This includes light water nuclear reactors, particularly pressurized water reactors or boiling water reactors, that integrate autonomous passive decay heat removal systems.

Abstract

This invention relates to light water nuclear reactors, particularly pressurized water reactors (PWRs) or boiling water reactors, including an integrated autonomous passive decay heat removal system. The invention discloses a light water nuclear reactor (LWR), particularly a PWR or BWR, comprising: - a reactor core; - a system for removing at least some decay heat from the reactor core, comprising: a first water reservoir or pool disposed above the reactor core; a heat exchange device immersed in the pool; an organic Rankine cycle; a fluid loop; a second water reservoir different from the pool; and a second pump. The invention lies in installing an organic Rankine cycle and a supplementary water reservoir different from the pool, wherein the energy stored in the pool is the heat source for the organic Rankine cycle evaporator, and the supplementary water reservoir directly supplies the organic Rankine cycle condenser via a dedicated pump to constitute the cold source for the organic Rankine cycle condenser.

Description

Technical Field

[0001] This invention relates to the field of nuclear reactors, particularly pressurized water nuclear reactors and boiling water nuclear reactors.

[0002] More specifically, this invention relates to improving the decay heat removal capabilities of these nuclear reactors in accident scenarios. The aim is to integrate an autonomous passive decay heat removal system into the architecture of an advanced light water reactor (LWR) safety system.

[0003] Therefore, the object of the present invention is to mitigate the main drawback of prior art safety passive condensers or passive wall condensers, which is the requirement for very high water volumes, which burdens and complicates the civil engineering of nuclear facilities, is a serious limitation, especially in terms of earthquake issues, and increases costs.

[0004] A second advantage of the invention is that, due to the use of passive cooling via natural convection and a more compact exchanger due to improved heat exchange performance, better overall performance is achieved for this type of system, resulting in a smaller overall system volume.

[0005] It is important to remember that the decay heat of a nuclear reactor is the heat generated in the reactor core after the nuclear chain reaction stops, and it consists of the decay energy of the fission products.

[0006] Although described with reference to pressurized water reactors, the present invention is applicable to boiling water nuclear reactors or any light water nuclear reactor (LWR) that requires a large amount of water at a high altitude as a cold source, as currently envisioned as a safe decay heat removal device. Background Technology

[0007] A pressurized water reactor (PWR) consists of three cycles (fluid loops), and its general operating principle is as follows.

[0008] The pressurized water in the primary loop absorbs the energy supplied in the form of heat generated by the core fission of uranium and plutonium (if applicable) reactors.

[0009] This pressurized water at high temperature (typically 155 bar and 300°C) then enters a steam generator, transferring its energy to a secondary loop that also uses pressurized water as a heat exchange fluid. This water, in the form of steam at high pressure (typically around 70 bar), then expands through an expansion member, converting the fluid's enthalpy change into mechanical work, which is then converted into electrical work in the presence of a generator.

[0010] Then, the water in the second loop is condensed by the condenser, which uses the third loop (cooling loop) as the cold source.

[0011] Unlike pressurized water reactors (PWRs), boiling water reactors (BWRs) do not have a steam generator: they consist of only one loop for water and steam generated after evaporation within the containment. The water in the primary loop partially evaporates in the core. This water circulates under pressure, but at a lower pressure than that of a pressurized water reactor (typically 70 to 80 bar).

[0012] Publication [1] Figure 2 The general configuration of a boiling water reactor is illustrated. Water drawn from the condenser is pumped under pressure within the reactor containment via main pumps and enters the periphery of the reactor core within the containment. It is then mixed with and heated by a high-flow-rate saturated water produced by a steam-water emulsion separation process within the core. Upon exiting the core, the water-steam mixture is separated by gravity and centrifugation. The generated steam is directed to a downstream steam collector and turbine, while the saturated water is recirculated to mix with cooler water. The water mixture descends along the containment wall, where it is drawn into the core via a primary loop pump outside the containment and guided through the core, where the heat generated is extracted, resulting in heating to the saturation and evaporation points.

[0013] Boiling water reactors include safety condensers, also known as isolation condensers: these constitute the ultimate reliance for emergency cooling of the reactor core. [1] Figure 4 A schematic diagram of the isolation condenser arrangement is provided.

[0014] However, although the operation of light water reactors (LWRs) is known, mastered, and reliable, the history of nuclear energy, particularly the 2011 Fukushima Daiichi nuclear power plant accident, has demonstrated weaknesses in power plant management under extreme accident conditions, with prolonged grid outages exacerbated by the loss of internal power generation units and cooling sources.

[0015] Such accidents are particularly caused by defects in the removal of decay heat from the reactor. These accident sequences also occurred in the fuel cooling pool during the 2011 Fukushima Daiichi nuclear disaster.

[0016] The decay heat phenomenon in the reactor core is as follows.

[0017] When the nuclear reaction stops, the fission products that are decomposing continue to generate heat until a steady state is reached.

[0018] One second after shutting down the reactor, the heat generated accounts for 7% of the reactor’s rated thermal power.

[0019] Then, as in the published [2] Figure 1 As shown, it decreases over time.

[0020] For example, 72 hours after the reactor is shut down, it still accounts for 0.5% of the nominal thermal power. Therefore, it is crucial to remove this heat to prevent any risk of fuel deterioration or even meltdown in the reactor core.

[0021] For example, the VVER TOI pressurized water reactor has a nominal electrical power of 1300 Mwe and a nominal thermal power of approximately 3200 MWth. After being shut down for 72 hours, the reactor still produces approximately 20 MWth of residual thermal power.

[0022] Generally, efforts are made to improve the passivity and diversification of the system in order to dissipate decay heat and ensure better overall reliability. The goal is to maintain the integrity of the structure, namely the first containment barrier (fuel assembly liner), the second containment barrier (primary loop), and the third barrier (containment), even in the event of prolonged and widespread power shortages (corresponding to the Fukushima nuclear power plant scenario).

[0023] More specifically, since the Fukushima Daiichi nuclear power plant accident, much research has focused on passive decay heat removal technology within a few dozen hours.

[0024] The requirements for the new solution depend first and foremost on improved performance and reliability, as well as maximum possible operational autonomy before any human intervention and use of external hardware (i.e., at least 72 hours).

[0025] More importantly, in the context of this invention, an accident situation, other than battery power, is considered to be a prolonged (typically several days) power outage from any source. This situation is referred to as a plant-wide power outage (SBO).

[0026] In the event of an accident, without the need for active electrical systems, one effective means of extracting decay heat from the core of a pressurized water reactor is to cool the reactor core using a passive system. This involves cooling the core by diverting its heat energy to the atmosphere via air exchangers or to high-level water tanks (pools) for natural convection. This system is known as a Passive Residual Heat Removal (PRHR) system.

[0027] Passive waste heat removal systems have the same overall structure, regardless of whether cooling is achieved through air or water: the cooling loop is located at the outlet of the steam generator in the pressurized water reactor. Therefore, steam is fed into a parallel loop, where it is cooled and condensed by an air condenser or a water condenser, rather than being directed from the secondary loop to the turbine.

[0028] The first natural circulation loop transfers heat from the reactor core to the steam generator, followed by a second loop that transfers it from the steam generator to the condenser. Thus, residual heat from the reactor core is removed via the steam generator and the two natural circulation loops (which are therefore passive).

[0029] An example of an air condenser used for passive waste heat removal is an example of a VVER TOI pressurized water reactor, whose thermal and electrical properties have been mentioned above: the air condenser takes the form of a single-tube exchanger with circular fins of a serpentine integral structure.

[0030] The advantage of air condensers like this lies in the fact that air is an inexhaustible source of cold (in an open medium) and is naturally occurring. Therefore, this air condenser technology is completely independent of cooling time and there is no gradual loss of cold source.

[0031] The main drawback of this technology is the size of the air exchanger. In fact, due to the low heat exchange coefficient with air, the required volume and area of ​​the air exchanger are very large, and the heat extraction performance is highly dependent on weather conditions.

[0032] For example, the VVER TOI passive residual heat removal system is designed to extract residual heat equal to 2% of the reactor's nominal thermal power, or 64 MWth. To achieve this power, 16 exchange units with an area equivalent to several thousand square meters must be installed on top of the nuclear facility.

[0033] As mentioned above, the decay heat required to cool the pressurized water reactor core can be generated by a water condenser, such as... Figure 2 As illustrated schematically, reactor core 1 is connected to steam generator 2, and decay heat removal is provided by a passive natural circulation closed loop 3, which includes a steam generator leading to a water condenser 4, which is submerged in a water tank or pool 5 placed at an elevated location. Thus, loop 3 enables the transfer of heat energy from the steam generator to the water tank 5. During decay heat removal, the temperature of the water tank 5 rises to the boiling point of water. The water evaporates into the air with a certain kinetic energy under atmospheric pressure.

[0034] Many current projects use water as a cold source for passive waste heat removal, among which:

[0035] - Westinghouse's AP-600 and AP-1000 projects;

[0036] - The Hualong One project of China National Nuclear Corporation (CGNPC) and China National Nuclear Corporation (CNNC);

[0037] - The VVER1200 project of the Russian company ROSATOM uses a passive safety condenser that uses water as the cold source.

[0038] This decay heat removal system has the following main drawbacks.

[0039] First, the presence of water sources at high altitudes complicates and burdens civil engineering, as the safe cold source is required to maintain the integrity of the structure in the event of extreme impacts such as earthquakes or aircraft collisions.

[0040] Furthermore, due to the effect of water evaporation, the cooling time of the steam generator is directly related to the volume of the water tank: the larger the volume of water, the longer the cooling time. For example, the HPR1000 reactor with a nominal thermal power of 3060MW includes a passive residual heat removal system, which is designed to provide 72 hours of cooling, meaning a water tank volume of 2300m³ is required. 3 :[3].

[0041] Therefore, the problem with this system lies in the necessary trade-off between the civil engineering constraints of the pool and the achieved cooling time (typically a minimum of 72 hours).

[0042] The same problem arose with the removal of decay heat from boiling water reactors (BWRs), which in particular caused the core meltdown in several sections of the Fukushima Daiichi nuclear power plant. In this situation, the steam no longer originates from the secondary loop of the steam generators but comes directly from the reactor containment vessel. This steam must then be cooled and condensed to remove the decay heat from the core. The cold source required for the condensation and cooling of the primary steam must also be located at a height relative to the reactor core and be large in volume. The size of this cold source in the boiling water reactors involved in the Fukushima disaster was insufficient to achieve the currently most needed 72-hour passive operation.

[0043] Under existing accident protocols, containment cooling and depressurization systems for pressurized water reactors or boiling water reactors can also be used as decay heat removal devices, particularly in cases where the primary coolant loop is intentionally opened (the so-called "pressurization open" configuration in the final scenario) or unintentionally opened (in the case of a single coolant loss following a rupture-type accident). The final cooling source is specifically designed to remove decay heat associated with this cooling method.

[0044] In both of the above scenarios, these two types of passive safety condensers can only operate for extended periods if a sufficient amount of cold water is available to collect the necessary heat to cool the reactor core.

[0045] Similar to applications related to pressurized water reactors, the cold source must be located at a height relative to the reactor containment and the components formed by the containment shell to establish natural circulation, thereby enabling the removal of heat from the reactor core or the center of the containment shell.

[0046] Generally, natural circulation of a single-phase or two-phase fluid is possible if the cold source that increases the density of the fluid is located at a higher altitude than the heat source that decreases the density of the same fluid. Conversely, thermal stratification and blockage occur in the natural loop.

[0047] Therefore, due to the limitations imposed by the volume of water at higher elevations, autonomous cooling supply equipment will greatly expand the operational autonomy of this type of safety system compared to operation lasting only a few hours.

[0048] By way of example, the disclosed item [4] Figure 2 The following idea is given: the necessary volume of the cold source at a height specifically designed for the operation of a passive containment cooling system (PCCS), which serves as an isolation condenser for both final discharge and safe discharge.

[0049] In addition to the cooling system of the pressurized water reactor (PWR), the use of an organic Rankine cycle (ORC) machine in the event of an accident has been envisioned.

[0050] As mentioned above, the problem with using water for passive waste heat removal lies in the relationship between the volume of the pool and the cooling time.

[0051] Furthermore, one solution to this problem is to remove some of the energy accumulated in the pool using an exchanger. This exchanger then functions as the evaporator in the organic Rankine cycle. The condenser in the organic Rankine cycle is an aero condenser.

[0052] This solution enables the use of power generated by the organic Rankine cycle turbine to power a pump connected to an organic Rankine cycle via a turbine generator, resulting in an autonomous system capable of discharging some of the heat stored in the pool.

[0053] Therefore, this organic Rankine cycle can recover some of the energy stored in the pool as heat and discharge / remove it in a dedicated loop, thereby limiting the amount of water evaporating from the pool and thus extending the cooling time through the pool.

[0054] Therefore, patent application WO2012 / 145406 proposes this solution, but it is applicable to different fields. In fact, the heat energy fed into the pool comes from spent nuclear fuel that is still generating heat. Therefore, this technology applied to pressurized water reactors can alleviate some of the problems mentioned above. In fact, some of the heat energy stored in the pool can be removed through an organic Rankine cycle, which allows for an increase in the core decay heat removal time for a given pool volume.

[0055] However, while it can improve the ratio between cooling time and pool volume, the efficiency of this technology depends on the volume of the exchanger capable of dissipating heat to the final cold source (air). In fact, for the system to truly function throughout the cooling of a light water reactor, the power extracted by the exchanger in the pool cooling cycle must be on the same order of magnitude as the power exchanged between the pool and the reactor.

[0056] Currently, as mentioned above, in the case of a VVER TOI reactor, the decay heat of the reactor is approximately tens of MW.

[0057] Therefore, using the organic Rankine cycle proposed in the above applications to remove all or at least a large portion of the power exchanged between the pool and the reactor would require a huge facility volume, especially for the final air exchanger.

[0058] In other words, although it is able to extract decay heat from the reactor core over a longer given time compared to the organic Rankine cycle, the system proposed in patent application WO2012 / 145406 still has very limited practical use and is indeed effective for a few hundred kW of surplus power.

[0059] Patent application WO2013 / 019589 proposes a similar solution, namely, cooling the spent nuclear fuel by immersing it in a water reservoir and using the heat energy from the reservoir to run an organic Rankine or Stirling cycle. This patent application also proposes adding a thermoelectric module to utilize the heat generated by the spent fuel by converting it into electricity.

[0060] The novelty of these solutions according to WO2013 / 019589 lies in the use of electricity generated by these different systems in addition to the heat energy extracted from the pool, and the use of two water pumps, one of which draws water from the reservoir (pool) at the height of a high-mounted ventilator to cool it, and the other pump draws water from another reservoir to reduce water evaporation in the pool.

[0061] Therefore, thanks to these pumps, there is no longer a direct correlation between cooling time and pool volume, as the dedicated pumps can continuously supply water to the pool.

[0062] However, the solution based on WO2013 / 019589 has many drawbacks.

[0063] First, the heat exchanger for the cold source in a Stirling cycle or organic Rankine cycle is an air exchanger, and as mentioned above, these exchangers can be very large and must be located at a high position.

[0064] Furthermore, air exchangers are highly dependent on external temperature, and therefore also on their variability. Thus, to ensure their reliability, the system must be able to adapt to temperature variations within the geographical area of ​​the power plant.

[0065] Therefore, there is a need to improve the decay heat removal systems of light water nuclear reactors (LWRs), especially pressurized water reactors (PWRs) or boiling water reactors (BWRs), in order to mitigate the aforementioned drawbacks using organic Rankine cycles. Summary of the Invention

[0066] Therefore, in one aspect, the present invention relates to a light water nuclear reactor (LWR), particularly a pressurized water reactor (PWR) or a boiling water reactor (BWR), comprising:

[0067] - Reactor core;

[0068] - A system for removing at least some decay heat from the reactor core, the system comprising:

[0069] A first water storage tank or pool is arranged above the reactor core; a heat exchange device is immersed in the pool, such that the water in the pool cools the steam entering the device from the primary or secondary loop of the reactor.

[0070] Organic Rankine circulation system, including:

[0071] -Expander;

[0072] - Condenser;

[0073] -First pump;

[0074] - An evaporator arranged in contact with the water tank, such that the water tank constitutes a heat source for the organic Rankine cycle machine;

[0075] - A fluid loop in which the working fluid circulates in a closed loop, the fluid loop connecting the expander to the condenser, the condenser to the first pump, the first pump to the evaporator, and the evaporator to the expander;

[0076] A second water reservoir, distinct from the water tank, and a second pump connected to the second water reservoir and the organic Rankine cycle condenser, supply water as a cold source to the organic Rankine cycle condenser.

[0077] For the pressurized water nuclear reactor (PWR) according to the first embodiment, the reactor (PWR) includes a cooling loop comprising a steam generator and a water condenser, the water condenser being immersed in the pool and connected to the steam generator in a closed loop.

[0078] For the pressurized water reactor (PWR) according to the second embodiment, the decay heat removal device present in the primary loop is a liquid / liquid exchanger, and the heat exchange device is a water exchanger immersed in the pool, such that the water contained in the pool cools the water in the primary loop circulating in the liquid / liquid exchanger.

[0079] For the boiling water nuclear reactor (BWR) according to the first embodiment, the reactor (BWR) includes a cooling circuit, the cooling circuit comprising:

[0080] - Primary steam inlet on the pipeline supplying the turbine to the reactor;

[0081] - A water condenser, which is submerged in the water tank and connected to the steam inlet in a closed loop.

[0082] For a pressurized water reactor (PWR) or boiling water reactor (BWR) according to another embodiment, the system for removing decay heat from the reactor core can be a system for depressurizing steam present in the containment shell, and the heat exchange device can be, on the one hand, a water exchanger immersed in the pool or drawing water directly from the pool, and on the other hand, a containment wall condenser that is in direct contact with the steam present in the containment shell of the reactor.

[0083] The second water reservoir is advantageously arranged in a portion below the pool, advantageously arranged on the ground or in the ground.

[0084] The organic Rankine circulating evaporator can be submerged in the pool or located away from the pool.

[0085] The submerged evaporator is preferably a tubular heat exchanger or a plate heat exchanger.

[0086] According to an advantageous embodiment, the reactor further includes a cooling cycle, the cooling cycle comprising:

[0087] -compressor;

[0088] - A condenser, which is connected to the second pump to supply water to the second pump;

[0089] - Expansion components;

[0090] - Air evaporator;

[0091] - A fluid circuit in which the working fluid circulates in a closed loop, the fluid circuit connecting the compressor to the condenser, the condenser to the expansion member, the expansion member to the air evaporator, and the air evaporator to the compressor.

[0092] The cooling cycle condenser is advantageously an organic Rankine cycle condenser.

[0093] The working fluid of the cooling cycle is more preferably the working fluid of an organic Rankine cycle.

[0094] According to an advantageous variation, the shaft of the organic Rankine cycle expander is connected to the shaft of the cooling cycle compressor.

[0095] According to another advantageous variant, the organic Rankine cycle machine and, where applicable, the cooling cycle are arranged in the lower part of the system, below the water tank.

[0096] According to another variation, the reactor may include an injector disposed in the lower part of the system and connected to a second pump disposed in the upper part of the system, the injector being adapted to charge the second pump.

[0097] The reactor preferably includes a battery for electrically starting the first pump, the electrical components of the organic Rankine cycle, and, where applicable, the cooling cycle, as well as the second pump.

[0098] Therefore, this invention first employs a safe passive condenser system that uses a water reservoir or pool immersed in the passive condenser and located at an elevated position (above the reactor core) as a cooling source. This pool is capable of removing decay heat from the reactor core.

[0099] Now, as explained earlier, this architecture depends on the volume of the pool: the cooling time of the pool is proportional to (or directly related to) its volume, and is therefore limited.

[0100] To mitigate this situation, the present invention essentially includes an organic Rankine cycle machine and a supplementary water reservoir separated from the water tank. The energy stored in the water tank is the heat source for the organic Rankine cycle evaporator, and the supplementary water reservoir is directly supplied to the organic Rankine cycle condenser via a dedicated pump to form the cold source for the organic Rankine cycle condenser.

[0101] Therefore, water loss due to evaporation from the pool is compensated by supplying water from a supplementary water reservoir that is advantageously located in the lower part (preferably at ground level) compared to the higher part of the pool.

[0102] The main advantage of placing the cold source on the ground is that it greatly simplifies the civil engineering work required to support and protect the volume of the safe cold source above the nuclear facility, and reduces construction and maintenance costs as well as the costs associated with seismic studies.

[0103] The decay heat removal system according to the present invention differs from existing systems in the following aspects:

[0104] - Compared to existing systems that use air as a cooling source, water guided from the bottom of the supplementary water tank is used as the cooling source for the organic Rankine cycle condenser.

[0105] The water supplied from the supplementary water reservoir can also be advantageously used as a cold source for the condenser of the cooling cycle, which aims to generate cooling power, for example, to cool an organic Rankine cycle expander, thereby ensuring greater autonomy and reliability of the system.

[0106] Therefore, compared with the geometry of existing systems, the main advantage of the system configuration according to the invention is that it uses water supplied at an elevated position to supply the water pool undergoing evaporation as a cold source for the organic Rankine cycle condenser, and advantageously as a cold source for the cooling cycle.

[0107] Therefore, the system configuration according to the invention enables the use of a plate water exchanger as an organic Rankine cycle evaporator, which must undoubtedly be located away from the water tank, but whose volume is much smaller than that of an equivalent powered air condenser. As an example, the convective exchange coefficient of the plate water exchanger is increased by 50 to 100 times relative to a condenser whose fluid is air.

[0108] Using a water exchanger can reduce the condensation pressure of the organic Rankine cycle fluid in the organic Rankine cycle, thereby improving efficiency.

[0109] Using pumped water as the cold source for the organic Rankine cycle, and advantageously as the cold source for the combined cooling cycle, can further greatly improve the reliability of the system: the reduced size of the exchanger makes it less susceptible to external attacks, whether natural or malicious.

[0110] Furthermore, water / water plate condensers are well-known exchangers in the field and have high reliability (a fundamental standard in the nuclear field).

[0111] Therefore, the fact that the cold source of the heat exchanger for the cold source (reactor cooling cycle, organic Rankine cycle, cooling cycle) is water avoids the use of a supplementary cold source, which in the prior art is air.

[0112] As mentioned above, air exchangers are highly dependent on ambient air temperature. Therefore, using water from a reservoir at the bottom of the facility as the cooling source for the organic Rankine cycle makes it less dependent on external temperature and its variations.

[0113] In fact, with this invention, due to the circulating cold source, there are no longer any power limitations. Furthermore, the size of the water exchanger and the temperature conditions on the cold source side are not limited as in prior art air condensers; the aim is to minimize its size without affecting the aforementioned air temperature.

[0114] Therefore, the present invention enables the generation of high electrical power and thus allows a large amount of water to be directed from a lower part to a higher part with a small facility volume.

[0115] Adding a cooling cycle to the organic Rankine cycle according to the invention allows for the cooling of the expander of the organic Rankine cycle as well as other components to be cooled, such as power electronic devices, thus improving the autonomy and reliability of the system. A single condenser can advantageously be shared by the organic Rankine cycle and the cooling cycle, which can be achieved through series or parallel fluid flows.

[0116] The residual power of the organic Rankine cycle according to the present invention can not only meet the above-mentioned needs, but also meet other safety electrical needs of the facility, such as power supply for control, measurement, cooling equipment, etc.

[0117] The system according to the invention implies the use of batteries required to start the system. In fact, the cold source for the organic Rankine cycle is water from a replenishment reservoir, necessitating the activation of a water pump that draws water from the replenishment reservoir to start the system. The energy accumulated in these batteries may be very limited, and redundant multiple battery banks enable extremely high reliability.

[0118] Ultimately, nuclear reactors with systems according to the present invention have many advantages, among which:

[0119] - Significant improvements to existing cooling systems for nuclear reactors, particularly for pressurized water reactors, which include steam generators, natural convection closed-loop circuits, and cooling pools;

[0120] - A reliable and autonomous system;

[0121] - The possibility of a small upper volume for nuclear facilities reduces civil engineering and cost constraints;

[0122] - By using a passive condenser and cold source at a high altitude, the passive design for removing decay heat from the reactor is maintained. Decay heat removal continues to be driven by the gradual evaporation of the cold source and is not entirely dependent on an active system such as an organic Rankine cycle loop. Only the autonomy of the cold source depends on the operation of this active but autonomous system. Therefore, there is no loss of reliability of the decay heat removal function, as is the assumption that all decay heat must depend on an active circuit of the organic Rankine cycle type: [5]

[0123] Other advantages and features of the invention will become more apparent when reading the detailed description of embodiments of the invention, provided only by way of illustrative and non-limiting description. Attached Figure Description

[0124] [ Figure 1 ] Figure 1 The decay heat of a conventional nuclear reactor, known as a VVER TOI reactor, is shown as a curve representing the decrease over time.

[0125] [ Figure 2 ] Figure 2This is a schematic diagram of the passive decay heat removal system of a pressurized water reactor core in the prior art.

[0126] [ Figure 3 ] Figure 3 This is a schematic diagram of a passive system for removing decay heat from a pressurized water reactor core according to one embodiment of the present invention.

[0127] [ Figure 4 ] Figure 4 Is it like this? Figure 3 Ts entropy diagrams of the organic Rankine cycle and cooling cycle of the system.

[0128] [ Figure 5 ] Figure 5 This is a schematic diagram illustrating a first variation of the system according to the invention.

[0129] [ Figure 6 ] Figure 6 This is a schematic diagram illustrating a second variation of the system according to the invention.

[0130] [ Figure 7 ] Figure 7 This is a schematic diagram illustrating a third variation of the system according to the present invention.

[0131] [ Figure 8 ] Figure 8 This is a schematic diagram illustrating another embodiment of the invention, which has a system for depressurizing steam present in the containment of a boiling water reactor or a pressurized water reactor.

[0132] [ Figure 9 ] Figure 9 This is a schematic diagram illustrating a first variation of a heat exchange device according to the invention for a boiling water reactor or a pressurized water reactor.

[0133] [ Figure 10 ] Figure 10 This is a schematic diagram illustrating a first variation of a heat exchange device according to the invention for a boiling water reactor or a pressurized water reactor. Detailed Implementation

[0134] Throughout this application, the terms “vertical,” “low,” “up,” “low,” “high,” “below,” and “above” shall be understood in reference to a water-filled cooling pool of a nuclear reactor arranged in a horizontal operating configuration above the reactor core.

[0135] Figure 1 and Figure 2 As already described above, it will not be discussed further below.

[0136] exist Figures 1 to 10 In this invention, elements identical to those in the prior art are represented by the same reference numerals.

[0137] In relation to the present invention Figures 3 to 7 The image shows only a portion of the system used to cool the core of a pressurized water nuclear reactor, namely the steam generator, which is connected in a closed loop to a water exchanger submerged in a cooling pool.

[0138] Dashed lines represent power lines for various electrical components, while solid lines represent fluid pipelines.

[0139] exist Figure 3 The diagram illustrates an autonomous system according to the invention for removing at least some decay heat from a pressurized water reactor.

[0140] The system first includes a cooling pool 5 arranged above the reactor core and a water condenser 4 immersed in the cooling pool, so that the water contained in the cooling pool cools the steam flowing out from the reactor's secondary loop.

[0141] The system also includes an Organic Rankine Cycle (ORC) machine 6, which comprises:

[0142] - Expander 60;

[0143] - Condenser 61;

[0144] - The first pump 62 is used for the working fluid;

[0145] - Evaporator 63, which is arranged relative to cooling pool 5, such that cooling pool 5 constitutes a heat source for organic Rankine cycle;

[0146] - Fluid circuit 64, in which the working fluid circulates in a closed loop.

[0147] As shown in the figure, according to the present invention, the fluid circuit 64 connects the expander 60 to the condenser 61, connects the condenser 61 to the first pump (referred to as the organic Rankine cycle pump) 62, connects the organic Rankine cycle pump 62 to the evaporator 63, and connects the evaporator 63 to the expander 60.

[0148] The second water reservoir forming the general pool 7 contains all the cold sources dedicated to cooling the reactor and supplies cooling pool 5 dedicated to the organic Rankine cycle and includes safety condenser 4 and organic Rankine cycle evaporator 63.

[0149] Water from the general-purpose pool 7 serves as the cold source for the heat exchanger condenser 61. The water from the general-purpose pool 7 is slightly heated by the condenser 61 before being injected into the cooling pool 5 via a second pump (supply pump 8). This pump 8 supplies a dedicated fluid line 65 to mitigate evaporation in the cooling pool 5, which receives reactor decay heat.

[0150] Expander 60 can typically be a turbine pressure regulator, a spiral pressure regulator, a screw pressure regulator, a piston pressure regulator, etc.

[0151] Condenser 61 is typically a plate condenser.

[0152] Organic Rankine circulating pumps 62 are typically centrifugal pumps, diaphragm pumps, screw pumps, etc.

[0153] The organic Rankine cycle machine 6 may include a buffer tank 66, that is, a reserve of a certain amount of working fluid to enable the organic Rankine cycle to operate particularly well under varying conditions. For example... Figure 3 As shown, the buffer tank 66 can be arranged upstream of the organic Rankine circulation pump 62.

[0154] exist Figure 3 In the embodiment shown, the evaporator 63 is a tubular evaporator vertically immersed in the cooling pool 5.

[0155] The system also includes a second water reservoir 7, which is separate from the cooling pool, and a pump 8 connected to the second water reservoir and the condenser 61 of the organic Rankine cycle to supply water to the condenser 61 as a cold source for the organic Rankine cycle.

[0156] exist Figure 3 In an advantageous embodiment, a cooling cycle 9 is also provided, comprising:

[0157] -Compressor 90;

[0158] - Condenser 61, which is an organic Rankine cycle condenser, is connected to water pump 8 to supply water to water pump 8;

[0159] -Expansion member 92;

[0160] - Air evaporator 93;

[0161] - Fluid circuit 94, in which the working fluid circulates in a closed loop.

[0162] Fluid circuit 94 connects compressor 90 to organic Rankine cycle condenser 61, condenser 61 to expansion member 92, expansion member 92 to air evaporator 93, and air evaporator 93 to compressor 90.

[0163] The expansion member 92 can be a valve, or preferably a turbine, injector, etc.

[0164] Similar to the Organic Rankine Cycle 6, the Cooling Cycle 9 may also include a buffer tank that forms a working fluid reservoir in the cycle.

[0165] A battery 10 can be provided for electrically starting various pumps 62, 8, the electrical components of the organic Rankine cycle, and, where applicable, the cooling cycle 9. More precisely, the battery can be used to start the function of the organic Rankine cycle, that is, to start the organic Rankine cycle pump 62 and activate the submerged pump 8 that supplies the cold source to the cooling pool 5, thereby enabling the provision of the cold source (condenser exchanger) for the organic Rankine cycle.

[0166] The following is a size example for a pressurized water reactor with a rated power of 3200 MWth under accident conditions.

[0167] The working fluid of an organic Rankine cycle is an organic fluid with an evaporation temperature below boiling water, approximately 100°C at atmospheric pressure. Notable examples include Novec 649, HFE 7000, and HFE 7100.

[0168] Many other organic fluids can be envisioned, such as alkanes, HFCs, HFOs, HFCOs, HFEs, and other fluids (NH3, CO2) and all their mixtures.

[0169] The fluid used to simulate the set dimensions is HFE7100, and it is advantageously used for both the organic Rankine cycle 6 and the cooling cycle 9.

[0170] In this example, the temperature sensor or level sensor of the water in cooling pool 5 is able to detect the complete saturation state of cooling pool 5 and the beginning of loss of liquid level due to boiling.

[0171] There is a delay before the filling pump 8 is started, during which the cooling pool 5 is partially emptied. For reliability, the flow rate of pump 8 is fixed at the flow rate of the evaporation loss in the cooling pool at startup.

[0172] Knowing that the remaining power of the reactor core decreases over time, the water level in the cooling pool 5 increases from the moment pump 8 starts.

[0173] Table 1 below summarizes the dimensions associated with the cooling pool.

[0174] [Table 1]

[0175] size value Total volume of pool 5 <![CDATA[1000m 3 ]]> Height of Pool 5 10m The height difference between pool 5 and water storage tank 7 50m

[0176] Table 2 below summarizes information related to the time the pool runs.

[0177] [Table 2]

[0178] Pool operation Duration (h) Pool 5 becomes saturated 1.5 Pool 5 is half-empty / Organic Rankine Cycle 6 is started. 20 Pool 5 was refilled 90

[0179] Table 3 below shows the flow rates:

[0180] [Table 3]

[0181] Flow rate Value (kg / s) Flow rate of the working fluid in an organic Rankine cycle 1 The flow rate of the pumped water (cold source) 6 The flow rate of the cooling circulating working fluid 0.02

[0182] Table 4 below shows the external temperatures:

[0183] [Table 4]

[0184] temperature Value (°C) Average temperature of the heat source 100 Temperature of cold source 30 Temperature of the cold source (exiting the cooling cycle) 30 Temperature of the cold source (exiting the organic Rankine cycle) 38

[0185] Table 5 below shows the internal pressure:

[0186] [Table 5]

[0187] pressure Value (bar) Organic Rankine Cycle 6 High Pressure 2.7 Organic Rankine Cycle 6 Low Pressure 0.5 Cooling cycle 9 high pressure 2.0 Cooling cycle 9 low pressure 0.1

[0188] Table 6 below shows the power of the switch:

[0189] [Table 6]

[0190] power Value (kW) Organic Rankine cycle condenser (61) power 170 Organic Rankine cycle evaporator (63) power 180 Cooling condenser (61) power 3 Cooling evaporator (93) power 2

[0191] Table 7 below shows the electrical power:

[0192] [Table 7]

[0193] Electric power Value (kW) Organic Rankine circulating pump (62) 0.5 Water pump (8) 7.5 Compressor (90) 0.7 Electric turbine (60) 8.6

[0194] Therefore, Table 8 below summarizes the volumes of the switches to be sized under all the above operating conditions: [Table 8]

[0195] volume <![CDATA[Value (m 3 )]]> Organic Rankine cycle condenser volume (HFE7100 / water) 0.01 Cooling cycle condenser volume (HFE7100 / water) 0.0005 Organic Rankine cycle evaporator volume (HFE7100 / water) 0.5

[0196] Ts diagrams for organic Rankine cycle and cooling cycle are shown below Figure 4 As shown.

[0197] Figure 3 One possible variation of the configuration is to connect the shaft 11 of the turbine 60 of the organic Rankine cycle 6 to the shaft of the compressor of the cooling cycle. Figure 5 The configuration shown makes it possible to eliminate the need to supply electrical power to the compressor for the cooling cycle, thus saving energy (electromechanical conversion).

[0198] The second variation of the system combines the advantages of the following components between the organic Rankine cycle and the cooling cycle: working fluid, some piping, and condenser 61, as already shown.

[0199] Another variation of the system places the organic Rankine cycle and cooling cycle in the lower part of the system due to the presence of the intermediate loop. This allows the organic Rankine cycle turbine and the pump 8 used to supply water from the lower part to the upper part to be connected to the same shaft. This improves the system's reliability because the power transfer between the turbine and the pump 8 is purely mechanical: no mechanical energy is converted into electrical energy. However, this configuration, with the organic Rankine cycle located in the lower part, makes it susceptible to many accidental situations, such as flooding. Furthermore, it is necessary to extract heat energy from the lower pool. This also makes maintenance and monitoring by operators more convenient.

[0200] like Figure 6 As shown, the organic Rankine cycle can also be placed in the lower part via an intermediate loop without connecting the water pump 8 to the organic Rankine cycle turbine 60. This intermediate loop includes a supplementary evaporator 67 supplied via a third pump 68. An advantage of this configuration is that organic Rankine cycle functionality can be achieved through auxiliary heat source 12 and valve 13, enabling system maintenance / testing to improve its reliability.

[0201] Another possible variation is not to use Figure 3 Instead of the submerged tubular evaporator shown, a remotely positioned evaporator, such as a plate evaporator, is used. Therefore, it is necessary to... Figure 7 The pump 14 shown supplies water from the reservoir to the piping. This configuration reduces the size of the heat exchanger, the workload of mounting the exchanger on the pool, or, as in the previous configuration, allows the organic Rankine cycle to operate with an auxiliary heat source. It is important to note that the mixing of water at the evaporator outlet with water from the organic Rankine cycle condenser requires only a single intake from the pool, rather than the two intakes in other configurations and variations.

[0202] Another possible variation of this technology involves placing a condensate injector at the lower part of the facility. Thus, by actuating the pumping motion via the lower injector, the water pump 8 can be positioned at the upper part of the structure. This configuration allows the organic Rankine cycle and the entire pump 8 to be located at the upper level (and therefore safer, protected from external intrusion, flooding, etc.). The injector will be able to charge the system: supplied by a low-capacity thermal energy reserve, the injector will introduce a sufficient amount of water into the inlet pipe of the pump 8 to charge it.

[0203] The invention is not limited to the example just described; specific features of the example shown may be combined with each other in variations not shown.

[0204] Other variations and implementations can be conceived without departing from the scope of the present invention.

[0205] The decay heat removal system described above with reference to pressurized water nuclear reactors can be used in boiling water nuclear reactors (BWRs).

[0206] Generally, the present invention is applicable to any pool 5 that can constitute a cold source for cooling the core of a pressurized water reactor or a boiling water reactor, or for cooling and / or depressurizing the main containment of a pressurized water reactor or a boiling water reactor.

[0207] Therefore, although in the example shown, the device for removing decay heat from the reactor core includes a steam generator, the device could also be a condenser installed in the containment, whether for a pressurized water reactor or a boiling water reactor.

[0208] For example, for pressurized water reactors, refer to the ambient condenser panel (“Passive containment heat removal”) of the HPR1000 project or the disclosure [6] which describes an optimized condenser mounted on the containment wall (“Passive containment cooling system”). For boiling water reactors, see the configuration of the containment cooling condenser in the KERENA reactor.

[0209] More generally, for pressurized water reactors or boiling water reactors, the means for removing decay heat from the reactor core can be a system for depressurizing steam present in the containment. Figure 8 The heat exchange device can be submerged in pool 5. Figure 10 The closed-loop configuration in the middle is taken from reference [7]) or water is taken directly from pool 5 ( Figure 9 The closed-loop configuration, taken from reference [7], is a water exchanger 4, and on the other hand, it can be a containment wall condenser 11 that is in direct contact with the steam present in the containment 100 of the reactor.

[0210] Pool 5 can be a source of water for the spray manifolds of the containment spray circuit, which reduces pressure in the event of an accident that would cause a significant increase in pressure within the reactor building, thereby maintaining the integrity of the containment. For pressurized water reactors, see the configuration of the internal spray manifolds inside the main containment of the HPR1000 project or outside the main containment of the AP1000 project.

[0211] List of cited references

[0212] [1]:https: / / www-pub.iaea.org / MTCD / Publications / PDF / TE-1785_web.pdf.

[0213] [2]: S. Kadalev et al., 2014, Annals of Nuclear Energy, Vol. 72, pp. 182-188.

[0214] [3]: D.C. Sun, Y. Li, Z. Xi, Y.F. Zan, P.Z. Li, W.B. Zhuo, “Experimental evaluation of safety performance of emergency passive residual heat removal system in HPR1000”, Nuclear Engineering and Design, Vol. 318, 2017, pp. 54 - 60, ISSN 0029 - 5493, https: / / doi.org / 10.1016 / j.nucengdes.2017.04.003.

[0215] [4]: David Hinds and Chris Maslak, “Next-generation nuclear energy: The ESBWR” Nuclear News. January 2006.

[0216] [5]: Hofer, Buck, Starflinger, “Operational Analysis of a self-propelling Heat Removal System using supercritical CO2 with athlet”, The 4th European sCO2 Conference for Energy Systems March 23 - 24, 2021, Online Conferences sCO2, 2021 - sCO2.eu - 157. [6]: Huiun Ha et al., “Optimal design of passive containment cooling system for innovative PWR” Nuclear Engineering and Technology 49(2017) pp. 941 - 952.

[0217] [7]: https: / / www - pub.iaea.org / MTCD / Publications / PDF / te_164_web.pdf.

Claims

1. A light water nuclear reactor (LWR), comprising: - Reactor core (1); - A system for removing at least some decay heat from the reactor core, the system comprising: A first water storage tank or pool is arranged above the reactor core; a heat exchange device is immersed in the pool, such that the water in the pool cools the steam entering the device from the primary or secondary loop of the reactor. Organic Rankine Cycle (ORC) machine (6), said organic Rankine cycle machine (6) comprising: -Expander (60); - Condenser (61); - First pump (62); - Evaporator (63), the evaporator (63) being arranged in contact with the pool such that the pool constitutes a heat source for the organic Rankine cycle; The organic Rankine cycle fluid loop (64) in which the working fluid circulates in a closed loop, the organic Rankine cycle fluid loop (64) connecting the expander (60) to the condenser (61), the condenser (61) to the first pump (62), the first pump to the evaporator (63), and the evaporator (63) to the expander (60); A second water reservoir (7), different from the water tank, and a second pump (8), the second pump (8) being connected to the second water reservoir and the condenser of the organic Rankine cycle to supply water as a cold source for the organic Rankine cycle to the condenser of the organic Rankine cycle.

2. The nuclear reactor according to claim 1, wherein the nuclear reactor is a pressurized water reactor, comprising a cooling circuit including a steam generator and a water condenser, the water condenser being submerged in the water pool and connected to the steam generator in a closed loop.

3. The nuclear reactor according to claim 1, wherein the nuclear reactor is a pressurized water reactor, the decay heat removal device present in the primary loop is a liquid / liquid exchanger, and the heat exchange device is a water exchanger immersed in the pool, such that the water contained in the pool cools the water in the primary loop circulating in the liquid / liquid exchanger.

4. The nuclear reactor according to claim 1, wherein the nuclear reactor is a boiling water reactor, and includes a cooling circuit, the cooling circuit comprising: - Primary steam inlet on the pipeline supplying the turbine to the reactor; - A water condenser, which is submerged in the water tank and connected to the steam inlet in a closed loop.

5. The nuclear reactor according to claim 1, wherein the nuclear reactor is a pressurized water reactor or a boiling water reactor, the system for removing decay heat from the reactor core is a system for depressurizing steam present in the containment shell (100) of the reactor, and the heat exchange device is a water exchanger (4) immersed in the pool.

6. The nuclear reactor according to claim 1, wherein the nuclear reactor is a pressurized water reactor or a boiling water reactor, the system for removing decay heat from the reactor core is a system for depressurizing steam present in the containment shell (100) of the reactor, and the heat exchange device is formed by a containment wall condenser (11) that draws water directly from the pool (5) on the one hand and is in direct contact with steam present in the containment shell (100) of the reactor on the other hand.

7. The nuclear reactor according to any one of claims 1 to 6, wherein the second water reservoir is arranged in a portion lower than the pool.

8. The nuclear reactor according to claim 1, wherein the evaporator is submerged in the pool or located away from the pool.

9. The nuclear reactor according to claim 8, wherein the evaporator, which is submerged in the pool or located away from the pool, is a tubular heat exchanger.

10. The nuclear reactor according to claim 8, wherein the evaporator, which is submerged in the pool or located away from the pool, is a plate heat exchanger.

11. The nuclear reactor according to claim 1, further comprising a cooling cycle (9), said cooling cycle (9) comprising: - Compressor (90); - A condenser (61) connected to the second pump (8) to supply water to the second pump (8); -Expansion member (92); - Air evaporator (93); - The fluid circuit (94) of the cooling cycle (9) in which the working fluid circulates in a closed loop, the fluid circuit (94) of the cooling cycle (9) connects the compressor (90) to the condenser (61), the condenser (61) to the expansion member (92), the expansion member (92) to the air evaporator (93), and the air evaporator (93) to the compressor (90).

12. The nuclear reactor according to claim 11, wherein the condenser (61) of the cooling cycle is the condenser of the organic Rankine cycle.

13. The nuclear reactor according to claim 11, wherein the working fluid of the cooling cycle is the working fluid of the organic Rankine cycle.

14. The nuclear reactor according to claim 11, wherein, The shaft of the expander in the organic Rankine cycle is connected to the shaft of the compressor in the cooling cycle.

15. The nuclear reactor of claim 11, wherein the organic Rankine cycle and, where applicable, the cooling cycle are arranged in the lower part of the system, below the pool.

16. The nuclear reactor of claim 1, comprising an injector disposed in the lower part of the system and connected to the second pump disposed in the upper part of the system, the injector being adapted to charge the second pump.

17. The nuclear reactor of claim 11, comprising a battery for electrically starting the first pump, electrical components of the organic Rankine cycle and, where applicable, electrical components of the cooling cycle, and the second pump.

18. The nuclear reactor according to claim 1, wherein the nuclear reactor is a pressurized water reactor (PWR) or a boiling water reactor (BWR).

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