a seal-stack and polished bore receptacle connecting the inlet tube to the heat exchanger.

[0012] There is provided an energy generation facility comprising a borehole having one or more casings, plural thermal generation units within the borehole, a first coolant loop within the borehole for extracting heat from the plural thermal generation units, and a heat exchanger within the borehole and connected to exchange heat between the first coolant loop and a second coolant loop, the second coolant loop conveying heat from the heat exchanger to power generation equipment located inside or outside the borehole.

[0013] In various embodiments, the energy generation facility comprises one or more of the following features: the first coolant loop connects each of the plural thermal generation units in series at least in one of an upwards direction of flow and a downwards direction of flow; the first coolant loop connects each of the plural thermal generation units in series in both the upwards direction of flow and the downwards direction of flow; the downwards direction of flow between each successive pair of thermal generation unit occurs within a respective annulus surrounding a respective pipe containing the corresponding upwards direction of flow; the plural thermal generation units, the heat exchanger, and tubes of the second coolant loop are vertically connected and weight-bearing with a vertical degree of freedom to move up or down, to form a chain and to carry a load comprising a buoyancy- corrected weight of the chain and where the tubes of the second coolant loop are anchored in a containment cap at a surface end of the borehole which transfers the load through the containment cap to the one or more casings; maintenance and refueling occurs by retrieving the tubes of the second coolant loop, to which the plural thermal generation units and heat exchanger are connected; each of the plural thermal generation units is removably connected to the chain for separate removal and replacement during maintenance or refueling.

[0014] These and other aspects of the device and method are set out in the claims.BRIEF DESCRIPTION OF THE FIGURES

[0015] Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:

[0016] Fig. 1 shows a schematic view of an embodiment of a nuclear energy generation and hydrogen storage site.

[0017] Fig. 1A shows a schematic view of an embodiment of the energy generation wellbores for energy generation using nuclear power and energy storage using hydrogen.

[0018] Fig. IB shows a schematic view of an embodiment of the overall nuclear energy generation and hydrogen storage site, showing surface facility equipment and both on-site and off-site tie-ins for energy generation and energy storage.

[0019] Fig. 2 shows a flow chart of an overview of the nuclear energy generation and hydrogen storage site construction process, including the high-level process for creating the wellbore containment structure.

[0020] Fig. 3 shows a schematic view of an embodiment of a high-temperature gas- cooled reactor (HTGR) configured to operate within a nuclear energy generation wellbore.

[0021] Fig. 3 A shows a top cross-sectional view of part of an embodiment of a nuclear energy generation wellbore taken through the line A-A in Fig. 3.

[0022] Fig. 3B shows a side section view of an embodiment of a SMR within a nuclear energy generation wellbore.

[0023] Fig. 4 shows a flow chart of a method for determining downhole hydrostatic pressure within the wellbore.

[0024] Fig. 5 is a schematic view of an embodiment of U-Tube Piping displaying the circulation path of secondary coolant.

[0025] Fig. 6 shows a flow chart of a method for determining pressure loss within the U-Tube piping embodiment shown in Fig. 5.

[0026] Fig. 7 shows a flow chart of an exemplary method of identifying the contributions to pressure within the system shown in Fig. 5.

[0027] Fig. 8 shows a schematic of an embodiment of the flow paths of working fluids (primary coolant and secondary coolant) within the Heat Exchanger Module section shown in Figure 5. The heat exchanger module also may contain a primary coolant pump (not shown in Figure).

[0028] Fig. 9 shows a flow chart of an exemplary method for determining the thermal losses within the upper wellbore U-tube coolant piping as shown in Fig. 5.

[0029] Fig. 10 shows a schematic of heat transfer resistances within the upper wellbore U-tube coolant piping as shown in Fig. 5.

[0030] Fig. 11 shows a partial side section view of the upper wellbore in an embodiment where it functions as a condenser.

[0031] Fig. 12 shows side view of embodiments of a Heat Exchanger Module with a polished bore receptacle and seal stack to accommodate difference in thermal expansion in various states of thermal operation.

[0032] Fig. 13 shows a flow chart of a method for validating the Coolant Pool function of a nuclear energy generation wellbore by comparing the pool volume capacity to that of an example reactor.

[0033] Fig. 14 shows a schematic view of an embodiment of the radionuclide boundaries between source and the environment for a generic nuclear reactor operating in an energy generation wellbore.

[0034] Fig. 15 is a diagram showing a side view of an embodiment of the nuclear energy generation wellbore with multiple SMR or thermal generation modules.

[0035] Fig. 16 is a diagram showing a side view of an embodiment of a hydrogen storage wellbore which utilizes the same large-bore drilling equipment and similar casing scheme as in the nuclear wellbore shown in Fig. 15.

[0036] Fig. 17 shows a partial side section view of an embodiment of a casing head housing which seals the wellbore at surface or seabed.

[0037] Fig. 18 shows a partial side section view of an embodiment of a casing head housing which includes a surface casing spool.

[0038] Fig. 19 shows a schematic side section view of an embodiment of a nuclear generation well containing power generation equipment inside the wellbore.

[0039] Fig. 20 shows a schematic top view of a wellhead containment cap with multiple inlet and outlet ports.

[0040] Fig. 21 shows a flow chart of a method of construction of a wellbore 102 for power generation or energy storage.DETAILED DESCRIPTION

[0041] There is provided a novel energy facility design that utilizes large-bore wellbores for both power generation and energy storage. This approach can be used at new or existing sites, for example industrial sites, and addresses current challenges in scalable power deployment by providing a cost-effective containment solution for small modular reactors (SMRs).

[0042] Large-bore drilling is the method for creating boreholes between 4 ft and 20 ft diameter. Wellbores differ from boreholes and shafts; they are lined with cylindrical pipe segments and contain pressurized fluids (gas or liquids). Large-bore drilling, pioneered at the Nevada National Test Site (NNTS) for nuclear testing, has evolved in modern times to offer potential applications in the energy sector. Advancements in multi-well pad drilling technology, including walking rigs, top drives, automated pipe handling and drilling systems, and bit design have made it practicable to construct multiple large-bore wells efficiently. Advancements in wellbore technology, including sensors, robotics, and materials science (metallurgy and composites), have made it practicable to operate, monitor, and maintain underground reactors remotely. While the number of large-bore wells drilled globally has remained relatively low (estimated at less than 1000 globally), the technology has benefited from advancements in the oil and gas, mining, geothermal, and civil industries.

[0043] Small Modular Reactors (SMRs): SMRs are classified as nuclear reactors with a power output less than 300 mega-watts (MW) electric per module. They represent a growing field with over 50 designs in development globally ranging between Technology Readiness Level (TRL) 3-9. SMRs using Generation III and IV reactor systems offer advantages such as passive (i.e. automatic or intrinsic) safety features, remote operation, and extended operational lifespans with reduced refueling requirements making them practicable for underground deployment. The deployment of existing SMRs has faced challenges, specifically the construction of surface containment structures and operating buildings which struggles to provide an economic and scalable solution to deploying SMRs due to the size, cost, complexity, and extended timelines. Additionally, a limited number of test sites is creating a backlog for testing new reactors, hindering commercialization.

[0044] An energy generation or storage site 100 comprises a plurality of wellbores 102 co-located at a common site. By locating reactor vessels, heat exchangers, and safetyfeatures within a wellbore, a nuclear energy generation wellbore eliminates the need for expensive surface containment structures and minimizes ground-level radiation hazards. Additionally, the facility's optional co-located wellbore hydrogen energy storage solution offers a safe and efficient means of storing hydrogen produced onsite or offsite, supporting the transition to a hydrogen-based energy system. As an integrated system, it further enhances the facility's economic viability. The construction of multiple containment structures at a single site offers significant cost advantages. Utilizing a single drilling rig and multi-well pad drilling reduces the unit cost per containment structure. Furthermore, the vertical, in-series arrangement of multiple reactors within a wellbore, coupled with the replication of this configuration across multiple wellbores at the site, yields additional unit cost reductions for both the containment structures and the deployed Small Modular Reactor (SMR) technology. This approach leverages factory production and replication efficiencies, leading to substantial overall cost savings. The energy generation and storage site concept represents a significant advancement in the nuclear power and hydrogen storage sectors, with the potential to accelerate the adoption of these technologies in the pursuit of global decarbonization goals.

[0045] In this text, energy generation wells are described which use containerized thermal generating units such as units employing internal nuclear reactions (fusion or fission) to generate useful heat. Such units are generally referred to as thermal generation units (TGUs). TGUs include, and are not limited to, nuclear reactors and SMR technology. Whereas various embodiments in this specification describe the use of specific types of TGUs (such as SMRs), various types and configurations may be used without loss of generality.

[0046] Energy generation or storage sites 100 are a novel energy facility concept that utilizes large-bore wellbores as sealed containment structures for nuclear power generation and underground energy storage. Unlike traditional wellbores that rely on interactions with the surrounding subsurface, the site’s fully sealed design prevents fluid exchange between the wellbore and the geological environment. This enables greater flexibility in location selection and enhances the safety and scalability of nuclear power and hydrogen storage. By co-locating energy generation wells, e.g. nuclear wells 104, containing a TGU such asnuclear reactor 106 alongside energy storage wells 108 on the same site, the energy generation or storage site 100 offers improved reliability, economic efficiency, and a more robust infrastructure for supporting the transition to a hydrogen-based energy system. The sites may utilize one or more wellbores 102, and include nuclear wells 104, energy storage wells 108, or wellbores containing one or multiple forms of underground energy storage in fluid form, such as thermal, chemical, or hydro-power, or a combination thereof. The sites may also feature surface facilities for generating or storing clean power, which may include power generation turbines 172, for example steam turbines, hydrogen electrolysers such as in an electrolyzer facility 178, operational buildings and control rooms, and electrical utilities, or a combination thereof. Due to the small footprint of the wellbore, the sites may be located at existing commercial, industrial, or residential sites and integrated with existing surface facilities.

[0047] In an embodiment as shown in Fig. 1, 1A, and IB, there is an energy generation or storage site 100 comprising plural wellbores 102 co-located at a common site. The plural wellbores 102 may include plural energy generation wells, such as nuclear wells 104 each containing a thermal generation unit, e.g. nuclear reactor 106, plural energy storage wells 108 each storing energy, or the plural wellbores including at least one nuclear well 104 and at least one energy storage well 108.

[0048] The plural wellbores 102 may include at least one nuclear well 104 and at least one energy storage well 108, and the energy storage well storing energy produced by the nuclear well 104. Further, the energy storage well 108 may comprise hydrogen storage 110, the hydrogen being produced using energy from the nuclear well. The plural wellbores may each be between 4 feet and 20 feet in diameter. The plural wellbores may be each between 100 and 10,000 feet deep.

[0049] In an embodiment, the plural wellbores co-located at a common site may be located at an industrial site or infrastructure to provide energy generation and storage for the industrial site or infrastructure. Heated coolant from at least one nuclear well 104 may be conveyed to the industrial site or infrastructure for use in an industrial process.

[0050] An embodiment of a site is shown in Fig. 1 and detailed in Fig. 1 A and IB, which comprises:

[0051] A large-bore (4 ft to 20 ft diameter) drilled wellbore with a depth between 100 ft and 10,000 ft, with an outer casing serving as the primary containment structure. A multi-well pad drilling technique enables efficient construction of multiple wellbores at a single site, reducing the cost per unit and offering scalability in power generation and storage capacity.

[0052] Energy Generation Well:

[0053] In an energy generation well such as the depicted nuclear well 104, the wellbore 102 houses one or more thermal generation units, e.g. nuclear reactors 106, such as SMRs, integrating the reactor vessel, heat exchanger, and safety features within the wellbore itself. To help validate the 50+ new reactor designs in early phases of development the nuclear wells can be configured to be utilized as a demonstration or test dome for new commercial, or research level reactors. Advancements in SMR technology, enables the nuclear well concept by including containerized reactor vessels, encapsulated fuels, and radiation-transparent coolants, or a combination thereof. Locating additional radionuclide containment boundaries within the wellbore to create an underground nuclear island eliminates the need for fast-closure mechanisms.

[0054] In an embodiment, the energy storage well 108 houses and stores large volumes of hydrogen gas at low pressure, as illustrated in Figs. 1, 1A and IB. The wellbore 102 functions as a sealed vessel which can store medium-scale (5 - 250 tonne) quantities of hydrogen gas. Limited options exist for medium-scale storage vessels (5 tonne to 250 tonne per unit) which are needed to supports the growing development of hydrogen infrastructure. Storage of hydrogen in an underground wellbore requires consideration for the containment structure to be gas-tight and avoid hydrogen embrittlement.

[0055] In an embodiment, the wellbore houses one or multiple forms of underground energy storage in fluid form, such as thermal, chemical, or hydro-power. This utilizes the same large-bore outer wellbore containment structure.

[0056] In an embodiment, the surface facilities may comprise power plants 144 such as power generation turbine 172 that will convert the heat from the nuclear well configuration into electricity or process heat. Hydrogen electrolysers such as in an electrolyzer facility 178 may also be integrated on-site, which utilize electricity to separatewater or steam into hydrogen and oxygen, with excess hydrogen being stored underground in the energy storage well configuration. This integration provides a flexible and energy efficient system.

[0057] As illustrated in Fig. 1, a representative embodiment of an energy generation and storage site comprises a plurality of wellbores 102. One or more of the plurality of wellbores 102 comprise nuclear wells 104. One or more of the plurality of wellbores 102 comprise energy storage wells 108. In various embodiments, steam produced by the nuclear wells 104 is directed by a steam header 170 to a power generator 172, e.g. a steam power facility. Water is returned from the power generator 172 via a water header 174. Electrical energy generated at the steam power facility may be transmitted to contribute to the electrical grid 176. Alternatively, or additionally, to the transmission of power to the grid, electrical energy may be transmitted to an electrolyzer facility 178. The electrolyzer facility 178 can also receive electrical energy from other power sources 180, including renewable power sources and the electrical grid. Hydrogen generated at the electrolyzer facility 178 can be directed into energy storage wells 108, such as hydrogen storage wells 110. Hydrogen may also be directed, directly from the electrolyzer facility 178, or as an outlet of the hydrogen storage wells 110, to a hydrogen output 182. Hydrogen output 182 may comprise hydrogen transport infrastructure or direct hydrogen use. Steam from the steam header 170 can also be directed to offsite industrial processes 184 requiring heat or steam.

[0058] Fig. 1 A illustrates a schematic embodiment of the nuclear wellbores 104 for energy generation and energy storage using hydrogen.

[0059] Fig. IB shows an embodiment of a energy generation and storage site 100 showing facility equipment and on-site and off-site tie ins. Steam from steam header 170 is directed to power generation turbine 172 as well as to offsite industrial processes 184, blue hydrogen production 186, and / or thermal energy recovery 188. The blue hydrogen production and thermal energy recovery processes can also include carbon capture, utilization, and storage (CCUS) technology.

[0060] In this embodiment, water for the electrolyzer facility 178 is provided from an off-site water utility 173, though various sources of water could be employed. Off-site water utility 173 may provide water for both electrolysis and steam power generation. Hydrogenfrom the electrolyzer facility 178 is directed to hydrogen wells 110. Hydrogen from the electrolyzer facility 178 and from the outlets of the hydrogen wells 110 can be directed by a hydrogen header 194. Hydrogen from the hydrogen header 194 can be directed to hydrogen fuel cells 192 for converting hydrogen to electrical energy. The electrical energy from hydrogen fuel cells 192, from the power generation turbine 172, from the electrical grid 176, and / or from the other power sources 180 can be used in on-site utility power 190. Hydrogen outputs 182 can include hydrogen direct use on-site 182A (such as fueling) or the provision of hydrogen off-site through hydrogen infrastructure 182B (such as a hydrogen pipeline).

[0061] As described elsewhere herein, additional energy storage wells 108 can be used to store other forms of energy, where “X” refers to the variable energy storage type, including thermal, electrical or chemical energy. Process headers 196 can be employed to direct the appropriate energy into energy storage wells 108 from energy-X inputs 198 and out of the energy storage wells 108 to energy-X outputs 199.Wellbore Construction

[0062] The nuclear well 104 and energy storage well 108 wellbore containment systems may be the large-bore wellbore, which serves as the primary containment structure. This section details the construction process 200 of the wellbore 102, as shown in Fig. 2, highlighting key steps and considerations.

[0063] The wellbore 102 may comprise a borehole (hole in the earth) that is converted into a wellbore once fully encased and tested as a fluid-competent structure fit for its intended purpose. The wellbore containment structure is pressure-sealing and hydrostatically competent to both internal and external pressures, which differentiates it from a shaft. Some modifications to each structure are required for the specific energy application. Site Selection and Preparation

[0064] The first step in wellbore construction involves careful site selection and preparation 210. The chosen site does not require specific geological and environmental criteria, however the preparation must ensure the borehole can be drilled successfully and the surrounding subsurface is suitable for the wellbore's long-term integrity and safety. The wellbore and site locations may be both onshore and offshore.

[0065] Geological Assessment: A geological assessment is conducted to evaluate the subsurface formations, including their strength, permeability, offset wells, and seismic activity.

[0066] Environmental Impact Assessment: An environmental impact assessment is performed to identify and mitigate any potential environmental impacts associated with the wellbore construction and operation.

[0067] Site Preparation: The chosen site is cleared and prepared for drilling operations, including access road construction, equipment staging areas, and necessary infrastructure.

[0068] Subsurface Preparation 220

[0069] It may be necessary to prepare the subsurface using a grouting program which limits fluid movement into or away from the borehole during drilling. A number of smaller boreholes are drilled around the wellbore and cement or grout is squeezed into the formation 320 to encircle the main borehole. It may also be necessary to drill a smaller pilot hole at the main borehole location.

[0070] Surface Drilling and Casing

[0071] In an embodiment as shown in Fig. 21, there may be a method of construction of a wellbore 102 for power storage or energy storage. The method may comprise drilling a borehole 120 in step 510, providing a casing 112 having a sealed bottom end 520 at step 520, assembling and sealing individual joints of the casing 112 and lowering the casing assembly 112B including the sealed bottom end into the borehole in step 530, and sealing a cap 122 to a top end of the casing in step 540, the cap may include an inlet port 124 for flow into the wellbore and an outlet port 126 for flow out of the wellbore 102. In an embodiment, the casing 112 may be filled in use of the wellbore with an energy storage medium. A surface casing 116 may be installed in an upper portion of the borehole before the step of lowering the casing having a sealed bottom, and the method may further comprise the step of forming a sealing connection between the surface casing 116 and the casing having a sealed bottom after the step of lowering the casing including the sealed bottom.

[0072] In some embodiments, there may be installed an inlet tube 128 connecting to the inlet port 124 and an outlet tube 130 connecting to the outlet port 126, and installed apacker 132 within the casing 112 having the sealed bottom, the inlet tube and the outlet tube extending below the packer 132. The packer may be below an expected cratering depth in the event of a surface accident. The inlet tube may extend to a greater depth than the outlet tube. The cap may include one or more additional sealed ports 134 for monitoring of the wellbore.

[0073] To isolate shallow unstable zones and provide structural support for the wellhead and casing vessel, a conductor pipe 164, surface casing 116, cement support ring, or combination thereof are installed. In an embodiment, a shallow cellar 166 is first created to help collect cement returns from conductor and surface cementing, and to facilitate positioning the wellhead and tree valves at suitable elevations. The surface drilling and casing, comprising the shallow cellar 166, conductor 164, and a surface casing 116 is made using auguring, piling, rotary drilling, or excavation units, or a combination thereof. Conductor and surface casings may include an annular grout / cement 318 to provide fluid isolation for drilling the next section and to support the axial load of the casing vessel, wellhead and tree. According to one aspect of some embodiments, a surface casing is installed to a depth across shallow formations which may contain groundwater or shallow aquifers. In an embodiment, each wellbore 102 may comprise a respective surface casing extending to a depth below a maximum groundwater level depth at the energy generation or storage site 100. In another aspect of some embodiments, the surface casing or an additional casing strings or liners (casing hung-off in previous casing and not connected back to surface) may be used to case off intermediate unstable zones. The casing may be at least partially filled with a liquid or a slurry as it is lowered into the borehole to reduce buoyancy.

[0074] Large-Bore Drilling 230

[0075] In an embodiment, the borehole may be 4 feet to 20 feet in diameter. The main borehole for the wellbore 102 is drilled using large-bore drilling equipment capable of creating holes with diameters ranging from 4 ft to 20 ft. This differs from conventional rotary drilling where sizes are below 4 ft diameter. Suitable equipment for large-bore drilling the main cased hole includes heavy-duty conventional rotary rigs, shaft sinking units, blindbore shaft drilling units, or a combination thereof. In some embodiments, surface borehole drilling and casing may also employ large-bore drilling equipment, where the subsurfaceconditions require a deeper installation. The borehole can be drilled to a depth between 100 ft and 10,000 ft, with a diameter selected based on the wellbore application and optimal wellbore casing size as described herein.

[0076] Some embodiments utilise blind-bore shaft drilling units, which are designed to reach the large-bore diameters and intended depths. In another aspect of some embodiments, modified conventional rotary rigs are utilized. The specific drilling method will vary depending on the available equipment, site conditions (surface and subsurface), and the specific wellbore applications.

[0077] Blind-Bore Drilling: This method involves shaft drilling units drilling a pilot hole or full-bore hole from surface, which may be followed by reaming to the final diameter, offering precise control and minimal disturbance to the surrounding formations.

[0078] Heavy-Duty Conventional Drilling: Traditional rotary drilling using heavy- duty conventional rigs with 250 ton or greater hookload can also be employed. Heavy-duty conventional drilling rigs equipped walking systems, top drives, and automated pipe handling are preferred for multi-well pad drilling efficiency.

[0079] Multi-Well Pad Drilling: For sites with multiple wellbores, multi-well pad drilling techniques utilise rigs which can walk or skid between wells, is used to improve efficiency and reduce costs. Drilling bottom-hole assembly design, anticollision monitoring, and borehole surveying methods are used to accurately place wellbores in close proximity.

[0080] Offshore Drilling: For offshore sites, large-bore offshore drilling equipment can be utilized from vessels, jackups, or platforms, or any type of offshore drilling equipment. Surface conductor / casings may be efficiently installed using subsea piling equipment such as those used for constructing subsea monopiles for offshore platforms or wind-turbines. For offshore sites, the wellbore containment of energy generation and storage puts the loads on the seabed and shallow formations, which also reduces the overall footprint, weight and cost of associated offshore structures.

[0081] Casing, Wellhead, and Cementing 240

[0082] In an embodiment, the wellbore 102 may comprise a casing string comprising one or more casings. Once the borehole is drilled to the desired depth, multiple layers of casing 112, which may comprise steel or other appropriate material, are installed to providestructural support and isolate the wellbore from the surrounding formations 320. In various embodiments, pressure is fully supported by the casing walls and the design does not rely on external annular cement 318 or formation strength to support the internal vessel pressure during operation.

[0083] As shown in Fig. 17, an outer casing string is first installed as the support for the casing head housing. In the configuration in Fig. 17, the casing vessel connects directly to the casing head housing and lands off on the outer conductor pipe. In this configuration, the Xmas Tree attaches directly to the casing head housing.

[0084] In another configuration, as shown in Fig. 18, two outer casing strings (first a shallow conductor and then surface casing) are installed. The surface casing connects to the casing head housing and lands off on the outer conductor pipe. The casing vessel connects to the casing head spool, and lands off on the casing head housing. The Xmas Tree attaches to the casing head spool.

[0085] Inclusion of a casing string and accompanying casing head spool may depend on local subsurface risks and regulatory considerations.

[0086] An outer casing string is first conveyed into the wellbore and cemented to surface. The next sections are then drilled, and the final casing is cemented to below the previous casing shoe, into the previous casing shoe(s), or to surface, depending on annular isolation requirements and annular pressure management.

[0087] The casing may comprise a primary containment casing 112, also referred to as the casing vessel, that is installed within the deepest section of the borehole. The casing vessel has a pre-installed vessel head or casing shoe at the bottom to assist with running in hole. Due to casing weights, a technique called casing floatation may be used to reduce the running hookload.

[0088] Casing Selection: The casing material is carefully chosen based on the specific application, such as a nuclear well or energy storage well, and anticipated operating conditions.

[0089] Connection Selection: Pipes are joined using mechanical types of threaded connectors or welding. Connections must be leak-tight and able to withstand design loads for the desired application.

[0090] Casing Design: Factors such as strength, corrosion resistance, temperature resistance, and fatigue life are considered in the design and selection of casings. A key limitation in design of large-bore wellbores compared to smaller wellbores is collapse design. Deeper sections of the casing vessel require external stiffening rings. External stiffening rings provide structural support for hydrostatic collapse pressures for large- diameter pipes due to the reduced buckling resistance in pipes with large diameter to wall thickness ratios. Design theory may follow the Bryant Theory of Elastic Collapse, as shown in the equation below.Moment of interia of frame and one frame space of shell plating

[0099] R = Mean shell radius

[0100] Lf = Center — to — center frame spacing

[0101] Casing Installation:

[0102] Multiple cylindrical pipe segments referred to as casing joints are installed to ensure structural integrity of the wellbore. The casing sections are lowered into the wellbore and connected using mechanical couplings or welding. Centralizers are used to ensure the casing is properly centered within the wellbore. The casing string(s) is / are landed at surface into a casing head housing (Fig. 17, Fig. 18) as part of the surface containment wellhead. In one embodiment where an outer surface casing is installed (Fig. 18) in the casing head housing, a casing head spool is also installed to anchor the inner casing vessel.

[0103] The casing may provide a single-wall barrier design, similar to that utilized in pressure vessels, and including the shallow surface casing option may act as a secondary containment barrier.

[0104] In an embodiment, a sealed vessel bottom may be run and the casing may be filled partially to overcome buoyancy using a method referred to as casing flotation. This improves prior art by removing the need for the bottom assembly and improves the method to pump primary cementing using a packer, which is not practicable for large-bore sizes.

[0105] In an embodiment, each wellbore may contain a respective casing string having a pre-installed sealed bottom-end cap 114 of the respective casing string, and the nuclear reactor or energy storage may occur within the respective casing string. In various embodiments, the surface casing may extend to a depth that is below a maximum groundwater level depth at the energy generation or storage site.

[0106] Containment Cap: The containment cap 162 seals the wellbore at surface and provides conduits for flow into and out of the well, and for monitoring and operating downhole equipment. It includes two main components, the Wellhead and Xmas Tree.

[0107] Wellhead: The wellhead may include a casing head housing 452, casing head spool 454, side outlet valves 456, as shown in Figs. 17 and 18. Annulus monitoring elements may be installed into the wellhead components to monitor conditions in the wellbore. Additionally, the wellhead includes seals and test ports to provide a verifiable secure and pressure-tight connection between the wellbore casing and the surface equipment. Additional ports may also be included to facilitate cables or wires for downhole monitoring or control instrumentation. The wellhead is installed as the final step of the casing installation. The casing head housing is integrally connected to the uppermost casing joint and provides the attachment for the next spool. When configured with a surface casing string, it provides a landing shoulder for the next casing as well as a top attachment for the casing head spool which connects the Xmas Tree. The casing head housing and spool and are designed to be pressure-tight, with metal-to-metal sealing capabilities.

[0108] The Xmas trees may comprise various valves, spools, gauges and chokes, including flow wing valves, upper and lower master valves, the tubing hanger, additionalcasing hangers, and one or more control lines. The Xmas tree may include a multi-tree tubing spool 450, control cables and / or monitoring gauges 458, and Xmas tree valves 460.

[0109] Cementing: The annulus between the casing and borehole wall is cemented in stages using a small pipe or tremie pipe conveyed into the annular gap. Cement slurry is pumped into the annulus between the casing and the wellbore wall. The cement provides additional structural support, wellbore stability, prevents fluid migration in subsurface zones, and facilitates future abandonment. The cement blend is tailored to be applicable to the design requirements and regulatory requirements of the configuration. In some configurations, fluids, resins, or alternative cementing materials may be utilized in combination of, or in replacement of annular cement for the purpose of zonal isolation of surrounding formations and as part of the containment design.

[0110] Annular cement is not relied upon as a radionuclide containment boundary element in the nuclear wells 104 until verified using industry accepted practices for cement integrity logging.

[0111] Wellbore Testing and Quality Control 250

[0112] After casing and cementing, the completed wellbore undergoes rigorous testing to verify its integrity and leak tightness and to verify its ability to withstand the anticipated operational pressure and stresses.

[0113] Pressure Testing: The wellbore is filled with water, nitrogen or another suitable fluid and pressurized to a level exceeding the anticipated operating pressure. The pressure is maintained for a specified duration to ensure no leaks or deformations occur.

[0114] Cement Integrity Log: A cement integrity log may be run inside the casing or through pre-installed annular pipes to evaluate the continuity of cement and quality of the cement bond to the casing and the formation.

[0115] Other Quality Control Measures:

[0116] Additional quality control measures may be implemented, to meet any regulatory or industry standard requirements depending on the jurisdiction. Inspections such as visual inspections using downhole cameras, ultrasonic or electromagnetic sensors, gyroscopic surveys, logs, or a combination thereof may be used to verify the wellbore quality.

[0117] Configurations - Downhole Equipment and Tubing Installation 260 A,260B, 260C

[0118] The wellbore equipment is installed according to the appropriate configuration. In a given energy generation and storage site, one or more wellbore equipment and tubing installation processes are followed as applicable to the configuration of the site. In step 260A, downhole equipment and tubing in installed for energy generation wells. In step 260B, tubing is installed for hydrogen storage wells. In step 260C tubing is installed for any other applicable energy storage wells. Tubing joints (small diameter pipe, typically below 10 inch diameter) are connected to a tubing hanger and landed in a tubing spool, which is connected to the casing head housing (Fig. 17) or casing head spool (Fig. 18).

[0119] In one aspect of some embodiments, jointless tubulars are utilized as outlet tube 130 or inlet tube 128, to reduce the potential leak paths by minimising the number of connections. Small diameter pipes can be conveyed downhole efficiently using coiled tubing units.

[0120] In another aspect of some embodiments, the tubing may be internally or externally coated for insulation, friction reduction, corrosion prevention or a combination thereof.

[0121] In another aspect of some embodiments, a multi-tree tubing spool 450 is used which is novel to the wellbore configuration and is enabled by the large-bore diameter of the wellbore. This may include ports for gauges, cables or wires for downhole monitoring or control instrumentation. The tubing spool is installed before the tubing and hanger which facilitates tubing installation, retrieval, and sealing of the hanger in the tubing spool.

[0122] Xmas Tree Installation 270

[0123] The initial embodiment of the wellbore is equipped with a dual-tree tubing spool, and each tree provides leak-tight containment which facilitates access for fluid in / out, monitoring of wellbore conditions, and control of flow and integrity. This overall equipment including the wellhead and tree is referred to as the “containment cap” 162. In other embodiments, the wellbore may be a single tree with a flow path through annular space between tubing and casing instead of a separate tree.

[0124] Christmas Tree: A Christmas tree, “Xmas tree”, or “tree” is a pressure containing block and valve assembly which may include a lower master valve, upper master valve, flow block, flow wing valve, gauges, and other control equipment (chokes or emergency shutdown valves), or a combination thereof. The Christmas tree includes seals and test ports which provides a verifiable secure and pressure-tight connection between the tubing and the surface equipment. Additional ports may also be included to facilitate cables or wires for downhole monitoring or control instrumentation. In an additional configuration, the tree is an integral solid block design where the valves are within a single solid body which has a more compact body, and reduced leak paths. In yet another configuration, a subsea tree design is used for subsea operating environments.

[0125] Modular Xmas Trees: In one embodiment, the wellhead facilitates a modular number of Xmas trees to be installed on one wellbore, as appropriate to the configuration in use, between one (1) to ten (10) Xmas trees may be installed per wellhead to facilitate additional tubing strings and flow paths to the tubing, annulus, and subsurface equipment as shown in Fig. 20. In the initial embodiment, two Xmas trees are utilized as shown in Figs. 17 and 18.

[0126] Subsea Xmas Trees: For subsea environments, the subsea tree equipment has an integral body or block which encompasses multiple tubing and annulus access ports, tree, tubing and wellhead connectors, and includes remote operational equipment control panels for subsea operations into one system, as part of the containment cap 162.

[0127] Completion Equipment Tests 280

[0128] Pressure Testing: The tubing is filled with water, nitrogen or another suitable fluid and pressurized to a level exceeding the anticipated operating pressure. The pressure is maintained for a specified duration to ensure no leaks or deformations occur.

[0129] Operational Testing: Final tests and checks on any of the downhole equipment or instrumentation may occur at this point prior to commissioning the facility.

[0130] The completion of these steps results in an operational wellbore, ready for startup and commissioning in the nuclear wellbore, hydrogen storage wellbore or additional energy storage wellbore configurations, or a combination thereof. The robust design and construction of the wellbore containment system ensure its long-term stability, safety, andfunctionality in providing a versatile platform for energy generation and storage. Depending upon the configuration of the energy generation or storage facility, additional steps may be taken to tie-in facility processes 290 with other on-site or off-site processes, such as connections for providing steam to off-site industrial processes.Nuclear Configurations

[0131] In an embodiment, the wellbore may contain in use of the wellbore a nuclear reactor for power generation.

[0132] One embodiment or portion of the energy generation or storage wellbore is the energy generation system, which utilizes the large-bore wellbore as a containment structure for operating commercial or demonstration small modular reactor (SMR) unit(s). The design of the energy generation or storage wellbore eliminates the need for a conventional reactor containment building. The surrounding rock formations 320 provide natural shielding against radiation, and the wellbore itself serves as the primary containment structure. The large volume of fluids which may be contained in the wellbore also facilitates cooling and shielding fluids to be located around the reactor. This eliminates the significant cost and construction time associated with traditional above-ground containment buildings.

[0133] A visual representation of an initial embodiment with multiple SMR or thermal generation modules is shown in Fig. 15.

[0134] Wellbore Sizing

[0135] Wellbore diameter is selected depending on the desired power generation capacity, energy use, and type of reactor module selected. According to one aspect of some embodiments, there is provided a method of determining minimum wellbore sizing for reactor containment. A selection of industry SMR designs were analysed using the geometric buckling equation for a simple cylinder, to validate that a reactor vessel can be sized to fit within a large-bore (4 ft to 20 ft diameter) wellbore and reach criticality using low enriched fuel.

[0139] BgA2 is the geometric buckling factor,

[0140] Reis the radius,

[0141] Heis the height.

[0142] This has established a minimum cased hole inner diameter of 4 ft for the wellbore. Below a cased-hole diameter of 4 ft, it has been determined that the neutron efficiency of a reactor fuelled with low-enriched uranium (including high-assay low- enriched uranium) negatively impacts the lifetime of the fuel in the reactor, and the capital cost of the reactor. While criticality depends on reactor design and fuel properties, this analysis demonstrates that large-bore drilling capabilities are essential for the practical containment of SMRs when placed in an underground configuration.

[0143] The initial embodiment is a 10 ft inner diameter cased-hole wellbore, within a 12 ft drilled borehole. This size is compatible with various SMR designs being developed by the nuclear industry and can reach a depth of 1500 ft or more, using both blind-bore shaft drilling units or heavy-duty conventional rigs. Studies in the 1970’s have shown it is feasible to reach 6,000 ft true vertical depth (TVD) in large-bore sizes, and with modem rigs and materials it is reasonable to assume a technical limit of 10,000 ft TVD is now possible.

[0144] The wellbore containment structure functions as a shielded compact housing for a single or multiple small modular reactors (SMR) connected in series. This integrated system incorporates the reactor vessel(s), heat exchanger, and enables remote operation and safe management of fuel, enhancing safety at a lower cost. The nuclear island is located deep underground, and containment boundaries within the wellbore allow the entire nuclear facility to be located within the wellbore, removing the need for additional containment or shielding structures around the wellhead at surface, as well as reactor safety features which create boundaries within the well and remove the requirement for explosive closure and mechanical valves emplaced along the hole.

[0145] Wellbore Design

[0146] The energy generation or storage system incorporates design features to effectively manage pressure and thermal loads:

[0147] Secondary Coolant Loop: In one embodiment, two separate tubing strings are used for the secondary coolant loop 140, which are connected to the heat exchanger module.The inlet tube 128 returns cooler fluid to the wellbore, and the outlet tube 130 transmits heated fluid to surface and is designed to minimise the secondary coolant energy loss between the heat exchanger and surface. In the initial embodiment, the outlet pipe 130 has a dual-walled pipe design with an inner tubing 312, annular gap 310 to minimise heat loss, and outer tubing 312A. Inner production tubing 312 separates the hot leg of the secondary coolant 314 from the air in the annular gap, tubing annulus, and cooler leg of the secondary coolant 316. Inlet tube 128, carrying cooler fluid in the cooler leg of the secondary coolant 316 is illustrated with a single layer of tubing, but might in some embodiments be provided with additional insulation or an annular gap (not illustrated) to improve efficiency. The annular gap around the tubing may be in a vacuum or contain an inert gas. This configuration is detailed in Figs 3 and 3 A. In some embodiments, the outlet tube may be dual walled. In some embodiments, the second coolant system may comprise multiple inlet and outlet tubes. Inert fluid 322 such as liquid water or nitrogen or a combination thereof may occupy the space between outlet tube and inlet tube.

[0148] In another configuration with two separate strings the outlet tube is single walled and is externally coated with high-temperature insulation.

[0149] In yet another configuration, secondary coolant circulated through a single dual-walled pipe, with hot fluid moving up the inner tube, and cooled fluid returning down the annulus, or visa-versa, which also creates a U-tube effect. A single dual walled pipe configuration requires more complex design and control of the heat exchanger operation due to additional heat exchange occurring between hot and cold legs of the coolant outside of the heat exchanger.

[0150] In another configuration, coolant returns down the cased-hole annulus instead of through a separate inlet tube, which also creates a U-tube effect. However, this reduces containment boundaries compared with a dual-tubing configuration.

[0151] In various embodiments, heat from the Thermal Generation Module may be supplied by an underground SMR or other heat source. This heat may be applied to the heat exchanger and U-tube piping to create a U-tube effect as shown in Fig. 5.

[0152] In another aspect of some embodiments, the secondary coolant will operate as a closed-loop, where fluid returns from the turbine power equipment at surface are returned back into the wellbore, as shown in Fig. IB.

[0153] In yet another aspect of some embodiments, the secondary coolant is preheated by the hot coolant leaving the wellbore, to improve the heat exchanger module 138 efficiency, as shown in Fig. IB.

[0154] Thermal Loss Design: When modelling the heat circuit, it has been found that for the wellbore thermal circuit and secondary coolant loop 140 temperature losses, as shown in Fig. 9 and Fig. 10, there will be minimal temperature drop (<5%) transferring heat from the reactor to surface, which does not significantly limit the power output capacity of a reactor within the energy generation or storage wellbore embodiment. Fig. 9 is a flow chart showing a model calculation of temperature losses based on nuclear well parameters including well size, thermal conduction coefficients, and flow parameters. Fig. 10 illustrates the successive layers of thermal resistance between the secondary coolant and the rock formation. The secondary coolant 314 is contained in an inner production tubing 312 which is surrounded by an annular gap 310. The annular gap may be occupied by inert gas. Outside the annular gap is the outer tubing 312A which is surrounded by an annular volume of inert fluid 322. The volume of fluid 322 may, for example, be stagnant inhibited water. The volume of fluid is contained by outer casing 112 which is itself contained within cement 318 connecting the wellbore containment structure to the borehole wall and surrounding rock formations.

[0155] In an embodiment, there is disclosed an energy generation facility that may comprise: a first borehole 120 having a casing 112; a nuclear reactor 106 within the borehole 120; a first coolant loop 136 within the borehole for extracting heat from the nuclear reactor; a heat exchanger 138 within the borehole and connected to exchange heat between the first coolant loop 136 and a second coolant loop 140 to cause boiling of a second coolant within the second coolant loop 140 to create a gas or vapour; power generation equipment 144, 172 connected to receive the vapour from the second coolant loop 140, extract energy from the gas or vapour, and return the gas or vapour to the second coolant loop 140 within the borehole.

[0156] In an embodiment, the the gas or vapour recondenses or cools within the borehole under passive heat transfer between the inlet tube and surrounding material as shown in Fig. 11.

[0157] In an embodiment, the second coolant loop 140 may comprise an outlet tube 130 for carrying the second coolant from the heat exchanger 138 to the turbine and an inlet tube 128 for carrying the second coolant from the turbine to the heat exchanger, the borehole containing an additional volume around the outlet tube and the inlet tube, the additional volume containing a fluid for conductive and convective heat transfer between the inlet tube and the casing of the borehole. The circulation rate of the second coolant within the second coolant loop may be maintained by a hydrostatic pressure difference due to the boiling in the heat exchanger which creates a U-tube effect between the outlet tube and inlet tube that circulates the secondary coolant under normal operation and without an external pump as shown in Fig. 5.

[0158] Hydrostatic Pressure Utilization: The fluid weight due to depth of the reactor and heat exchanger modules creates a sufficient natural pressure on the heat exchanger and / or reactor coolant systems to overcome frictional losses in the pipes without any further input energy at surface to power pumps for circulating fluid. Hydrostatic pressure effect is defined as the pressure affected by the density and vertical height of a fluid column. The process for determining the bottom hole pressure is shown in Fig, 4. In step 324, it is assumed that the fluid height in the well is less than or equal to the well depth. In step 326, the density of the liquid (e.g. water) is referenced. In step 328, the pressure at the bottom of the well is calculated using the equation P = pgh where p is the density of the liquid, g is the standard acceleration due to gravity on Earth, and h is the height of the liquid column. The depth of the heat exchanger unit creates significant hydrostatic pressure which, in combination with the heat exchanger, creates natural circulation without input energy from secondary coolant pumps at surface.

[0159] In some embodiments, as the liquid coolant is converted to gas in the heat exchanger module, the lower density creates a pressure differential in the heat exchanger between the higher pressure from the hydrostatic pressure of the liquid column, and lower hydrostatic pressure from the gas column formed, due to the U-tube design of the piping.This creates a natural circulation loop, as shown in Fig. 5, which is powered by the heat output of the reactor module(s) 106 into the heat exchanger module 138.

[0160] According to one aspect of some embodiments, surface pumping equipment is not required during normal operation of both secondary coolant and turbine condenser coolant circulating loops, which increases the overall energy efficiency of the system and provides a fail-safe benefit in the event of power loss or equipment malfunction.

[0161] Passive Heat Management: According to another embodiment, the design may utilize natural convection currents within the wellbore to dissipate heat, reducing reliance on mechanical pumps.

[0162] According to another aspect, advanced reactor designs which leverage natural circulation of the primary coolant are utilized which do not require external pumps or coolant systems.

[0163] In yet another configuration, the entire wellbore is liquid-filled, and secondary coolant condensation will occur within the upper wellbore section where the geothermal temperature is coolest, as shown in Fig. 11. The turbine exhaust is routed directly back into the wellbore, and the top section of the wellbore acts as a heat sink and condenser around the inlet tube 128. This aspect uses the geothermal gradient of the earth surrounding the wellbore and convective and conductive heat transfer into the surrounding fluids and rock, either fully or partially replacing surface facility equipment such as a coolant tower, dry-gas coolant, or other type of condenser and condenser coolant pump system.

[0164] Thermal Expansion Management: The wellbore incorporates materials and design features to accommodate thermal expansion and contraction during operation.

[0165] According to one aspect of some embodiments, a sump with thermal expansion headroom is included in the initial embodiment. Thermal expansion is the elongation of components when heated, and is a known challenge for tubulars operating at high temperatures in wellbores. The initial embodiment overcomes this challenge by placing the reactor a short distance off-bottom in the cased hole and allowing the entire system within the wellbore casing to move with a vertical degree of freedom. There may be a thermal expansion joint between the inlet tube 128 and the heat exchanger 138 to account for differences in thermal expansion between the outlet tube 130 and the inlet tube 128. Thethermal expansion joint may comprise a seal-stack and polished bore receptacle 156 connecting the inlet tube to the heat exchanger. In some embodiments, the outlet tube 130 may have a thermal expansion joint (not shown) instead of or in addition to the thermal expansion joint of the inlet tube 128.

[0166] According to another aspect of some embodiments, a polished-bore receptacle (PBR) and seal-stack 156 are utilized between the heat exchanger and inlet tube, to allow for thermal expansion of the system when operating while maintaining a seal in the secondary coolant reaching the heat exchanger, as shown in Fig. 12. During thermal operation, the hot outlet tube 130 and cooler inlet tube 128 will have different amounts of thermal expansion and contraction due to the temperature difference in fluids they contain. The seal engagement length 382 is the length by which the polished bore receptacle and seal-stack 156 can adjust to account for thermal expansion. This length is prepared to account for the full range of anticipated potential temperature differences between the outlet tube and inlet tube. The outlet tube will change in length significantly more than the inlet tube due to thermal expansion, causing the seal to travel within the PBR, and maintain the seal. The tubing is fixed at surface in the tubing hanger, as shown in Fig. 17 and Fig. 18, so differences in expansion must be accounted for to prevent excessive axial stresses in the tubing and tubing hanger.

[0167] Pressure Loss Design: Pressure losses in the circulating system are integral to the design of the secondary coolant loop, heat exchanger, and largely depend on selection of tubular sizes, as shown in Fig. 6 and Fig. 7.

[0168] Fig. 6 illustrates a process for calculating various features of the pressure and flow in the circulation system. In step 330, various input parameters are retrieved, including in which Vsteamis velocity of the steam, D is the diameter of the pipe, z;nis the height of input, Zout is the height of the output, Wshaftis the height of the fluid column at the exit point of the shaft, Pin is the input pressure, and a is the pipe roughness (taken from table values). In step 332, the properties of hot secondary coolant, such as superheated steam, are calculated or retrieved from table values, including the density, p, and the dynamic viscosity of the fluid, p. In step 334, the Reynold’s number is calculated as Re =In step 336 the lengthis calculated as I = zout— zinand the friction factor is calculated. The friction factor may be calculated assuming turbulent flow or other flow regimes. In an embodiment, the friction factor is calculated as - . In step 338, the specific gravity, y iscalculated as y = pg and the head loss is calculated as hLsteP 340 thepressure at well entrance (ground level) is calculated as Pout= Pin— Yzout ~zin) ~ + Pwshaft- Fig illustrates the hydrostatic pressure of 1000 ft of water 342 isapproximately equal to the sum of the hydrostatic pressure of 1000 ft of steam 344, the frictional pressure drop in the water pipe 346, the frictional pressure loss of steam in the pipe 348, the pressure drop at the heat exchanger 350 and the pressure drop at the turbine 352. According to one aspect of some embodiments, a self-regulating flow rate of the secondary coolant is achieved by selecting pipe sizes which provide the necessary friction losses to choke the flow at the desired rate.

[0169] In another aspect of some embodiments, surface pumps, chokes in the surface piping, or a combination thereof, may be used to further control flow rates, or as backup systems in case of a downhole equipment issue.

[0170] Thermal Generation Unit Integration

[0171] The Thermal Generation Unit (TGU) 106 includes any type of containerized unit using internal nuclear reactions (fusion or fission) to generate useful heat. The general category of TGUs includes such systems as nuclear reactors. Embodiments of the TGU are designed to accommodate without limitation various SMR designs. A single wellbore can house one or more SMR modules, as shown in Fig. 19 enabling flexible power generation capacity. The SMR modules are pre-fabricated, self-contained units containing the SMR vessel structure, essential control and safety systems and equipment, and may also include a heat exchanger and pump for primary coolant. SMR(s) operating within the wellbore are monitored and inspected remotely and may be retrieved from the wellbore for maintenance, refuelling or decommissioning by removing the tubing from the well at surface, to which the heat exchanger and TGU are integrally connected.

[0172] Transportation to site: The TGU 106 height will be between 10 ft and 100 ft, and outer diameter between 4 ft and 20 ft. The initial embodiment TGU is 50 ft in height and 10 ft in diameter.

[0173] Reactor, Heat Exchanger, and Tubing Installation:

[0174] The SMR module(s) are lowered into the wellbore through a designated access opening at the top. Specialized rigging equipment ensures safe and secure module placement. Once the wellbore is tested for integrity without a TGU, the TGU module(s) 106, then heat exchanger module 138 are conveyed underground. In the initial embodiment, it is conveyed and connected using tubing connected to ground / seabed-level using a tubing hanger. The tubing functions as the coolant flow and heat removal piping. Other possible embodiments utilise braided wire rope or rods for conveyance of the TGU(s) and heat exchanger, with the tubing installed afterwards. The TGU(s) is / are suspended from the heat exchanger, which is suspended from the tubing. The tubing is suspended in the tubing hanger which transfers this load to the wellhead and casings, which are anchored to the ground. In case of seismic activity, a lateral vibration damper is included on the outside of the vessel to minimise any impact force between the reactor vessel and casing due to movement. In another embodiment, a vibration absorber is placed under the reactor. In an embodiment, there may be a circumferential vibration dampener element 152 containing an elastomeric material which is located between the casing 112 and the nuclear reactor 106, and which seismically isolates the nuclear reactor.

[0175] Vertical Integration of Reactor Modules:

[0176] In an embodiment, there may be an energy generation facility that may comprise: a borehole 120 having one or more casings 112; plural TGUs 106 within the borehole 120; a first coolant loop 136 within the borehole for extracting heat from the plural TGUs; and a heat exchanger 138 within the borehole and connected to exchange heat between the first coolant loop 136 and a second coolant loop 140, the second coolant loop conveying heat from the heat exchanger to power generation equipment 144 located inside or outside the borehole 120. The first coolant loop 136 may connect each of the plural TGUs 106 in series at least in one of an upwards direction of flow and a downwards direction of flow. The first coolant loop 136 connects each of the plural TGUs 106 in series in both theupwards direction of flow and the downwards direction of flow. The downwards direction of flow between each successive pair of TGUs 106 may occur within a respective annulus 158 surrounding a respective pipe containing the corresponding upwards direction of flow. The plural TGUs, the heat exchanger, and tubes of the second coolant loop may be vertically connected and weight-bearing with a vertical degree of freedom to move up or down, to form a chain 160 and to carry a load comprising a buoyancy-corrected weight of the chain 160 and where the tubes of the second coolant loop are anchored in a containment cap 162 at a surface end of the borehole in a tubing spool 450 which transfers the load through the containment cap 162 to the one or more casings. Maintenance and refueling may occur by retrieving the tubes of the second coolant loop 140, to which the heat exchanger 138, primary coolant loops 136, and plural TGUs 106 may be connected. Each of the plural TGUs 106 may be removably connected to the chain 160 for separate removal and replacement during maintenance or refueling.

[0177] In one aspect of some embodiments, multiple TGUs may be installed and operated in series into a single energy generation wellbore to scale up the generation capacity, or output temperature, from within a single energy generation containment structure. One energy generation wellbore may contain a single TGU or a vertically stacked series of multiple TGUs, with total power output range between 1 MW - 1000 MW electric power. This novel concept resembles a “string of pearls” of vertically integrated reactors operating in the same energy generation wellbore, as shown Fig. 15. At 10,000 ft depth, it is feasible to install up to 200 reactor modules wherein the potential combined power output is limited by either power removal capacity or decay heat removal capacity of the system. In this configuration, the length of the energy generation nuclear island section 424 is increased by drilling deeper and the heat exchanger can also be enlarged within one energy generation well to meet the required process conditions depending on the number of reactor modules. In an alternative embodiment multiple heat exchangers may be installed to facilitate higher power outputs.

[0178] In Fig. 15, the nuclear island 424 is a considerable distance below surface level 418 and beneath both the deepest ground water level 422 (which varies by location)and the surface accident cratering depth 420. In this design, all of the multiple TGUs per wellbore are beneath the deepest ground water level 422 and the cratering depth 420.

[0179] Reactor Compatibility:

[0180] Energy generation wells are designed to be compatible with any type of containerized SMR, with the requirement that it can be configured to be conveyed underground within a cylindrical wellbore of the large-bore diameter range, and can be operated remotely from surface. Reactor types include, but are not limited to, gas-cooled reactors, high-temperature gas-cooled reactors (HTGR), pressurised-water reactors (PWR), boiling water reactors (BWR), molten salt reactors, heat-pipe reactors, travelling wave reactors, light-water reactors (LWR), heavy -water reactors (HWR), pebble-bed reactors, breeder reactors, and fusion or hybrid fusion-fission type reactors. In a further embodiment, the reactor is a self-contained thermal-electric generator, and the energy generation wellbore directly produces electricity using an umbilical power cable between the reactor module and surface, without requiring a downhole heat exchanger module 138 or dual -tubing secondary coolant loop 140.

[0181] The energy generation wellbore is compatible with reactor designs which can be operated, controlled, and shut down remotely, and feature fail-safe, intrinsic, or passive safety features. In addition to the safety of the reactor design, well containment barrier management and radionuclide containment boundaries within the wellbore function to prevent any harmful release of radionuclides to the environment in the event of equipment malfunction, accident, or operational error. Design of reactor components and nuclear technology is not an aspect of this invention.

[0182] Standardised TGU Modules: Factory building a standard TGU module and heat exchanger module off-site, in highway transportable units, improves construction timelines and further reduces costs by ensuring most components are constructed off site. In many embodiments, the energy generation wellbore’s geometry uses reactor components that are cylindrical and designed for downhole conveyance, leading to a modular and streamlined approach to construction.

[0183] Heat Exchanger Design:

[0184] The nuclear island includes a downhole-designed heat exchanger to efficiently transfer thermal energy from the reactor to the working fluid used for power generation. The heat exchanger module 138 functions to separate and control heat transfer between the primary coolant and the secondary coolant.

[0185] According to one aspect of some embodiments, the heat exchanger module 138 is a helical coil once-through steam generator with a helium circulator. This compact heat exchanger design can be sized to fit within a 4 ft - 20 ft diameter wellbore and operate within the desired power output range. The flow loop of coolant within the heat exchanger is shown in Fig. 8 in which the primary coolant loop 136 exchanges heat at the heat exchanger 138 with the secondary coolant loop 140. In the embodiment shown, the heat exchanger employs internal helical coils 354 to exchange heat between the primary coolant loop and the secondary coolant loop. At least one of the outlet tube and inlet tube is fitted with a thermal expansion joint between the pipe and the heat exchanger 138 to account for differences in thermal expansion between the outlet tube and the inlet tube. In various embodiments, and as illustrated in Fig. 8, the thermal expansion joint 156 is fitted between the inlet tube 128 and the heat exchanger 138 and it may comprise a seal-stack 156A and polished bore receptacle 156B. In various embodiments, the heat exchanger module can be configured in various arrangements and structures.

[0186] According to some embodiments, the thermal power is converted into useful process heat within a single or multiple downhole heat exchanger modules within the nuclear island.

[0187] According to some embodiments, the heat exchanger module 138 is included as part of the reactor module(s) 106 and is not a separate component.

[0188] Downhole coolant pump:

[0189] A downhole coolant pump may be incorporated as a standalone module or as an integral component of the TGU module(s) or heat exchanger, depending on the TGU module type and primary coolant used. The purpose of the downhole pump is to circulate primary coolant through the TGU module and heat exchange module. The downhole pump will be configured for liquid, gas, or multiphase fluids as required by the SMR type. In one embodiment where a separate pump unit is connected between the TGU module and heatexchanger, the pump type may be adapted from the conventional electric submersible pump (ESP) design similar to those used for artificial lift techniques in oil and gas.

[0190] Containment Cap Installation:

[0191] Once the reactor is installed near the bottom of the wellbore, a wellhead containment cap 162 and tubing hanger system is installed (Fig. 17, Fig. 18) to land-off the installation at the wellhead. Sealed ports in the tubing hanger and tubing hanger spools in the Xmas tree (“tree”) provide barriers allowing the safe operation of subsurface monitoring and control equipment. A tree is installed above the tubing spool which includes a manifold of valves which facilitate the coolant (i.e. water and steam) flow between the wellbore and facilities piping. Additional safety measures may include the placement of the entire wellhead and tree slightly below ground level in a cellar or caisson 166. The wellhead and tree enclose and seal the wellbore off at surface and connect it to the facility process piping. Connections and seals which are relied on as containment barriers in the wellhead, tree, and associated piping are tested prior to commissioning. The wellhead and tree, in combination with the deep operating depth of the reactor, separates the nuclear island from aircraft impact or other ground level disturbances.

[0192] Fig. 20 illustrates the top view of an embodiment of a containment cap in which there is an inlet port 124, an outlet port 126, and multiple sealed ports 134, including a first sealed port with a conduit tube into the wellbore 134A for instrumentation and monitoring 458 and additional sealed ports 134B which may provide conduit tubes for instrumentation cables which monitor and control downhole equipment or redundant coolant systems. The various sealed ports may be independent and separate ports.

[0193] Operations:

[0194] The reactor and heat exchanger are monitored within the wellbore remotely and can be inspected remotely using cameras, sensors, and robotic systems, or are retrieved from the wellbore for inspection, maintenance, refuelling or decommissioning by removing the containment cap and tubing from the well at surface, which the heat exchanger and reactor(s) are integrally connected to.

[0195] Refuelling and Maintenance:

[0196] The energy generation well is designed to allow for safe and efficient refuelling of the reactor module(s). Depending on the specific reactor design, refuelling intervals can range from 6 months to 50 years. Once the wellbore is de-energized, plugs may be installed in the tubing, and the containment cap 162 is removed and equipment retrieved in the reverse process to which it was installed.

[0197] In one aspect of some embodiments, once a reactor unit reaches the end of operating life, refuelling may occur by a shut down of equipment followed by the retrieval of the coolant piping, heat exchanger, and TGU, in reverse operational order to how it was installed. New TGU module(s) may then be installed in the same manner as the original TGU module(s), by conveying the downhole equipment and tubing back into the hole.

[0198] In another aspect of some embodiments, a depleted TGU module is suspended in operation and allowed to cool within the wellbore. A new TGU may then be installed above, and the cooled depleted TGU module removed for off-site disposal of spent fuel and refuelling.

[0199] In another aspect of some embodiments, a depleted TGU module is disposed of within the energy generation wellbore and is isolated downhole in an impermeable bedrock. A new TGU may thenbe installed above.

[0200] In another aspect of some embodiments, the TGU is configured with a liquid- fuelled SMR design, wherein new fuel may be pumped into the reactor though an additional service tubing string. In one aspect of this configuration, a helium-activated, nitrogen precharged gas-lift mandrel system utilised in combination with a liquid uranium salt fuelled reactor to defuel and refuel a single or multiple TGU reactor modules in a controlled sequence, or to selectively abandon a malfunctioned reactor and reposition the fuel into an active one.

[0201] In yet another possible configuration with a pebble bed SMR design, additional fuel pebbles may be dropped or pumped into the reactor module for refuelling through an additional service tubing string. In one aspect of this configuration, a remote operated frac ball launcher system can be utilized for refuelling a pebble bed reactor configuration within the nuclear island above the reactor. Like shale-oil completion systems,a ball-launcher refuelling system will hold multiple fuel pellets, come preloaded with fuel, and will utilise hydraulic control lines from the surface.

[0202] In another aspect of some embodiments, the deep inner casing string allows the commercialization and operation of reactor types that operate in a manner that continuously refuel by moving the critical region of the reactor core vertically up in the wellbore over time, such as a travelling wave reactor, or otherwise.

[0203] The wellbore may also be filled with nitrogen or another inert fluid for maintenance.

[0204] Cooling and Storage of Spent Fuel: In a further embodiment, the energy generation wellbore can be used for long-term cooling and / or storage of reactor modules with spent nuclear fuel, depending on local geology and well depth. The wellbore's large volume acts as a coolant pool capable of storing significant amounts of coolant around the reactor. Operating a reactor deep underground in impermeable bedrock also offers a longterm solution for spent-fuel storage.

[0205] Decommissioning and Abandonment: energy generation wells are designed with decommissioning considerations in mind. The TGU module when configured with a SMR can be retrieved from the wellbore for dismantling and disposal at a licensed facility. The wellbore itself can be permanently sealed with cement plugs, ensuring long-term containment and environmental safety.

[0206] In one aspect of some embodiments, the TGU module(s) remain in-situ within an impermeable bedrock.

[0207] In the initial embodiment, internal equipment including outlet tube 130, inlet tube 128, heat exchanger 138, and TGU module(s) 106 will be removed from the wellbore at the end of useful life. Any radioactive components will be permanently isolated downhole or disposed of in accordance with Nuclear Industry standards. The wellbore will be abandoned using industry techniques for the abandonment of wellbores, open shafts and caverns, which primarily consists of pumping cement within the wellbore to create a permanent isolation. Permanent isolation plugs will be installed to isolate potential irradiated casing surrounding the reactor module from the environment.

[0208] While the initial embodiment will remove the reactor and spent fuel from the wellbore at the end of the operating life, contingency boundaries are also devised in case of emergency or if the reactor becomes irretrievable, as shown in Fig. 14. A first boundary 408 is defined by reactor fuel container 406 containing fuel and radionuclides 404. The reactor vessel 410 and the reactor internal heat exchanger 402, if present, define a second boundary 412. The third boundary 414 is defined by the well casing 112 as well as the external heat exchanger 138. The third boundary may include additional boundary elements such as a multi-string packer 132 which seals around the secondary coolant loop or an inert fluid 322 around the reactor vessel which is designed to provide radiation shielding. A fourth boundary is defined by the surrounding formation rock, annular cement, and wellhead containment cap. Anemergency boundary 416 is defined by internal cement plug, or alternative internal and annular sealing elements such as resin or thermite 318 bonded between the casing 112 and borehole wall 120 to isolate the nuclear island underground.

[0209] Safety and Reliability Features

[0210] The energy generation well incorporates multiple safety features to enhance safe operation and provide additional risk mitigations:

[0211] Overheating Mitigation:

[0212] The rock formations 320 surrounding the borehole act as a passive heat sink, aiding in heat dissipation during normal operation and in case of emergencies. Additionally, the wellbore can contain a large volume of fluid which can be filled from surface, as shown in Fig. 1 A, to provide additional thermal mass. Additionally, SMR designs may incorporate inherent or active safety features to prevent overheating. Calculations performed using the method shown in Fig. 13 indicate that in some embodiments, a 10 ft diameter and 1500 ft well depth for some reactor configurations would be sufficient to provide in excess of 130% of required coolant pool capacity.

[0213] In another aspect of some embodiments, liquid filling the well will create significant heat dissipation via natural convection within the well and conduction into the casing, cement, and surrounding rock, to further mitigate the consequences of a reactor overheating. The ultimate heat sink in an emergency shutdown scenario is the rock surrounding the borehole, which provides a large thermal mass to dissipate heat.

[0214] The wellbore may have a volume capacity that allows a sufficient liquid volume within the casing to provide reactor cooling in a shut-down or emergency scenario naturally and without a pump.

[0215] In an exemplary embodiment, this uses convection principles around the inlet tube and conductive heat transfer into shallow formations as a heat sink, which replaces the need for wet or dry cooling towers at surface to condense residually heated vapour from the steam turbine outlet.

[0216] The ability to utilize passive cooling mechanisms to cool a reactor after reactor shutdown contributes significant efficiency and margin of safety to the reactor. In the event of an emergency, the reactor will continue to produce about 7% of its prior operating power, with that value decaying over several weeks as the radioactive fission products producing the heat decay. Relying on active heat removal mechanisms (emergency water pumps) can drive up the expense of traditional nuclear reactors. By incorporating passive heat removal into the reactor and the structure that it resides in, potential costs are reduced and margin of safety is improved.

[0217] Containment Boundary Management:

[0218] In operating a nuclear reactor underground, containment of nuclear fuel and associated byproducts is paramount to the safe operation. Depth and location within a deep borehole may not be sufficient on its own to ensure complete containment of radionuclides beneath the surface and therefore additional containment measures are utilized in various embodiments. In the event of an accident, radionuclides are contained by various isolation and containment measures. Various levels are isolated in the well bore to ensure that radionuclides released in a hypothetical accident must traverse various barriers to reach the surface. Heat exchangers isolate various sections of coolant inside compartments defined by the barriers. Additionally, the mass of liquid within the wellbore and the mass of rock around the wellbore contribute to cooling in the event of an accident. In the conventional operation of wells, a barrier philosophy is used to separate wellbore fluids from the external environment. Wellbore boundaries describe the radionuclide containment design for testing and operating a reactor underground, as shown in Fig. 14. Additional boundaries may beincorporated into the reactor design (between boundaries 2 and 3) or with additional heat exchangers, plugs, fluids, or emergency fast-closure systems.

[0219] According to one aspect of some embodiments, the characteristics of certain rock formations surrounding the wellbore may provide a robust passive containment barrier, in combination with verified annular cement isolation.

[0220] According to one aspect of some embodiments, where the reactor design facilitates water submergence, the wellbore around the reactor is filled with water or a similar fluid that serves as radiation shielding, whereby the depth of water shielding is selected based on the specific details of each reactor, such as the temperature and radionuclides assumed in a fission product release scenario. Water acts to reduce gamma and neutron damage to components of the wellbore outside the reactor vessel. It also acts as a mechanism to reduce the transmission of any fission products released in the event of an accident, similar to a wetwell in a BWR.

[0221] According to another aspect of some embodiments, additional boundaries may be incorporated into the design using additional casing strings, or within the wellbore using additional heat exchangers, packers or plugs, inert fluids, emergency safety valves or fast-closure systems.

[0222] According to another aspect of some embodiments, a preinstalled thermite- activated bismuth alloy plug of which the thermite reaction is activated at a precise temperature in the unlikely event of a thermal runaway of a reactor, and automatically melts the bismuth to seal the wellbore, creating a rock-to-rock permanent isolation barrier plug above the reactor.

[0223] Isolation Plugs: In the event the reactor malfunctioned or was irretrievable from the wellbore, isolation plugs similar to those which have been utilised in the oil and gas industry for plug and abandonments can be set to isolate the reactor. When set across impermeable rocks, wellbore plugs such as cement, resins, asphaltites, thermite-melted rock, bismuth alloys, or a combination thereof, may be used to isolate the reactor underground permanently.

[0224] Ground-Level Protection: The wellhead at the top of the wellbore may be located in a cellar below ground level, and may be equipped with shielding and blastprotection measures to further mitigate the effects of any potential incidents. The deep underground installation of the reactor provides enhanced protection against various groundlevel hazards, including but not limited to: flooding, seismic events, severe weather conditions (e.g., hurricanes, tornadoes), surface collisions, and potential acts of sabotage.

[0225] In one aspect of some embodiments, subsurface tubing hang-off systems similar in function to a subsea mudline suspension system is utilised to provide a load shoulder within the wellbore to hang-off tubing holding the reactor system in tension. With the reactor already at a depth below ground level and below aircraft impact depth, this also prevents dropping the reactor to the bottom of the well in the event the wellhead is damaged or completely removed.

[0226] Radiation shielding to minimize dose to components: Fluids and materials around the reactor may improve radiation shielding which protects downhole components from gammas / neutrons released from fission within the reactor vessel.

[0227] Underground Nuclear Island: The underground nuclear island is a feature of containing nuclear components deep underground. In the event of a leak in the primary coolant system, or between primary and secondary coolant systems, underground leak detection and radiation monitoring systems will identify it, and isolation practices will be utilised to control the leak before any exposure limits would be reached within the wellbore containment system at surface. This specification break between nuclear and non-nuclear components at the wellbore may reduce the permitting and construction times of surface facilities, which is a challenge for SMR commercialization.

[0228] Fissile Fuel Proliferation: Access to the reactor and fuel inside a wellbore would be extremely difficult. Specialised equipment is required to access and retrieve the tubing, heat exchanger, and reactor vessel from the wellbore before fuel access is possible. Low-enriched uranium fuel use further reduces this risk.

[0229] Hazard Assessments and Emergency Response: A nuclear wellbore system is intended to tolerate worst-case accidental or malicious attack surface impacts by placing the reactor below surface accident scenario cratering depth.

[0230] During operation of the reactor, there are four anticipated potential problems. The first is overheating of the reactor. This can be detected with a temperature sensor. The solution for reactor overheating during operation is to shut the reactor down using whatever mechanism is designed for that reactor design. Potential solutions for reactor overheating after reactor shutdown include increasing coolant flow or passive heat removal using the surrounding rock. The passive heat removal may be aided by a fluid filling the wellbore. A second potential problem is motion in the well, such as seismic activity or surface disturbance. This can be detected by an accelerometer. The first solution is to shut the reactor down. A solution to allow reactor restart is to inspect and secure in place. This can be done with brackets and vibration dampers.

[0231] A third potential problem is release of radionuclides from the reactor vessel. The release of radionuclides can be detected with radiation sensors or continuous air monitors. These sensors would need to be isolated from the radiation field of the normally operating reactor via shielding or distance. The design of the energy generation well with multiple radionuclide barriers between the reactor and the environment is engineered to mitigate release of radionuclides. Detection of airborne radionuclides above set thresholds could result in escalating action including reactor shutdown, coolant isolation, insertion of additional grout or cement, and activation of a thermite isolation mechanism.

[0232] A fourth potential problem is power loss. In the event of power loss to the reactor controls, or power loss at the surface facility, the intrinsic safety features of reactor designs utilised in an energy generation well allows them to remain safe. In addition, the hydrostatic pressure of the column of water in the wellbore around the reactor allows natural circulation to reach the reactor, without requiring any powered units pumping into the well, allowing heat removal from the reactor. The combination of hydrostatic pressure aided flow with the large thermal mass of the wellbore coupled to the surrounding rock will prevent a reactor core meltdown.

[0233] Wellbores with redundant radionuclide barriers and other features described herein meet the requirements for a containment building as outlined by nuclear regulatory agencies worldwide. Multiple layers of isolation are utilized between the reactor fuel and theoutside environment where people could be exposed to the radioactive material released from the fuel. Multiple barriers provide defence in depth for a broad range of potential accident scenarios. When multiple barriers are effective, the resulting overall leakage rate is the time-weighted mathematical product of the leak rate of each barrier to take into account decay of radionuclides in each section between barriers.

[0234] Additional Embodiments

[0235] In some embodiments the TGU includes a high-temperature gas-cooled reactor (HTGR) sized to fit within a 10 ft diameter casing vessel. The wellbore houses a single reactor and single heat exchanger as shown in Figs. 3 and 3B.

[0236] Additional embodiments may utilise multiple TGU modules stacked vertically within the wellbore.

[0237] Additional embodiments of the TGU may utilise molten salt reactors, liquid metal cooled reactors, light water cooled reactors, or heavy water cooled reactors.

[0238] In the initial embodiment surface facilities utilise the high temperature coolant through piping connected to an underground heat exchanger unit, to convert to steam for electricity generation or for use directly as process heat.

[0239] In additional embodiments, the TGU within the energy generation wellbore is configured to operate any reactor type, whereby surface facilities can utilise the reactor’s primary or secondary coolant fluid through piping or heat pipes connected to an underground heat exchanger unit, for multiple applications such as electricity generation or directly as process heat.

[0240] In the initial embodiment, the reactor is powered by tri-structural isotropic particle fuel (TRISO), which provides containment boundaries as shown in Fig. 14.

[0241] In additional embodiments, the reactor may be powered by any type of nuclear fuel such as uranium in a liquid salt form, metal uranium, or ceramic forms of uranium as the primary fission product boundary. All potential fuel forms may also contain plutonium from reprocessing spent fuel and uranium of any enrichment may be used.

[0242] The initial embodiment depth of operation locates the reactor at 1500 ft true vertical depth (TVD) within the wellbore, or at least 100 ft below deepest potable groundwater (10), whichever is deeper. The hydrostatic pressure at this depth creates apressure of approximately 650 psi, which removes the requirements for pumping coolant into the heat exchanger and can also provide pressure for other reactor cooling systems.

[0243] In additional embodiments, the depth of operation is between 100 - 10,000 ft TVD. In various embodiments, the depth of operation may be between 500 - 1000 ft TVD, between 1000 - 1500 ft TVD, between 1500- 3000 ft TVD, between 3000- 6000 ft TVD, and between 6000 - 10,000 ft TVD. In various embodiments, the depth of operation may be selected based on a combination of providing sufficient volume of coolant based on depth and sufficient hydrostatic pressure to provide circulation without additional pumping pressure.

[0244] The initial embodiment of the secondary coolant loop 140 includes two strings in the initial embodiment, one inlet tube 128 which is a low temperature pipe for liquid coolant down, and an outlet tube 130 for the coolant once converted to high temperature gas and is connected to the heat exchanger module as shown in Fig. 8.

[0245] In additional embodiments an inert fluid within the wellbore casing vessel and surrounding the inner tubing / piping and vessels also acts to control and manage heat transfer.

[0246] In an embodiment with a HTGR, the heat exchanger module contains a pump for the primary coolant. This is beneficial to address the minimal hydrostatic density change in helium gas when heated which can make natural circulation impractical.

[0247] In additional embodiments, the heat exchanger module may contain a pump for the primary coolant or use natural convection.

[0248] In an embodiment, the hot outlet tube 130 is dual-walled with an air-gap to prevent heat loss and calculations have shown that at a downhole heat exchanger outlet temperature of approximately 577 deg. C, wherein there will be approximately 20 deg. C temperature drop, resulting in an outlet temperature of 557 deg. C at surface.

[0249] In additional embodiments, the hot outlet tube 130 is dual-walled or singlewalled, and multiple pipes may be used in combination with additional Xmas trees, multibore tubing hangers, or a combination thereof.

[0250] In an additional embodiment, a drainage vessel is included below the lowermost reactor vessel to support the draining and recirculation of liquid fuel from certain reactor types.

[0251] In some embodiments, electrical power generation equipment 144, 172 is positioned within the wellbore below the wellhead and tree. For example, as illustrated in Fig. 19, the power generator 144 is a steam turbine unit positioned beneath the ground / sea bed level and beneath the wellhead and tree. In some such embodiments, the piping of the secondary coolant loop 140 connecting the power generator 144 with the heat exchanger module 138 comprises a down pipe 148 and an up pipe 146 circulating relatively cooler fluids down the down pipe 148 and heated fluids up the up pipe 146. While the piping of the secondary coolant loop is described here as a down pipe 148 and an up pipe 146, various features of the secondary coolant loop 140 as described in other embodiments comprising an inlet tube 128 and an outlet tube 130 may be applicable to the down pipe 148 and up pipe 146, including, but not limited to, such features as a polished-bore receptacle and seal-stack and / or insulation features such as an annular gap. In the claims, the term “inlet tube” includes a down pipe 146 connecting to power generation equipment within the wellbore, and the term “outlet tube” includes an up pipe 148 connecting to power generation equipment within the wellbore.

[0252] In such embodiments, electricity is generated entirely within the wellbore and may then be transmitted into the grid directly from connections fitted to the wellhead, for example via transformer station 472. Configuring electrical power generation equipment within the wellbore further increases the resilience of the power generation installation and can increase the tolerance of the installation as a whole to various hazards, including accidental or malicious incidents. Optionally, the power generator may be cooled by an external fluid coolant source 470.

[0253] Additional embodiments may utilize the following adaptations of existing oilfield and geothermal wellbore technologies and equipment:

[0254] Thermal Expansion Design: The utilisation of high-temperature well design methodology for oilfield and geothermal wells, which account for the thermal expansion lengths of tubulars is incorporated in the design to allow a sump below the reactor and a vertical degree of freedom for internal components, such as the heat exchanger and reactor, to allow up and down movement as the piping expands and contracts when in thermal operation.

[0255] Production Equipment: The utilisation of dual or multi-string production packer around the inlet and outlet tube for containment boundaries. The utilisation of a polished-bore receptacle and seal-stack 17 on the tubing inlet tube near the heat exchanger to account for the difference in thermal expansion between the hot outlet tube and the cooled fluid inlet tube.

[0256] Subsurface flow controls: The utilization of wellbore plugs, packers, valves, manipulating sleeves, and other downhole devices, to control flow or place additional containment boundaries within the wellbores

[0257] Wellhead and Xmas Trees: The utilisation of a thermal wellhead and tree designs typically used for steam assisted gravity drainage (SAGD), steam flood, provide high temperature and high pressure seals in the design. The lower flange of the wellhead will contain a crossover which adapts between the Xmas tree tubing sizes, and wellhead size.

[0258] Tubing Hangers: The utilisation of hanger systems such that the heat exchanger and thermal generation units are supported at surface when connected to the tubing with provisions for thermal operation. Tubing is connected to the tubing hanger and is typically held in tension using lock-down components within the tubing spool. Downhole components are integrally connected to the tubing at surface and are retrievable using one or combination of oilfield rigs, workover equipment, coiled tubing, or lifting cranes.

[0259] Completion Fluids and Brines: The utilisation of coolant pool fluids with various densities and hydrostatic column heights, such that the external pressure around the reactor vessel and heat exchanger can be controlled, and the buoyancy of the system can be controlled to manage tubing stresses during installation. The coolant fluid may also be a gas for reactor designs which are not suited to a liquid outer environment.

[0260] Well Intervention Equipment: The utilisation of intervention equipment and wireline, slickline, or coiled tubing and tools to install plugs to provide barriers that allow for the temporary removal of the wellhead system to maintain critical equipment or perform inspections of the reactor when downhole.

[0261] Downhole Monitoring Equipment: The utilisation of downhole instrumentation gauges which are installed on cables, through sealed wellhead ports to remotely monitor and control the reactor from surface. The utilisation of downhole hydraulicand electrical control or power lines to remotely monitor, power, and control instrumentation and downhole reactor components. Fibreoptic cables may also be used for downhole monitoring.

[0262] Well Abandonment Equipment: The utilisation of abandonment equipment such as mechanical or inflatable plugs, cement, and advanced materials like thermite and bismuth to provide isolation plugs for decommissioning of the wellbore after the reactor is removed, or as contingency or emergency isolations.

[0263] Geothermal Well Equipment: High-temperature tubing of similar size and metallurgy to that used in high temperature geothermal wells may be used in the outlet tube 130 connecting the heat exchanger to the surface.Hydrogen Storage Well

[0264] Another configuration of the energy generation or storage wellbore, various embodiments present a hydrogen storage well which repurposes the large-bore wellbore as a high-volume, low-pressure hydrogen storage vessel. These vessels will have the same 4 ft to 20 ft diameter and a storage capacity in the range of 5 tonne to 250 tonnes of hydrogen gas. This section details the design and operation of this configuration. The completed hydrogen storage wellbore acts as a sealed, cylindrical vessel capable of storing large volumes of hydrogen gas at relatively low pressures (below 5000 psi) due to pipe body hoop stress limitations. In an embodiment, the hydrogen gas may be injected and stored at pressures below 1000 psi. The low pressure large-bore wellbore approach addresses the challenge of hydrogen's low volumetric energy density by providing a large volume container, enabling economical storage without the need for expensive high-pressure compression. In some embodiments, the hydrogen gas may be injected into the hydrogen storage directly at production pressure. In some embodiments, hydrogen is compressed and higher storage pressures may be used by ensuring annular cement coverage of the casing which transfers hoop stress from the casing internal pressure load to the surrounding borehole wall.

[0265] Wellbore Sizing

[0266] Wellbore diameter is selected depending on the quantity of hydrogen storage required. To reduce the cost of storage, it is beneficial to utilize the maximum drilling depthof the large-bore equipment employed while optimizing the diameter using the method developed below.

[0267] In an embodiment of some embodiments, the wellbore has a diameter that may be sized using optimization calculus to determine a borehole diameter and casing diameter which maximizes the energy storage capacity of the wellbore

[0268] According to one aspect of some embodiments, a method is provided for determining the optimal wellbore diameter to reduce the cost of storage. To determine the maximum hydrogen storage mass as a function of wellbore radius, three substitutions are made into the ideal gas law.

[0269] Firstly, Barlow’s formula is used to correlate pressure at internal yield, as a function of hole radius.

[0270]

[0271] Secondly, Volume (assumed equivalent to casing volume) is also represented as a function of hole volume.

[0272]

[0273] Thirdly, maximum drilling depth (h) for a specific type of large-bore drilling equipment is represented in Equation 3.1, as a function of radius (r). Independent constants A and B are a linear-fit relationship constants based on empirical drilling data for hole size versus maximum drilling depth.

[0276]

[0277] Radius can be expressed as a function of storage mass, as shown in Equation5.5, by substituting equations 5.1, 5.2, and 5.3 into the ideal gas law.

[0278] Where:

[0279] m = Mass of hydrogen (gram)

[0280] P = Pressure (pascals)

[0281] T = Temperature (Kelvin)

[0282] n = moles, equivalent to m / M.

[0283] M = molar mass (g / mol)

[0284] R_H2 = gas specific constant (Joules / (g*K))

[0285] f_ymin = Specified minimum yield strength (pascals)

[0286] t = vessel wall thickness (m)

[0287] h = maximum drilling depth (m), equivalent to casing height.

[0288] r = hole radius (m), equivalent to half the casing diameter.

[0289] A, B = Drilling equipment specific independent constants.

[0290] In an embodiment, the optimal diameter of the hydrogen storage wellbore may be calculated according to:and,based on a target mass of hydrogen for storage for the energy generation or storage site, where m is a mass of hydrogen in grams, P is pressure in pascals, T is temperature in Kelvin, n is the number of moles, equivalent to m / M, M is molar mass in g / mol, RH2 is a gas specific constant in Joules / (g*K), fymin is a specified minimum yield strength in pascals, t is vessel wall thickness in meters, h is maximum drilling depth in m and is equivalent to casing height, r is hole radius in m which is equivalent to half the casing diameter, and A and B are drilling equipment specific independent constants.

[0291] Wellbore Design

[0292] The construction process for the hydrogen storage wellbore is similar to that of the nuclear well, as shown in Fig. 2. However, there are certain adaptations specific to hydrogen storage are made:

[0293] Casing Material Selection: The casing material is carefully chosen to be resistant to hydrogen embrittlement, and cyclic fatigue, ensuring long-term integrity and safety of the storage vessel.

[0294] Leak Tightness: Stringent quality control measures and inert-gas pressure tests are implemented during construction to ensure the wellbore is completely leak-tight, preventing any hydrogen leakage into the surrounding formations.

[0295] Hydrogen Storage Integration

[0296] Capacity: The storage capacity of a hydrogen storage wellbore depends on its diameter, depth and operating pressure range. For example, an 8 ft diameter wellbore can store approximately 10 tons of hydrogen gas at 600 psi. Multiple wellbores can be constructed on a single pad to achieve a desired total storage capacity.

[0297] Hydrogen gas can be injected into or withdrawn from the hydrogen storage wellbore through a wellhead and surface piping system. A hydrogen storage inlet tube 440 delivers injected hydrogen towards the bottom of the wellbore, to near the bottom end cap 114. A hydrogen storage outlet tube 442 allows for withdrawal of stored hydrogen from nearthe top of the hydrogen storage wellbore. An packer 444 can be installed to provide additional isolation above the hydrogen storage zone. The hydrogen storage zone can be entirely beneath the surface accident cratering depth 420 and optionally beneath the maximum groundwater depth 422

[0298] Injection: Hydrogen produced on-site (e.g., through electrolysis powered by the energy generation system) or transported from off-site sources can be injected into the wellbore using production pressure or compressors. The system is most compatible with low-pressure hydrogen gas, in the operating range of 13 psi - 3000 psi, and can store hydrogen from offsite production or on-site directly from electrolysis without requiring additional compression. Typically, hydrogen production via electrolysis or steam methane reforming, as well as hydrogen fuel cells, operate at low pressures (below 3000 psi).

[0299] Withdrawal: Hydrogen can be withdrawn from the wellbore as needed to meet demand, utilizing pressure control and flow regulation systems. It can then be used directly in fuel cells, compressed to meet pipeline specifications for transportation off-site, or to requirements for vehicle fuelling or transportation.

[0300] There may be provided an operating pressure range which is suitable for large-bore hydrogen storage, which is below a 5000psi wellhead equipment rating.

[0301] There may be used an outer surface casing which is designed to contain the hydrogen flow at shallow depths in the event of a leak.

[0302] Safety and Reliability Features

[0303] The hydrogen storage system incorporates monitoring and control systems to ensure safe and efficient operation.

[0304] Safety: The underground location of the hydrogen storage vessel enhances safety by minimizing the risk of surface-level accidents.

[0305] Pressure Monitoring: Pressure sensor instrument continuously monitor the internal pressure of the wellbore to ensure it remains within safe operating limits.

[0306] Temperature Monitoring: Temperature sensors track the temperature of the stored hydrogen.

[0307] Remote Operation: The entire system can be operated and monitored remotely through process control systems, enhancing safety and operational efficiency.

[0308] Additional Embodiments

[0309] In the initial embodiment, an optimal casing vessel diameter of 8 ft at 2000 ft depth is selected, resulting in a storage mass of 10 tonnes of hydrogen gas at low-pressure (600 psi).

[0310] In additional embodiments, a diameter between 4 ft to 20 ft is used, with storage mass capacity determined by max drilling depth, wall thickness, material yield strength properties.

[0311] In the initial embodiment, hydrogen gas is stored at pressure driven directly from electrolysis without additional compression to improve efficiency.

[0312] In additional embodiments, hydrogen gas is compressed to increase storage mass.

[0313] In an additional embodiment, the hydrogen storage well does not utilize internal tubing or Christmas trees above the wellhead, and process piping and flow valves are connected directly to ports in the casing vessel casing head housing flange at surface.

[0314] Surface Facility Tie-Ins

[0315] The facilities design includes the wellbore containment systems for energy generation and storage, in addition to surface equipment.

[0316] The hydrogen storage system can be seamlessly integrated with the energy generation system on the same site, creating a self-sufficient “standalone” energy facility as shown in Fig. 1. Electricity generated by the energy generation wellbores can be used to produce hydrogen through electrolysis, which is then stored in the hydrogen storage wellbores. This stored hydrogen can be used to generate additional electricity during periods of high demand or when the TGU, e.g. the nuclear reactor, is offline for maintenance or refuelling. Steam or gas generated from the energy generation wells can also further improve the efficiency of hydrogen production.

[0317] The energy generation site, when combined with hydrogen storage on-site, does not require off-site power input for startup or operation

[0318] In the initial embodiment, a hydrogen electrolyser module may be located on the same site and integrated as shown in Fig. 1. This configuration of the site has the abilityto use the heat from the nuclear energy generation well process to improve the efficiency of hydrogen production.

[0319] In another embodiment as shown in Fig. IB, one or more additional energy storage wellbores are also featured at a nuclear wellbore site to further improve the efficiency of the energy generation and storage site.

[0320] Surface Piping:

[0321] Surface piping connects to the energy generation or storage wellbore at the tree and wellhead valves as shown in Fig. 1 A. This provides a flow path for the energy generation and storage wellbore fluids to the relevant surface facilities which may be temporary (i.e. to facilitate startup tests) or permanent.

[0322] New Facility Construction

[0323] An initial embodiment of the energy generation or storage site is shown in Fig. 1. Energy generation or storage wellbores and surface facilities are constructed on site using the method shown in Fig. 2.

[0324] Integration with Existing Facilities

[0325] In another embodiment, energy generation or storage wellbores are integrated with existing surface facilities, and one or a combination of surface facilities are not required. As shown in Fig. IB, optional off-site tie-ins with existing facilities or infrastructure may be included with the energy generation or storage site.

[0326] Site Operation Methods

[0327] The energy generation and storage facility may provide electricity using the following methods:

[0328] Steam or gas produced from the energy generation or storage nuclear wellbore flows through the wellhead, Xmas tree and through piping which may contain chokes, gauges, and valves to a power generation turbine.

[0329] Electricity is produced from an electric generator coupled with the turbine.

[0330] Electricity is provided from a hydrogen fuel cell, which may have hydrogen supplied by an on-site electrolyser, hydrogen pipeline, hydrogen wellbore, or a combination thereof.

[0331] The energy generation or storage facility may provide process heat using the following methods:

[0332] Steam or gas produced from the nuclear energy generation wellbore may also flow directly to an industrial process (i.e. refinery, SAGD, steam-methane reforming process).

[0333] Combustion of hydrogen used as a fuel.

[0334] Conversion of electricity produced on-site into process heat using electric resistance heating, induction heating, electric arc furnace, heat pumps, infrared heating, or a combination thereof.

[0335] The energy generation or storage facility may produce hydrogen on-site using the following methods:

[0336] Electrolysis, such as alkaline water electrolysis, proton-membrane water electrolysis (PMWE), or steam-electrolysis, produces hydrogen on-site using electricity produced directly from nuclear energy generation steam turbine power, renewable power connected to the energy generation or storage facility, or from any source of grid-connected power. Steam or gas from the nuclear energy generation facility may be used in the electrolysis process to further improve hydrogen production efficiency.

[0337] Steam methane reforming, using steam from the nuclear energy generation wellbore combined with natural gas (primarily methane) from an off-site or on-site source, steam and methane react to produce syngas (a mixture of hydrogen and carbon monoxide), which can be further processed into pure hydrogen and carbon dioxide for off-site carbon capture and underground storage.

[0338] Thermochemical water splitting, using high-temperature gas from the nuclear energy generation wellbore to drive a sulfur-iodine cycle, which would produce hydrogen gas directly from an energy generation wellbore.

[0339] Methane pyrolysis through thermal decomposition or other pyrolysis pathways such as thermos-catalytic, microwave, plasma, etc. may also make use of the heat and electricity produced at a nuclear generation site to drive hydrogen production and storage.

[0340] The energy generation or storage facility when sited with additional energy storage wells, can provide storage for any method of energy production. In the initial embodiment, it will store energy by converting renewable electricity to hydrogen during times of overproduction in the hydrogen energy storage wellbore configuration. When the stored energy is needed, the hydrogen can be used directly via combustion for heating or converted back to electricity using hydrogen fuel-cells.

[0341] Hydrogen produced from renewables, either on-site or offsite can flow into the hydrogen storage wellbore for storage.

[0342] Hydrogen flows from the hydrogen storage wellbore to the demand source.

[0343] In an embodiment, the energy storage well may provide blackstart capability to the nuclear well. The energy generation or storage facility may provide blackstart power capability for an electric grid using the following method:

[0344] Hydrogen storage wellbores act as blackstart units.

[0345] During a power outage either onsite or in an interconnected grid, the site would automatically shut down (ESD).

[0346] First power restoration protocols are identified.

[0347] Start blackstart units; hydrogen flows from hydrogen storage units to a fuelcell and produces on-site electricity.

[0348] Nuclear energy generation wellbores are re-activated and steam / gas production resumes.

[0349] Steam / gas production reaches steam / gas turbines and power generation ramp- up commences.

[0350] Additional nuclear energy generation wells and hydrogen storage well units are synchronized and connected to restore critical power to transmission and distribution lines while remaining loads are restored.

[0351] Scalability and Reliability Features

[0352] Co-location within Industrial Sites:

[0353] Energy generation and storage wellbores can be installed within existing industrial sites which can meet the footprint requirements of the drilling rig and ancillary drilling equipment, removing the need for new site construction. The final footprint of thenuclear energy generation wellbore including wellhead and Xmas tree is approximately equal to the outer diameter of the wellbore (4 ft to 20 ft). The footprint of the energy generation and storage facility depends on the application, with the initial embodiment being similar to that of a geothermal power station.

[0354] Co-location of Energy Generation and Storage Wells:

[0355] When nuclear energy generation facilities are co-located with underground energy storage wells, referred to as hydrogen storage wells and additional energy storage wells, there are additional cost savings in utilising the same drilling equipment and capital equipment such as casing, cement, wellheads and trees.

[0356] Additional Energy Storage Integration: The large-bore energy storage wellbore 108 can store significant quantities of energy and provides the potential to convert power to “X”, where “X” is a variable representing multiple potential uses for the energy storage wellbores. Using the same large-bore wellbore design, energy generation and storage wellbores can integrate with many types of energy storage within the wellbore containment structure which include but are not limited to: thermal-mass energy, chemical energy, and hydraulic energy. Gravity-mass and flywheel energy storage may also be incorporated into the overall facility using the same drilling equipment, however these examples do not require a wellbore design since there is no internal pressure.

[0357] Flexible Power Generation and Storage Capacity:

[0358] Any number of energy generation or storage wellbores may be installed at each site. The low surface footprint of each energy generation or storage wellbore may also allow future power generation or storage capacity to be installed at the same site in the future without significant changes or additions to the existing surface facility. This provides a high level of flexibility to configure power generation capacity throughout the lifetime of the site. Each nuclear energy generation wellbore can contain a single or multiple reactor units, with power output depending on the diameter of the reactor, fuel grade, reactor type, and number of reactor modules. Each hydrogen storage or additional energy storage wellbore can have a customized energy storage capacity which is dependent on the diameter, depth, and operating pressure of the wellbore.

[0359] Geothermal Wellbore Integration: Energy generation or storage sites with nuclear energy generation wellbores may be co-located with geothermal energy production sites for increased efficiency by utilizing the waste heat from the underground nuclear power generation.

[0360] Utilisation of Oilfield and Geothermal Power Facility Equipment: The steam or gas turbine and electric generator in the Thermal Generation Unit Module (Fig. IB) will utilise equipment and industry standards similar to that used in the production of oil and gas, and generation of geothermal power. By utilising existing equipment from oilfield and geothermal industries, nuclear energy generation wellbores can be created more rapidly than by developing custom tools and equipment for the nuclear industry. In the initial embodiment, some surface facility equipment from geothermal and thermal steam injection (i.e. SAGD) well sites will be used. Geothermal and nuclear power stations have similarities in their method of converting steam to electricity. Energy generation or storage surface facilities will be modelled from geothermal surface facilities which can be constructed more rapidly and cost effectively than traditional nuclear construction. This is feasible by separating the surface facilities from the nuclear energy generation wellbore, which contains the nuclear island deep underground.

[0361] Grid Blackstart capability:Blackstart means the capability to provide power to the grid after a total grid failure. Energy generation or storage sites can provide grid blackstart capability for critical infrastructure with certain reactor designs, on-site stored energy, hydrogen fuel cells, or a combination thereof.

[0362] Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.

[0363] In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite articles “a” and “an” before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.

Claims

CLAIMTHE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTYOR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An energy generation or storage site comprising plural wellbores co-located at a common site, the plural wellbores including plural energy generation wells each containing a thermal generation unit, plural energy storage wells each storing energy, or the plural wellbores including at least one energy generation well and at least one energy storage well.

2. The energy generation or storage site of claim 1 in which the plural wellbores include at least one energy generation well and at least one energy storage well, and the energy storage well storing energy produced by the energy generation well.

3. The energy generation or storage site of claim 2 in which the energy storage well comprises hydrogen storage, the hydrogen being produced using energy from the energy generation well.

4. The energy generation or storage site of claim 2 or claim 3 in which the energy storage well provides blackstart capability to the energy generation well.

5. The energy generation or storage site of any one of claims 1-4 in which the plural wellbores are each between 4 feet and 20 feet in diameter.

6. The energy generation or storage site of any one of claims 1-5 in which the plural wellbores are each between 100 and 10000 feet deep.

7. The energy generation or storage site of any one of claims 1-6 in which each wellbore contains a respective casing string having a pre-installed sealed bottom-end cap of the respective casing string, the thermal generation unit or energy storage occurring within the respective casing string.

8. The energy generation or storage site of claim 7 in which each wellbore further comprises a respective surface casing extending to a depth below a maximum groundwater level depth at the energy generation or storage site.

9. The energy generation or storage site of any one of claim 3 or claims 4-8 as depending from claim 3, wherein hydrogen gas is injected at pressures below 5000 psi.

10. The energy generation or storage site of claim 9 in which the hydrogen gas is injected into the hydrogen storage directly at production pressure.

11. The energy generation or storage site according to any one of claim 2 or claims 3-10 as depending from claim 2, wherein the plural wellbores co-located at a common site are located at an industrial site or infrastructure to provide energy generation and storage for the industrial site or infrastructure.

12. The energy generation or storage site according to claim 11 wherein a heated coolant from the at least one energy generation well is conveyed to the industrial site or infrastructure for use in an industrial process.

13. A method of construction of a wellbore for power storage or energy storage, the method comprising: drilling a borehole; providing a casing having a sealed bottom end; assembling and sealing individual joints of the casing and lowering the casing assembly including the sealed bottom end into the borehole; sealing a cap to a top end of the casing, the cap including an inlet port for flow into the wellbore and an outlet port for flow out of the wellbore.

14. The method of claim 13 in which the casing is filled in use of the wellbore with an energy storage medium.

15. The method of claim 14, where the wellbore has a diameter sized using optimization calculus to determine a borehole diameter and casing diameter which maximizes the energy storage capacity of the wellbore.

16. The method of claim 15, in which the wellbore diameters of the hydrogen storage is calculated according to:Birr) and,based on a target mass of hydrogen for storage for the energy generation or storage site, where m is a mass of hydrogen in grams, P is pressure in pascals, T is temperature in Kelvin, n is the number of moles, equivalent to m / M, M is molar mass in g / mol, RH2 is a gas specific constant in Joules / (g*K), fymin is a specified minimum yield strength in pascals, t is vessel wall thickness in meters, h is maximum drilling depth in m and is equivalent to casing height, r is hole radius in meters which is equivalent to half the casing diameter, and A and B are drilling equipment specific independent constants.

17. The method of claim 13 in which the wellbore contains in use of the wellbore a thermal generation unit for power generation.

18. The method of any one of claims 13-17 further comprising the step of installing a surface casing in an upper portion of the borehole before the step of lowering the casing having a sealed bottom, and the method further comprising the step of forming a sealing connection between the surface casing and the casing having a sealed bottom after the step of lowering the casing including the sealed bottom.

19. The method of any one of claims 13-18 in which the borehole is 4 feet to 20 feet in diameter.

20. The method of any one of claims 13-19 further comprising installing an inlet tube connecting to the inlet port and an outlet tube connecting to the outlet port, and installing a packer within the casing having the sealed bottom, the inlet tube and the outlet tube extending below the packer.

21. The method of claim 20 in which the packer is below an expected cratering depth in the event of a surface accident.

22. The method of claim 20 or claim 21 as dependent on any one of claims 2-4 in which the inlet tube extends to a greater depth than the outlet tube.

23. The method of any one of claims 13-22 in which the cap comprises one or more additional sealed ports for monitoring of the wellbore and controlling downhole equipment.

24. The method of claims 23 in which the one or more additional sealed ports comprises separate ports for conduit tubes for instrumentation cables to monitor and control downhole equipment.

25. An energy generation facility comprising: a first borehole having a casing; a thermal generation unit within the borehole; a first coolant loop within the borehole for extracting heat from the thermal generation unit; a heat exchanger within the borehole and connected to exchange heat between the first coolant loop and a second coolant loop to cause heating or boiling of a second coolant within the second coolant loop to create a heated gas or vapour; power generation equipment connected to receive the heated gas or vapour from the second coolant loop, extract energy from the heated gas or vapour, and return the gas or vapour tothe second coolant loop within the borehole at least partially in liquid form, the gas or vapour recondensing within the borehole under passive heat transfer between the casing of the borehole and surrounding material.

26. The energy generation facility of claim 25 in which the second coolant loop comprises an outlet tube for carrying the second coolant from the heat exchanger to the turbine and an inlet tube for carrying the second coolant from the turbine to the heat exchanger, the borehole containing an additional volume around the outlet tube and the inlet tube, the additional volume containing a fluid for conductive and convective heat transfer between the inlet tube and the casing of the borehole.

27. The energy generation facility of claim 25 or claim 26 in which the circulation rate of the second coolant within the second coolant loop is maintained by a hydrostatic U-tube effect between the outlet tube and inlet tube that occurs under normal operation without a pump.

28. The energy generation facility of any one of claims 25-27 in which the wellbore has a volume capacity that allows a sufficient liquid volume within the casing to provide reactor cooling in a shut-down or emergency scenario naturally and without a pump.

29. The energy generation facility of any one of claims 25-28 further comprising a surface-powered downhole pump for causing increased circulation within the first coolant loop.

30. The energy generation facility of any one of claims 25-29 further comprising a circumferential vibration damper element containing an elastomeric material which is located between the casing and the thermal generation unit, and which seismically isolates the thermal generation unit.

31. The energy generation facility of any one of claim 26 or claims 27-30 as depending from claim 25, in which the outlet tube is dual walled.

32. The energy generation facility of any one of claim 26 or claims 27-31 as depending from claim 25, in which the second coolant system comprises multiple inlet and outlet tubes.

33. The energy generation facility of any one of claim 26 or claims 27-32 as depending from claim 25, comprising a thermal expansion joint between the inlet tube and the heat exchanger to account for differences in thermal expansion between the outlet tube and the inlet tube.

34. The energy generation facility of claim 33 in which the thermal expansion joint comprises a seal-stack and polished bore receptacle connecting the inlet tube to the heat exchanger.

35. An energy generation facility comprising: a borehole having one or more casings; plural thermal generation units within the borehole; a first coolant loop within the borehole for extracting heat from the plural thermal generation units; and a heat exchanger within the borehole and connected to exchange heat between the first coolant loop and a second coolant loop, the second coolant loop conveying heat from the heat exchanger to power generation equipment located inside or outside the borehole.

36. The energy generation facility of claim 35 in which the first coolant loop connects each of the plural thermal generation units in series at least in one of an upwards direction of flow and a downwards direction of flow.

37. The energy generation facility of claim 36 in which the first coolant loop connects each of the plural thermal generation units in series in both the upwards direction of flow and the downwards direction of flow.

38. The energy generation facility of claim 37 in which the downwards direction of flow between each successive pair of thermal generation unit occurs within a respective annulus surrounding a respective pipe containing the corresponding upwards direction of flow.

39. The energy generation facility of claim 38 in which the plural thermal generation units, the heat exchanger, and tubes of the second coolant loop are vertically connected and weight-bearing with a vertical degree of freedom to move up or down, to form a chain and to carry a load comprising a buoyancy-corrected weight of the chain and where the tubes of the second coolant loop are anchored in a containment cap at a surface end of the borehole which transfers the load through the containment cap to the one or more casings.

40. The energy generation facility of claim 39 whereby maintenance and refueling occurs by retrieving the tubes of the second coolant loop, to which the plural thermal generation units and heat exchanger are connected.

41. The energy generation facility of claim 40 in which each of the plural thermal generation units are removably connected to the chain for separate removal and replacement during maintenance or refueling.

Images