Nuclear Furnace Structure

Abstract

The present invention relates to a reactor structure having an upper compartment above the reactor compartment, wherein the reactor compartment is separated from the upper compartment by a radiation shield, wherein a molten salt reactor (MSR) is located within the reactor compartment, and the MSR comprises a reactor vessel having a reactor vessel lid assembly comprising a reactor vessel lid shield and a reactor vessel lid, and a lifting element is located within the reactor structure, the lifting element comprising at least one bar substantially vertical and axially adjustable along the longitudinal axis by a drive mechanism located within the upper compartment, at least one through-hole for at least one bar provided in the radiation shield, and the reactor vessel lid shield has at least one receiving structure configured to engage and lock with at least one bar. The present invention also relates to a method for performing maintenance work within the reactor compartment, and to a power barge comprising at least one reactor structure.

Description

Technical Field

[0001] The present invention relates to a reactor structure for accommodating a nuclear reactor and means for maintaining the nuclear reactor. The present invention also relates to a method of maintaining a nuclear reactor, such as replacing graphite elements in a reactor vessel. This reactor structure and method enable maintenance to be performed while minimizing radiation exposure to electronic equipment required for maintenance.

Background Art

[0002] A nuclear reactor provides heat generated by a nuclear fission reaction, and this heat is generally utilized by a steam turbine generator to generate electric power used, for example, in industrial processes such as households, hydrogen production, and desalination. The nuclear fission process takes place in a reactor core equipped with nuclear fuel containing fissionable isotopes that undergo fission, such as U-235, Pu-239, etc. The nuclear fuel is usually a solid fuel such as UOx (uranium oxide) in powder / tablet form and is inserted into fuel rod tubes made of a metal alloy or ceramic. Other fuel types are also being studied, and molten salt reactors (MSRs) using molten salts containing dissolved fissionable isotopes have been the subject of decades of research and development that have been activated since initial tests at Oak Ridge National Laboratory (ORNL) in the 1950s and 1960s. Substances other than nuclear fuel also exist in the reactor core. In the case of a thermal nuclear reactor, a moderator is used to reduce the speed of the generated neutrons and suppress the kinetic energy to an energy level at which the probability of nuclear fission occurring, for example, with respect to U-235, is significantly higher. The moderator may be water (light water) as in a boiling water reactor (BWR) or a pressurized water reactor (PWR), or heavy water as in a Canadian deuterium uranium reactor (CANDU-reactor). The moderator may be a graphite structure as in, for example, an RBMK-type reactor or some of various MSR reactors. The graphite moderator structure is often a large and bulky structure that is partitioned, for example, into graphite columns. Graphite tiles may be used as a coating material for a metal alloy reactor vessel.

[0003] Regardless of the type of reactor, core maintenance is necessary and is part of reactor operation. Solid fuel rods are typically replaced every 18 to 24 months. The graphite structure within the core degrades under high radiation and requires replacement every 2 to 10 years, depending on the power density within the core, which requires access to the high-radiation environment of the core.

[0004] Document WO2022 / 017878 discloses a lifting device used for maintenance and refueling of reactors having a reactor pressure vessel (RPV) corresponding to PWRs and BWRs. This lifting device lifts the reactor vessel lid, including the control rods (integrated head assembly, IHP), allowing access to the open reactor core. The lifting mechanism engages with the underside of the closure head assembly and lifts the head assembly by pushing from below with a lifting element such as a lifting jack. [Overview of the Initiative]

[0005] The objective of the present invention is to provide a reactor structure that enables a variety of maintenance operations in an open reactor core.

[0006] A further object of the present invention is to provide a reactor structure having a lifting element for lifting a reactor vessel lid assembly, the lifting element avoiding the need for electrical components to be permanently installed within the reactor compartment.

[0007] A further object of the present invention is to provide a reactor structure particularly suitable for integration with offshore structures.

[0008] According to one aspect of the invention, a reactor structure is provided which includes an upper compartment above the reactor compartment, and the reactor compartment is separated from the upper compartment by a radiation shield. A molten salt reactor (MSR) is located within the reactor compartment, and the MSR is, - Reactor vessel lid shield and reactor vessel lid A reactor vessel having a reactor vessel lid assembly equipped with The lifting element is located within the reactor structure, and the lifting element is, - A drive mechanism located within the upper compartment, substantially vertical, with at least one bar that is axially adjustable along the longitudinal axis. Equipped with, The radiation shield is provided with at least one through-hole for at least one bar, and the reactor vessel lid shield has at least one receiving structure configured to engage and lock with at least one bar.

[0009] According to another aspect of the invention, a method for performing maintenance work in a reactor compartment as described in any one of claims 1 to 12: The steps include: engaging and locking at least one bar to the reactor vessel lid shield and engaging the drive mechanism of the bar to lift the reactor vessel lid shield and open the reactor vessel from above; At least one trolley with a hoist is positioned on at least one transverse beam, at least one transverse beam drive unit is positioned on at least one transverse beam, and at least one trolley with a hoist, transverse beam drive unit, and at least one transverse beam are included in the gantry crane, the at least one transverse beam extending from a first wall of the reactor compartment to a second wall of the reactor compartment opposite the first wall, and the at least one transverse beam is attached to gantry crane rails on the first wall and the second wall, the arrangement is, The steps include opening a reactor compartment hatch to separate the upper compartment from the reactor compartment, lowering at least one hoisted trolley and at least one crossbeam drive unit from the upper compartment through the opened reactor compartment hatch, and connecting at least one hoisted trolley to at least one crossbeam; The steps include: positioning at least one hoisted trolley above the area to be maintained; The steps include: performing maintenance by lowering maintenance equipment to the vicinity of the work area to be maintained; A method including this is provided.

[0010] According to another aspect of the invention, a power barge is provided comprising at least one reactor structure according to any one of claims 1 to 12 for generating heat produced by a nuclear fission reaction, and at least one steam turbine generator for generating electricity using the generated heat.

[0011] Detailed explanation The reactor structure includes an upper section above the reactor compartment, and the reactor compartment is separated from the upper section by a radiation shield. A molten salt reactor (MSR) is located within the reactor compartment, and the MSR is, - Reactor vessel lid shield and reactor vessel lid A reactor vessel having a reactor vessel lid assembly, The lifting element is located within the reactor structure, and the lifting element is, - A drive mechanism located within the upper compartment, substantially vertical, with at least one bar that is axially adjustable along the longitudinal axis. Equipped with, At least one through-hole for at least one bar is provided in the radiation shield, and the reactor vessel lid shield has at least one receiving structure configured to engage and lock with at least one bar.

[0012] How to perform maintenance work: The steps include: engaging and locking at least one bar with the reactor vessel lid shield and engaging the drive mechanism of the bar to lift the reactor vessel lid shield and open the reactor vessel from above; The steps include: positioning at least one trolley with a hoist on at least one transverse beam, and positioning at least one transverse beam drive unit on at least one transverse beam, wherein the at least one trolley with a hoist, the transverse beam drive unit, and the at least one transverse beam are included in a gantry crane, the at least one transverse beam extends from a first wall of the reactor compartment to a second wall of the reactor compartment opposite the first wall, and the at least one transverse beam is attached to gantry crane rails on the first wall and the second wall, and the arrangement is The steps include: opening the reactor compartment hatch to separate the upper compartment from the reactor compartment; lowering at least one hoisted trolley and at least one crossbeam drive unit from the upper compartment through the opened reactor compartment hatch; and connecting at least one hoisted trolley and at least one crossbeam drive unit to at least one crossbeam; The steps include: positioning at least one hoisted trolley above the area to be maintained; The steps include: performing maintenance procedures by lowering maintenance equipment to the vicinity of the work area to be maintained; Includes.

[0013] The power barge comprises at least one reactor structure according to any one of claims 1 to 12 for generating heat produced by a nuclear fission reaction, and at least one steam turbine generator for generating electricity using the generated heat.

[0014] The reactor structure and maintenance method according to the present invention have been found to have numerous advantages. At least one bar is a mechanical device without electrical components and can be used in the high-radiation environment of the reactor compartment during maintenance work without degrading its function as part of the lifting element. The bar is controlled by a drive mechanism located in the upper chamber outside the reactor compartment and protected by a radiation shield. Furthermore, engagement and locking of the bar to the reactor lid shield is performed without the use of electronic equipment, for example, by inserting the end of the threaded bar into the threads of the lid shield, thereby locking the threaded bar to the lid in a manner similar to a nut and bolt configuration.

[0015] After the lifting element lifts the lid and the reactor core is opened for maintenance work, more practical equipment is brought into the reactor chamber. This reduces radiation exposure because equipment such as gantry cranes are not permanently installed inside the reactor chamber.

[0016] Radiation-sensitive components and other equipment of the gantry crane are brought into the reactor chamber from the external environment via an airlock, and exposure to radiation within the upper chamber during the placement of gantry crane components is minimized by passing them through a small sealed hatch between the upper chamber and the reactor chamber.

[0017] reactor structure In one embodiment, the reactor structure includes an upper compartment above the reactor compartment, and the reactor compartment is separated from the upper compartment by a radiation shield. A molten salt reactor (MSR) is located within the reactor compartment, and the MSR is, - Reactor vessel lid shield and reactor vessel lid A reactor vessel having a reactor vessel lid assembly equipped with The lifting element is located within the reactor structure, and the lifting element is, - A drive mechanism located within the upper compartment, substantially vertical, with at least one bar that is axially adjustable along the longitudinal axis. comprising At least one through hole for at least one bar is provided in the radiation shield, and the reactor vessel head shield has at least one receiving structure configured to engage and lock with at least one bar.

[0018] A molten salt reactor (MSR) is often based on achieving a critical state with a fissile material contained within a reactor vessel, which often dissolves in a molten salt and typically also contains the reactor core. When an MSR uses a fissile material dissolved in a molten salt, the salt is referred to as the fuel salt (or molten fuel salt). Another type of reactor in which a molten salt is used as a coolant to accommodate temperature rises in solid pebble fuel, where the fuel is solid and often TRISO-type fuel, is also referred to as an MSR. Such a reactor is described in US8442182, where a molten salt is used as a coolant for pebble fuel immersed in the coolant.

[0019] In one embodiment, the fuel salt is a fluoride fuel salt or a chloride fuel salt.

[0020] The reactor vessel includes a reactor vessel head assembly for closing, and preferably sealing, the upper opening of the reactor vessel. This assembly may include reactivity control means such as, for example, one or more control rods.

[0021] The reactor vessel head assembly may include a heat exchanger system or a part of a heat exchanger system. The heat exchanger system may include a primary heat exchanger that transfers heat from the nuclear fission process in the molten salt in the core to a secondary coolant salt, and then the heat of the secondary coolant salt is transferred to a medium that powers a turbine system. Such a medium is typically steam, and the turbine system can be used to drive a generator to generate electricity. Other media may be CO2 or helium. A part of the heat exchanger system within the reactor vessel head assembly may be the part that transfers heat from the nuclear fission process in the molten salt in the core to the secondary coolant salt, and the coolant salt is led out of the reactor vessel via a conduit to other parts of the heat exchanger system.

[0022] In one embodiment, the reactor vessel lid assembly comprises an upper plenum, the upper plenum including part of a heat exchanger system.

[0023] The reactor vessel lid shield has the primary function of protecting against radiation inside the reactor vessel, such as gamma rays, and is attached to the reactor vessel lid. Both the reactor vessel lid shield and the reactor vessel lid may include alloys such as stainless steel alloy or nickel-based alloy as structural materials.

[0024] The lifting elements within the reactor structure have the function of lifting the reactor vessel lid assembly to expose the interior of the reactor vessel for maintenance work, and the function of reinstalling the reactor vessel lid assembly after the maintenance work. Other functions of the lifting elements may be performed during the commissioning and decommissioning phases of the MSR. The lifting elements comprise at least one bar that is substantially vertical and axially adjustable along the longitudinal axis by a drive mechanism located in the upper compartment. Thus, at least one bar is preferably in a vertical position within the reactor structure along the longitudinal axis of the bar, both during lifting work and when not being used for lifting work.

[0025] At least one bar is fitted through a through-hole in the radiation shield so that a lifting operation can be performed by the bar moving substantially vertically through the through-hole. The bar fits tightly into the through-hole so that the bar is movable by the use of a drive mechanism located within the upper compartment, while the through-hole is adequately leak-proof. This tight fit can be provided by using a steel O-ring or similar through-hole lining.

[0026] In one embodiment, the lifting element comprises two bars.

[0027] In one embodiment, the lifting element comprises three bars.

[0028] In one embodiment, the lifting element comprises four bars.

[0029] In one embodiment, the lifting element comprises five bars.

[0030] In one embodiment, the lifting element comprises six bars.

[0031] To lift the reactor vessel lid assembly, the outer surface of the reactor vessel lid shield has at least one receiving structure configured to engage and lock with at least one bar. After the bar is locked with the reactor vessel lid assembly, it is ready to begin the lifting operation of the reactor vessel lid assembly. The reactor vessel lid assembly may be pressed tightly against the lower edge of the reactor vessel shield due to the effect of its large weight, and the reactor vessel lid assembly may have an outer shape that locks into a conforming outer shape of the reactor vessel shield edge.

[0032] In one embodiment, the bar is a threaded bar, the first end of which can engage with the threads of a drive mechanism in the upper compartment, and the second end of which can engage and lock the threaded bar with the threads of a receiving structure of a reactor vessel lid shield.

[0033] When a threaded bar engages and locks with the threads of a reactor vessel lid shield, it is understood that these threads are complementary to the threads of the threaded bar, similar to how the threads of a bolt engage with the threads of a nut in a bolt / nut pair.

[0034] The use of threaded joints between the bar and the reactor vessel lid shield has the advantage of providing a high-strength, precise fit that can withstand the gravitational force when lifting the reactor vessel lid assembly, which includes the reactor vessel lid shield and other heavy components of the reactor vessel lid assembly.

[0035] The threaded bar may engage and lock with the threads of the receiving structure of the reactor vessel lid shield, as follows: The threaded bar is lowered toward the threads of the receiving structure by rotating the threads of the drive mechanism using a drive mechanism in the upper compartment, and the threads of the drive mechanism engage with the threaded bar. When the threads of the drive mechanism are engaged with the threaded bar as described above, the threads, for example, which are part of a nut structure, surround and engage with the threads of the threaded bar, and the bar becomes the bolt portion in a nut / bolt pair. The effect of rotating the threads of the drive mechanism is that the threaded bar moves along its longitudinal axis by translation rather than rotation. When the threaded bar reaches the threads of the receiving structure, the threaded bar needs to rotate into the threads of the receiving structure so that it is fixed in the threads of the receiving structure. This rotation can be performed, for example, by conventional methods, by the bar itself rotating within the drive mechanism. Alternatively, this rotation can be achieved by locking the threads of the drive mechanism in the appropriate position with a threaded bar, and then rotating the threads of the drive mechanism, which are in a locked relationship, causing the threaded bar to rotate.

[0036] In one embodiment, the lifting element is selected from the group consisting of rack and pinion, lifting jack, ram / piston, telescoping linear actuator, and rigid chain actuator.

[0037] When a rack and pinion is selected as the lifting element, the bar functions as the rack; when a lifting jack is selected as the lifting element, the bar functions as the cylinder; and when a ram / piston is selected as the lifting element, the bar functions as the piston rod. Regardless of the lifting element selected, the bar can engage and lock with the reactor vessel lid shield.

[0038] In one embodiment, the bar is equipped with a foldable forklift.

[0039] The folding forklift preferably forms one end of a bar to engage and lock with the reactor vessel lid shield. When the bar with the closed forks is lowered into the receiving structure of the reactor vessel lid shield, the closed forklift opens and the forks lock with the receiving structure.

[0040] In one embodiment, the reactor structure includes an airlock within the upper compartment, the airlock comprising an upper compartment hatch that separates the upper compartment from the external environment, and at least one reactor compartment hatch that separates the upper compartment from the reactor compartment.

[0041] In one embodiment, at least one reactor compartment hatch has a size with a minimum dimension of less than 1.5 m, for example less than 1 m, for example less than 0.5 m. Preferably, there are more reactor compartment hatches, such as two hatches, with one hatch positioned above one location in the storage area and the other hatch positioned above another location in the storage area. One hatch may be used, for example, to lower equipment for a gantry crane, and another hatch may be used to lower a camera into the reactor compartment to guide the equipment into place.

[0042] The largest portion of the equipment for maintenance is already located within the reactor compartment, and the only items that need to be introduced into the reactor compartment from the upper compartment are equipment such as trolleys with hoists and attachable gripping tools. Other items that need to be introduced through the hatch are graphite moderator structures, such as graphite moderator columns and fuel tubes, all of which have small minimum dimensions. Therefore, the reactor structure according to this embodiment can have a reactor compartment hatch with relatively small minimum dimensions, which is advantageous because the area surrounding the hatch opening generally represents a safety risk.

[0043] In one embodiment, the reactor structure includes storage areas within the reactor compartment for spent graphite moderator, spent graphite shield, and spent fuel tubes.

[0044] The storage area for exposed materials is advantageously located within the reactor compartment, shielded from the surroundings by a shielding wall and radiation shield that separates the reactor compartment from the upper compartment. Other items to be stored may be equipment and tools used for maintenance work, for example, if the equipment and tools have received radiation levels that require preservation for the subsequent decommissioning process along with the reactor.

[0045] In one embodiment, the reactor structure includes a gantry crane within the reactor compartment comprising at least one transverse beam, a transverse beam drive unit, and a trolley with a hoist, wherein the at least one transverse beam extends from a first wall of the reactor compartment to a second wall of the reactor compartment opposite the first wall, and the at least one transverse beam is attached to gantry crane rails on the first and second walls.

[0046] Conventional gantry cranes are suitable for work inside the reactor vessel. The thick inner walls of the reactor compartment, and preferably the gantry crane rails which are part of the internal or surface wall structure of the reactor compartment wall, provide strong support to one or more crossbeams of the gantry crane, allowing for the use of relatively narrow reactor compartments. The crossbeam drive is sometimes conventionally referred to as the bridge drive. A trolley with a hoist includes both a hoist drive and a trolley drive.

[0047] In one embodiment, the reactor structure includes a gantry crane within the reactor compartment, comprising a transverse beam, a transverse beam drive unit, and a trolley with a hoist, the transverse beam extending from a first wall of the reactor compartment to a second wall of the reactor compartment opposite the first wall, and attached to gantry crane rails on the first and second walls.

[0048] When a gantry crane has a single crossbeam, the trolley with hoist can be mounted on the underside of the crossbeam, preferably where the crossbeam has an I-beam shape, and the trolley has an outer shape that locks into the underside of the I-beam. Preferably, the trolley with hoist is mounted on the upper side of the crossbeam.

[0049] In one embodiment, the reactor structure includes a gantry crane within the reactor compartment, comprising two transverse girders, a transverse girder drive unit, and a trolley with a hoist, wherein the transverse girders extend from a first wall of the reactor compartment to a second wall of the reactor compartment opposite the first wall, and the two transverse girders are attached to gantry crane rails on the first and second walls.

[0050] By using two crossbeams, the lifting capacity can be increased compared to a gantry crane with one crossbeam, which is suitable for large reactor vessel lid assemblies. The hoisted trolley is supported by both crossbeams, preferably between two crossbeams having an I-beam shape, and as the trolley moves, it is supported by the lower part of the I-beam shape.

[0051] The reactor vessel lid assembly may include reactivity control means, such as one or more control rods. The reactivity control means includes a control rod drive mechanism in the upper compartment. The drive rod of the drive mechanism passes through the vessel lid shield and is connected to the control rods housed in the reactor core, thereby allowing absorption of neutron radiation in the core to control the fission reaction. The drive rod in the control rod drive mechanism can raise and lower the control rods in the reactor core.

[0052] In one embodiment, the reactor vessel lid assembly comprises a reactivity control means, which comprises at least one control rod that is axially adjustable along the longitudinal axis of at least one control rod and connected via at least one drive rod to a control rod drive mechanism located in the upper compartment, the mechanism being fixed to a separation portion of the radiation shield, the portion being fixed to the upper side of the reactor vessel lid shield by a vertical spacer structure.

[0053] One advantage of the above embodiment is that the drive rod remains engaged with the control rod drive mechanism throughout the entire lifting procedure for raising the reactor vessel lid. Therefore, there is no need for a separate procedure to detach the drive rod from the drive unit before lifting the lid and to reattach the drive rod to the drive unit after the reactor lid has been lowered back into place on the reactor vessel.

[0054] In one embodiment, the vertical spacer structure is a closed structure that surrounds at least a portion of the reactivity control means.

[0055] When the reactor vessel lid assembly is raised to the upper position along with the reactivity control means, these control means are positioned within the upper compartment, and a closed vertical spacer structure is used to shield the reactivity control means in order to reduce radiation within the upper compartment.

[0056] In one embodiment, the vertical spacer structure is a lattice structure.

[0057] In one embodiment, the reactor vessel lid assembly is - Reactor vessel lid shield, -Reactor vessel lid, - Upper reactor plenum, and - Reactivity control means It includes integrated units, such as mechanically integrated units.

[0058] Maintenance work is advantageous if the reactor vessel lid assembly is an integrated unit and the entire assembly can be lifted in a single lifting operation. For example, if the heat exchanger in the upper plenum is connected to piping, or if there is a second heat exchanger outside the reactor vessel or outside the reactor compartment, various parts of the reactor vessel lid assembly may need to be separated before the lifting operation. After separation, the entire reactor vessel lid assembly can be lifted.

[0059] In one embodiment, the reactor vessel lid shield and the reactor vessel lid are an integrated unit, and for example, the reactor vessel lid is formed by the lower surface of the reactor vessel lid shield.

[0060] In one embodiment, the reactor structure is sealed off from the external environment.

[0061] The arrangement of elements within the reactor structure ensures that all elements are positioned relatively close to each other. For example, the reactor vessel is adjacent to the storage area, which has the effect of giving the reactor structure a relatively small surface area facing the external environment. The radiation shield between the reactor compartment and the upper compartment also benefits from the close positioning of these two elements. A relatively compact reactor structure results in a cost-effective structure for sealing off from the external environment.

[0062] In one embodiment, the reactor structure includes a drain tank for storing molten salt.

[0063] A drain tank can be used to store salt before the reactor starts operation, or as a safety system using a molten salt plug as described in the prior art, and molten fuel salt containing fissile material is discharged into the drain tank to stop the nuclear reaction or to cool the molten salt.

[0064] In one embodiment, the offshore structure, preferably a power barge, comprises at least one reactor structure for generating heat produced by a nuclear fission reaction, and at least one steam turbine generator for generating electricity using the generated heat.

[0065] The reactor structure is particularly well-suited as part of offshore structures such as barges, where space minimization is a critical requirement. The arrangement of elements within the reactor structure ensures that all elements are relatively close to one another; for example, the reactor vessel is adjacent to the storage area. The radiation shield between the reactor compartment and the upper compartment also benefits from this close arrangement of elements. The upper compartment may function as a dry area, for example, mounted on an offshore structure such as a barge.

[0066] In one embodiment, the radiation shield separating the upper compartment from the reactor compartment is, for example, part of the bulkhead of an offshore structure such as a barge.

[0067] The integration of the reactor structure with the offshore structure, preferably a barge, can be advantageously achieved by having the radiation shield separating the upper compartment from the reactor compartment form part of the bulkhead of the offshore structure, resulting in space savings by utilizing the radiation shield both as a radiation shield and as a bulkhead of the offshore structure. When the radiation shield is part of the bulkhead of the barge, the bulkhead extends substantially from one end of the barge side to the other, covering substantially the entire width of the barge, and preferably 3 to 10 meters, for example 5 to 8 meters, above sea level. The aforementioned portion of the bulkhead that also functions as a radiation shield may be located near the middle of a line that crosses the width of the barge, or two reactor structures may be positioned side by side along the line, both utilizing the bulkhead as a radiation shield.

[0068] In one embodiment, a method for performing maintenance work in a reactor compartment according to any one of claims 1 to 12: The steps include: engaging and locking at least one bar to the reactor vessel lid and engaging the drive mechanism of the bar to lift the reactor vessel lid shield and open the reactor vessel from above; The steps include: positioning at least one trolley with a hoist on at least one transverse beam, and positioning at least one transverse beam drive unit on at least one transverse beam, wherein the at least one trolley with a hoist, the transverse beam drive unit, and the at least one transverse beam are included in a gantry crane, the at least one transverse beam extends from a first wall of the reactor compartment to a second wall of the reactor compartment opposite the first wall, and the at least one transverse beam is attached to gantry crane rails on the first wall and the second wall, and the arrangement is The steps include: opening the reactor compartment hatch to separate the upper compartment from the reactor compartment; lowering at least one hoisted trolley and at least one crossbeam drive unit from the upper compartment through the opened reactor compartment hatch; and connecting at least one hoisted trolley and at least one crossbeam drive unit to at least one crossbeam; The steps include: positioning at least one hoisted trolley above the area to be maintained; The steps include: performing maintenance procedures by lowering maintenance equipment to the vicinity of the work area to be maintained; A method including this is provided.

[0069] At the start of maintenance work, the lifting elements raise the reactor vessel lid assembly to a sufficient height vertically above the reactor vessel, allowing the gantry crane to perform maintenance without colliding with the lifted reactor vessel lid assembly. Therefore, the reactor vessel lid assembly needs to be lifted to at least above the gantry crane rails, for example, so that at least the lower surface of the reactor vessel lid assembly is at least 1 meter or at least 3 meters above the gantry crane rails. The reactor vessel lid assembly may also be lifted upward until it contacts the lower surface of the radiation shield. Preferably, depending on the detailed design of the MSR required by the MSR operating license, the reactor is shut down or the fission reaction is stopped by known means. After the reactor vessel lid is removed, preferably before performing the remaining steps of the maintenance work, the radiation intensity is reduced.

[0070] The opening of the reactor compartment hatch may be performed by a motor drive and controlled from the upper compartment.

[0071] The placement of at least one trolley with a hoist on at least one crossbeam may be guided using a camera in the upper compartment or a camera lowered into the reactor compartment, viewed through an open reactor compartment hatch. Similarly, the placement of the crossbeam drive unit may also be guided using a camera as described above. The equipment, such as the trolley hoist, may be attached to one end of a wire, with the other end of the wire connected to a lifting mechanism in the upper compartment, such as a crane, and the equipment is then lowered through an open reactor compartment hatch.

[0072] After the hoisted trolley and crossbeam drive unit are in place, the gantry crane is ready for maintenance work. This work may require various maintenance equipment, such as gripper tools for fuel rods. An example of a prior art gripper is shown in US Patent No. 4903281. Other equipment may include cameras or radiation measuring devices used during maintenance periods to ensure proper maintenance.

[0073] In one embodiment, maintenance work is performed inside the upper plenum.

[0074] In one embodiment, the MSR comprises at least one graphite moderator structure, and maintenance work involves replacing at least one graphite moderator structure within the MSR.

[0075] The replacement of the graphite moderator structure is performed by positioning a hoisted trolley above the graphite moderator structure and lowering the gripper tool to grasp the spent graphite moderator structure. The spent graphite moderator structure is then transported by the hoisted trolley to a storage area, lowered into the storage area for storage, and the release mechanism of the gripper tool is activated. The hoisted trolley is then stopped in a position that allows the introduction of the unused graphite moderator structure through the open reactor compartment hatch without colliding with the gantry crane. After the unused graphite moderator structure is positioned in the appropriate location within the reactor compartment, the hoisted trolley is positioned to engage with the unused graphite moderator structure with the gripper to firmly grasp it, transport it above the reactor, and lower it to the required location within the reactor. The replacement described here can be guided via cameras introduced into the reactor compartment.

[0076] In one embodiment, a maintenance procedure 1 involves the replacement of multiple graphite moderator structures, for example, the replacement of all graphite moderator structures is performed in the maintenance procedure 1.

[0077] Some or all of the graphite moderator structures may be mechanically connected as a single structure, which is preferably done first when constructing the reactor core before the nuclear fission reaction begins. In this embodiment, high lifting capacity is required, and it is preferable to use a gantry crane with at least two crossbeams.

[0078] In one embodiment, the MSR comprises at least one fuel salt pipe, the at least one fuel salt pipe preferably made of graphite, and maintenance work is the replacement of at least one fuel salt pipe.

[0079] The fuel salt tube may be made of an alloy such as a Zr-based, Ni-based, or Mo-based alloy, or of silicon carbide or graphite, and the salt fuel tube contains fuel salts containing fissile material.

[0080] In one embodiment, a reactor structure is provided in which an upper compartment is located above the reactor compartment, and the reactor compartment is separated from the upper compartment by a radiation shield. A pressurized water reactor (PWR) or boiling water reactor (BWR) is located within the reactor compartment, and the PWR or BWR is, - Reactor vessel lid shield and reactor vessel lid A reactor vessel having a reactor vessel lid assembly equipped with The lifting element is located within the reactor structure, and the lifting element is, - A drive mechanism located within the upper compartment, substantially vertical, with at least one bar that is axially adjustable along the longitudinal axis. Equipped with, The radiation shield is provided with at least one through-hole for at least one bar, and the reactor vessel lid shield has at least one receiving structure configured to engage and lock with at least one bar, preferably the bar being a threaded bar, wherein the first end of the threaded bar can engage with the threads of a drive mechanism in the upper compartment, and the second end of the bar can engage and lock the threaded bar with the threads of the receiving structure of the reactor vessel lid shield.

[0081] All features described in any of claims 3 to 10 are applicable to the above embodiments of a PWR or BWR.

[0082] In one embodiment, a method for performing maintenance work in the reactor compartment of a PWR or BWR as described in the above embodiment: The steps include: engaging and locking at least one bar to the reactor vessel lid and engaging the drive mechanism of the bar to lift the reactor vessel lid shield and open the reactor vessel from above; The steps include: positioning at least one trolley with a hoist on at least one transverse beam, and positioning at least one transverse beam drive unit on at least one transverse beam, wherein the at least one trolley with a hoist, the transverse beam drive unit, and the at least one transverse beam are included in a gantry crane, the at least one transverse beam extends from a first wall of the reactor compartment to a second wall of the reactor compartment opposite the first wall, and the at least one transverse beam is attached to gantry crane rails on the first wall and the second wall, and the arrangement is The steps include: opening the reactor compartment hatch to separate the upper compartment from the reactor compartment; lowering at least one hoisted trolley and at least one crossbeam drive unit from the upper compartment through the opened reactor compartment hatch; and connecting at least one hoisted trolley and at least one crossbeam drive unit to at least one crossbeam; The steps include: positioning at least one hoisted trolley above the area to be maintained; The steps include: performing maintenance procedures by lowering maintenance equipment to the vicinity of the work area to be maintained; A method including this is provided.

[0083] In one embodiment, the method described in the above embodiment involves replacing spent fuel rods in a PWR or BWR with unused fuel rods. [Brief explanation of the drawing]

[0084] The present invention will be described in more detail below with reference to schematic diagrams and examples.

[0085] [Figure 1] This image shows a front view of the reactor structure with the reactor vessel lid in its proper position. [Figure 2] The reactor vessel lid is lifted, revealing the reactor structure with its gantry crane from the front. [Figure 3] The reactor vessel lid is lifted, and the reactor structure, including the gantry crane and storage area, is shown from the side. [Figure 4]The image shows a top view of the reactor structure with the reactor vessel lid lifted and a gantry crane. [Figure 5] This image shows a front view of the reactor structure with the reactor vessel lid in its proper position. [Figure 6] The reactor vessel lid is lifted, revealing the reactor structure with its gantry crane from the front. [Explanation of Symbols]

[0086] 1 Reactor structure 2 Upper section 3. Reactor compartment 4. Radiation shield 5. Molten Salt Reactor (MSR) 6 Reactor vessel 7. Reactor vessel lid assembly 8. Reactor vessel lid shield 9 Reactor vessel lid 10 Upper reactor plenum 11 Reactivity control means 12 Lifting Elements 13 Bar 14. Drive mechanism 15 through holes for bars 16 Acceptance Structure 17 Threaded bar 18 The first end of the bar 19 Screw threads of the drive mechanism 20 The second end of the bar 21 Threads of the receiving structure 22 Airlock in the upper compartment 23 Upper compartment hatch 24 Reactor Compartment Hatch 25 Storage area 26 Gantry Cranes 27 crossbeam 28 Trolley with hoist 29 Gantry crane rails 30 The first wall 31 The Second Wall 32 control rods 33 Drive Rod 34 Control rod drive mechanism 35 Separation section of radiation shield 36 Vertical Spacer Structure 37 Drain Tank 38 Graphite Moderator Structure 39 Fuel salt pipe

[0087] The present invention is not limited to the embodiments described in the drawings. Therefore, where reference numerals are used to designate features mentioned in the appended claims, such numerals are included solely for the purpose of enhancing the understanding of the claims and should be understood not in any way as limiting the claims.

[0088] As used herein and in the claims, the expression “comprising” means “constituting at least a part of.” When interpreting any statement containing the expression “comprising” in this specification and in the claims, other characteristics may also exist in each statement in addition to the characteristics indicated by this expression. Related expressions such as “comprise” and “comprised” are interpreted similarly.

[0089] Detailed explanation Herein, the present invention will be described in the following non-limiting examples with reference to the accompanying drawings.

[0090] The reactor structure 1 of the present invention is shown in Figure 1 as a cross-sectional view along AA showing the front of the reactor structure 1. In Figure 1, the reactor lid is in place. Figure 1 shows the reactor structure 1 having an upper compartment 2 above the reactor compartment 3, with compartments 2 and 3 separated by a radiation shield 4. Two bars 13, which are part of a lifting element, are shown, each having a first end 18 that engages with a drive mechanism 14 installed on the floor of the radiation shield 4 in the upper compartment 2. A total of four bars 13 exist, but only two bars 13 are visible in Figure 1. Each bar 13 is movable along its longitudinal axis as it passes through a through-hole 15 in the radiation shield 4, which is a leak-proof closure between the upper compartment 2 and the reactor compartment 3. The second end 20 of each bar 13 is shown engaged and locked with the reactor vessel lid shield 8 in the reactor compartment 3. Therefore, the lifting element is shown in the retracted position in Figure 1, with the reactor vessel lid shield 9 covering and sealing the reactor vessel 6 within the reactor compartment 3. Each bar 13 may be a threaded bar 17, which is lowered along its longitudinal axis by a drive mechanism 14, and the second end 20 (lower end) of the threaded bar 17 engages and fits with the threads 21 of the receiving structure of the lid shield 8, thereby engaging and locking with the lid shield 9 to the retracted position. Subsequently, the second end 20 of the bar lowers further into the threads 21 of the receiving structure, and the bar 13 is locked in the threads 21 of the receiving structure.

[0091] From the retracted position of the lifting mechanism shown in Figure 1, the reactor vessel lid assembly 7 is lifted vertically, thereby being projected by the lifting mechanism to a higher position within the reactor compartment 3 shown in Figure 2. The lifting of the reactor vessel lid assembly 7 is performed by engaging the first end 18 (upper end) of the threaded bar 17 with the drive mechanism 14, for example, by engaging the threads of the bar with the threads of the drive mechanism 14 and rotating the threads 19 contained in the drive mechanism 14 to move the bar 13 along its longitudinal axis.

[0092] The reactor vessel lid assembly 7, including the upper reactor plenum 10, is shown in a lifted position, in contact with the underside of the radiation shield 4. This allows the reactor vessel lid shield 8 to provide a seal between the upper compartment 2 and the reactor compartment 3. Furthermore, several bundles of control rods 32 are shown, connected via drive rods 33 to a control rod drive mechanism 34 installed within the upper compartment 2. Each of these bundles has several control rods 32, and each would ideally have its own drive rod 33 and control rod drive mechanism 34; however, only one such bundle or rod 32, and its associated drive rod 33 and drive mechanism 34, is illustrated. The control rod drive mechanism 34 is fixed to a separation section 35 of the radiation shield 4. This separation section 35 can be lifted together with the reactor vessel lid assembly 7 using a lifting element. A vertical spacer structure 36 is illustrated, which integrates the separation section 35 and the reactor vessel lid shield 8 into a single movable unit by connecting the separation section 35 to the reactor vessel lid shield 8. When the reactor vessel lid assembly 7 is lifted, the separation portion 35 moves accordingly, as it is connected to the lid assembly 7. The figure shows the separation portion 35 of the radiation shield in the lifted position and the reactor vessel lid shield 8, which forms a seal between the two compartments as described above.

[0093] Figure 2 also shows a gantry crane 26 having a graphite moderator structure 38 supported by a wire from a hoisted trolley (not shown), the trolley being supported by a transverse beam 7. In Figure 2, the reactor lid is lifted. The transverse beam 7 is positioned on two gantry crane rails 29, each fixed to walls 30, 31 facing each other, the rails 29 allowing the transverse beam 7 to slide and position itself appropriately for the gantry crane 26 to perform maintenance work inside the open reactor vessel 6.

[0094] Figure 3 shows the reactor structure 1 from Figure 2 as a cross-section along BB, and also shows the reactor structure 1 from the side. In Figure 3, the reactor lid is raised.

[0095] Figure 3 shows that a storage area 25 within the reactor compartment 3 is located behind the reactor vessel 6 and is capable of holding several spent graphite columns (not shown) or fuel tubes (not shown). A new, unused graphite column 38 is shown descending from the upper compartment 2 and entering the reactor compartment 3 through the reactor compartment hatch 24. Two of the four bars 17 are shown in Figure 3, one of which is also shown in Figure 1, while the other bar 17 is not shown in Figure 1.

[0096] Figure 4 shows a plan section of the reactor structure 1, showing the reactor vessel 6 with the vessel lid shield (not shown) removed and lifted above the illustrated portion to open it. Figure 2 shows a plan section CC with the reactor lid lifted. The graphite columns 38 of MSR5 have a hexagonal cross-section when viewed from above and are arranged in a regular pattern within the reactor vessel 6. The gantry crane 26 is shown stopped above the replaced graphite columns in a storage area 25 adjacent to the reactor vessel 6. The gantry crane 26 has two crossbeams 27 with a trolley with a hoist 28 between them.

[0097] Another reactor structure 1 of the present invention is shown in Figure 5 as a cross-sectional view along AA showing a front cross-section of the reactor structure 1. In Figure 5, the reactor lid is in a fixed position. Figure 5 shows the reactor structure 1 having an upper compartment 2 above the reactor compartment 3, with compartments 2 and 3 separated by a radiation shield 4. Two bars 13, which are part of a lifting element, are shown, each having a first end 18 that engages with a drive mechanism 14 installed on the floor of the radiation shield 4 in the upper compartment 2. Each of the bars 13 is movable along its longitudinal axis as it passes through a through-hole 15 in the radiation shield 4, the through-hole 15 being a leak-proof closure between the upper compartment 2 and the reactor compartment 3. The second end 20 of each bar 13 is shown engaged and locked with the reactor vessel lid shield 8 in the reactor compartment 3. Thus the lifting element is shown in the stowed position in Figure 5, and the lid shield 9 covers and seals the reactor vessel 6 in the reactor compartment 3. Each bar 13 may be a threaded bar 17, which is lowered along its longitudinal axis by a drive mechanism 14, and the second end 20 (lower end) of the threaded bar 17 engages and fits with the threads 21 of the receiving structure of the lid shield 8, thereby engaging and locking with the lid shield 9 to reach the stowed position. Subsequently, the second end 20 of the bar 17 is lowered further into the threads 21 of the receiving structure, and the bar 17 is locked in the threads 21 of the receiving structure.

[0098] From the retracted position of the lifting mechanism shown in Figure 5, the reactor vessel lid assembly 7 is lifted vertically, thereby being projected by the lifting mechanism to a higher position within the reactor compartment 3 shown in Figure 6. In Figure 6, the reactor lid is lifted. The lifting of the reactor vessel lid assembly 7 is performed by engaging the first end 18 (upper end) of the threaded bar 17 with the drive mechanism 14, for example, by engaging the threads of the bar 17 with the threads of the drive mechanism 14, and rotating the threads contained in the drive mechanism 14 to move the bar along its longitudinal axis.

[0099] The reactor vessel lid assembly 7, including the upper reactor plenum 10, is shown in a lifted position, in contact with the lower side of the radiation shield 4. This illustrated example of a reactor structure has control rods (not shown) that can be positioned in the reactor core by a drive mechanism that brings them into horizontal insertion from the side of the reactor vessel.

[0100] Figure 6 also shows a gantry crane 26 having a graphite moderator structure supported by a wire from a hoisted trolley (not shown), the trolley being supported by a transverse beam 27. The transverse beam 27 is positioned on two gantry crane rails 29, each fixed to walls 30, 31 facing each other, the rails 29 allowing the transverse beam 7 to slide and position itself appropriately for the gantry crane 26 to perform maintenance work inside the open reactor vessel 6.

[0101] Example 1 The graphite moderator structure may be replaced as shown in the following example.

[0102] After a predetermined operating period, the columnar graphite moderators, which have a hexagonal cross-section, need to be replaced. The reactor is shut down by inserting control rods into the core from the side to stop the fission reaction and cease the circulation of fuel salts. The fuel salts are discharged into a drain tank located below the core, and the exhaust gas system in the upper plenum is shut down. Each of the three bars, all of which are threaded bars, is moved along its respective longitudinal axis by its respective drive mechanism located in the upper compartment of the reactor structure. For each of the threaded bars, the lower end of the threaded bar is inserted into the corresponding threads of the receiving structure of the reactor vessel lid shield, and the threaded bar is locked into the threads of the receiving structure as it rotates into the threads. The threaded bars then move synchronously upward along their longitudinal axes to perform the lifting operation of the reactor vessel lid assembly, which comprises the reactor vessel lid shield, the reactor vessel lid, and the integrated unit of the upper plenum. The reactor vessel lid assembly is moved upward so that the upper side of the reactor vessel lid shield contacts the lower surface of the radiation shield, and the radiation shield separates the upper section from the reactor section.

[0103] Subsequently, after a period of time has passed allowing radiation levels to decrease, the gantry crane is assembled. The first reactor compartment hatch is opened by a motor drive from the upper compartment, and a trolley with a hoist is lowered through the open hatch until it reaches two spaced crossbeams, at which point the trolley with the hoist is positioned and connected to the upper side of the two crossbeams. The crossbeam drive unit (bridge drive unit) is lowered through the second open reactor compartment hatch and positioned and connected to the crossbeams, and this position is guided using a camera that was lowered into the reactor compartment through the first open reactor compartment hatch.

[0104] After the hoist-equipped trolley and crossbeam drive unit are positioned, a gantry crane is positioned above, and a single graphite column is grasped from above by a gripper. The graphite column is then lifted by the hoist and translated using the bridge drive unit, thereby positioning the trolley above the storage area at this point. The graphite column is then lowered into the available space for storage and released.

[0105] The new, unused graphite column is lowered through a second, open hatch, positioned so that a gripper can grasp the top end of the column, and a gantry crane positions the unused graphite column in the available space within the reactor. In all methods of replacing graphite columns, the removal of all spent graphite columns to be replaced is carried out before the unused graphite columns are introduced and inserted into the reactor core.

[0106] Example 2 A power barge has two reactor structures side-by-side in the middle of the barge. The two reactor structures are separated from each other and can be operated independently, but they share a side wall that divides them. They also share a radiation shield that separates the upper section of each reactor structure from the reactor section. The radiation shield also forms part of the barge's bulkhead.

[0107] This power barge generates electricity and supplies it to onshore facilities via cables. The barge houses equipment for power supply, such as steam turbine generators and heat exchangers that utilize heat from the reactor. Other onboard equipment is a storage area within the reactor structure, sealed by radiation shielding and further shielding surrounding the reactor vessel. The storage area can hold the graphite moderator structure, graphite lining, fuel pipes, radiation-exposed maintenance equipment, and other high- and low-level waste for the entire barge life until decommissioning.

Claims

1. The reactor structure (1) includes an upper section (2) above the reactor section (3), and the reactor section is separated from the upper section by a radiation shield (4). A molten salt reactor (MSR) (5) is located within the reactor compartment (3), and the MSR (5) is - Reactor vessel lid shield (8) and reactor vessel lid (9) The reactor vessel (6) comprises a reactor vessel lid assembly (7) having a reactor vessel lid assembly (7) equipped with The lifting element (12) is located within the reactor structure (1), and the lifting element (12) is - At least one bar (13) that is substantially vertical and axially adjustable along the longitudinal axis by a drive mechanism (14) located within the upper section (2) Equipped with, A reactor structure (1) having at least one through-hole (15) for at least one bar (13) provided in the radiation shield (4), and the reactor vessel lid shield (8) having at least one receiving structure (16) configured to engage and lock with the at least one bar (13).

2. The reactor structure (1) according to claim 1, wherein the bar (13) is a threaded bar (17), the first end (18) of the threaded bar (17) is capable of engaging with the threads (19) of the drive mechanism in the upper compartment (2), and the second end (20) of the threaded bar (17) is capable of engaging and locking the threaded bar (17) with the threads (21) of the receiving structure of the reactor vessel lid shield (8).

3. The reactor structure (1) according to claim 1, wherein the lifting element (12) is selected from the group consisting of a rack and pinion, a lifting jack, a ram / piston, a telescoping linear actuator, and a rigid chain actuator.

4. The reactor structure (1) according to claim 3, wherein the bar (13) is equipped with a foldable forklift.

5. The reactor structure (1) according to any one of the above claims, further comprising an airlock (22) within the upper compartment (2), wherein the airlock (22) comprises an upper compartment hatch (23) for separating the upper compartment (2) from the external environment and at least one reactor compartment hatch (24) for separating the upper compartment (2) from the reactor compartment (3).

6. The reactor structure (1) according to any one of the above claims, further comprising within the reactor compartment (3) a storage area (25) for spent graphite moderator, spent graphite shield, and spent fuel tubes.

7. Within the aforementioned reactor compartment (3), A reactor structure (1) according to any one of the above claims, further comprising at least one transverse beam (27), a transverse beam drive unit, and a trolley with a hoist (28), wherein the transverse beam (27) extends from a first wall (30) of the reactor compartment (3) to a second wall (31) of the reactor compartment (3) opposite the first wall (30), and a gantry crane (26) on which the at least one transverse beam (27) is attached to gantry crane rails (29) on the first wall (30) and the second wall (31).

8. The reactor structure (1) according to any one of the above claims, wherein the reactor vessel lid assembly (7) comprises a reactivity control means (11), the reactivity control (11) means comprising at least one control rod (32), the at least one control rod (32) being axially adjustable along the longitudinal axis of the at least one control rod (32), and connected via at least one drive rod (33) to a control rod drive mechanism (34) located in the upper compartment (2), the mechanism (34) being fixed to a separation portion (35) of the radiation shield (4), the portion (35) being fixed to the upper side of the reactor vessel lid shield (8) by a vertical spacer structure (36).

9. The reactor vessel lid assembly (7) - The reactor vessel lid shield (8), - The reactor vessel lid (9), - Upper reactor plenum (10), and - The reactivity control means (11), A reactor structure (1) according to any one of the above claims, comprising an integrated unit.

10. The reactor structure (1) according to claim 9, wherein the integrated unit is a mechanically integrated unit.

11. The reactor structure (1) according to any one of the above claims, wherein the reactor structure (1) is sealed from the external environment.

12. A reactor structure (1) according to any one of the above claims, comprising a drain tank (37) for storing molten salt.

13. A power barge comprising at least one reactor structure (1) according to any one of claims 1 to 12 for generating heat produced by a nuclear fission reaction, and at least one steam turbine generator for generating electricity using the generated heat.

14. A method for performing maintenance work in a reactor compartment (3) according to any one of claims 1 to 12: The steps include: engaging and locking at least one bar (13) with the reactor vessel lid shield (8), and engaging the drive mechanism (14) of the bar (13) to lift the reactor vessel lid shield (8) and open the reactor vessel (6) from above; The steps include: positioning at least one hoisted trolley (28) on at least one transverse beam (27), and positioning at least one transverse beam drive unit on at least one transverse beam (27), wherein the at least one hoisted trolley (28), the transverse beam drive unit, and the at least one transverse beam (27) are included in a gantry crane (26), the at least one transverse beam (27) extend from a first wall (30) of the reactor compartment (3) to a second wall (31) of the reactor compartment (3) opposite the first wall (30), the at least one transverse beam (27) is attached to gantry crane rails (29) on the first wall (30) and the second wall (31), and the arrangement is, The steps include: opening a reactor compartment hatch (24) that separates the upper compartment (2) from the reactor compartment (3); lowering at least one hoisted trolley (28) and at least one crossbeam drive unit from the upper compartment (2) through the opened reactor compartment hatch (24); and connecting the at least one hoisted trolley (28) and the at least one crossbeam drive unit to the at least one crossbeam (27); The steps include: positioning at least one hoisted trolley (28) above the area to be maintained; The steps include performing maintenance by lowering maintenance equipment to the vicinity of the work area to be maintained, A method that includes this.

15. The method according to claim 14, wherein the MSR (5) comprises at least one graphite moderator structure (38), and the maintenance work is the replacement of the at least one graphite moderator structure (38) in the MSR (5).

16. The method according to claim 14 or 15, wherein the MSR (5) comprises at least one fuel salt pipe (39).

17. The method according to claim 16, wherein the at least one fuel salt pipe (39) is made of graphite, and the maintenance work is the replacement of the at least one fuel salt pipe (39).

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