Fuel assembly handling system and method

Abstract

A fuel assembly handling system for moving fuel assemblies (20) between a reactor room (1) and a storage room (2), comprising a carousel installed in a transfer chamber (3), the transfer chamber (3) communicating with the reactor room (1) via a reactor well (32), with a first storage room (2a) via a first storage well (34), and with a second storage room (2b) via a second storage well (36), the carousel (30) comprising a plurality of housings (40), each housing (40) configured to accommodate a fuel assembly (20), the carousel (30) configured to move the housings (40) within the transfer chamber (3) between a reactor position (42) opposite the reactor well (32), a second position (44) opposite the first storage well (34), and a third position (46) opposite the second storage well (36).

Description

Technical Field

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[0001] [Cross - reference to Related Applications] This patent application claims the priority of Italian Patent Application No. 102023000017415 filed on August 21, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] The present invention relates to the field of nuclear energy, particularly to the handling of fuel assemblies. More specifically, the present invention relates to a fuel assembly system and method for moving a fuel assembly between a reactor chamber configured to house a nuclear reactor and a storage chamber configured to store the fuel assembly.

Background Art

[0003] The core of a nuclear reactor is usually composed of a fuel assembly that groups together bundles of coated rods or pins enclosing pellet - shaped fissile material or fertile material.

[0004] During the operation of a nuclear reactor, since the nuclear fuel contained in the fuel assembly is depleted, it needs to be replaced regularly. Since the depletion of the fuel assembly depends on its position within the core, not all fuel assemblies are irradiated simultaneously. Fuel assemblies that are not completely depleted are usually moved into the core.

[0005] Assemblies are usually designed to remain in the core for 2 to 5 years. The replacement of irradiated fuel with new fuel is carried out by periodically (e.g., every 6 to 24 months) refilling a part (20 - 50% of the total number of assemblies) of the core, depending on the type of operation and the performance level of the assemblies. Therefore, the assembly includes, at its upper end, a gripping head that can lift and move the assembly. During this operation, it is necessary to switch off the nuclear reactor.

[0006] New fuel assemblies are typically manufactured in pellet manufacturing plants. They then must be transported to nuclear power plants, where they are placed in storage facilities before being transferred to the reactors.

[0007] Instead, irradiated fuel assemblies that require replacement are removed from the reactor and placed in a dedicated storage facility before being transported to a dismantling / recycling site.

[0008] The replacement period for these fuel assemblies is a significant cost factor because the reactor is shut down during this period. Therefore, the present invention aims to shorten the time required for their replacement.

[0009] The loading and unloading of these fuel assemblies is typically carried out by an assembly elevator system or articulated or open vessel handling (e.g., pressurized water reactors: PWRs) or by closed vessel handling with a rotating cap system (e.g., fast neutron reactors: FNRs).

[0010] The systems for handling fast neutron reactor assemblies, particularly liquid metal-cooled reactors, are more complex than those for water reactors. In fact, in the latter case, it is possible to open the container and operate it visually, utilizing the neutron shielding of several meters of water available to reposition the reactor core.

[0011] Various systems have been developed to limit the reactor shutdown time required when replacing fuel assemblies.

[0012] As an example, Patent Document 1 can be cited. This describes a fuel assembly loading / unloading device that can pass fuel assemblies between a primary loading / unloading ramp communicating with the reactor vessel and a secondary loading / unloading ramp communicating with the storage or loading area of ​​the assemblies. Handling of the fuel assemblies consists of transferring the irradiated fuel assemblies to a handling container using a first handling device equipped with a handling arm. A second step following the first step is to transport the handling container containing the irradiated fuel assemblies from the second handling device upwards to the outside of the reactor vessel above the shielding plate. Thereafter, the irradiated fuel assemblies removed from the reactor vessel are transported to an external storage container by a handling system such as a handling hood.

[0013] Patent Document 2 describes a device for moving fuel assemblies by transferring them from the reactor core to a storage carousel adjacent to the core. The fuel loading machine is mounted across an inner rotating cap. Each loading machine is equipped with a grappling hook and means for moving vertically upward or downward or laterally via a corresponding tubular guide. Thus, a fuel assembly can be removed from the reactor core by aligning one of the loading machines over the core, lowering the grappling hook of this loading machine to dock the fuel assembly, then lifting the grappling hook to detach the fuel assembly from the core and lifting it into the corresponding guide. Near the transfer machine, the fuel assembly storage carousel is equipped with a rotor with a series of fuel assembly holders around it. A drive shaft can rotate the rotor by a motor. The fuel assemblies can then be stored in the reactor or completely removed from it by rotating the storage carousel to move the fuel assemblies vertically below the guide tubes and discharge passages, and by removing the fuel assemblies through these tubes using another means equipped with grappling hooks. The fuel assemblies are then introduced into the reactor core by reversing these operations.

[0014] Finally, Patent Document 3 proposes a device comprising at least one rotating drum containing at least two concentric storage areas (a storage area for new fuel assemblies and a storage area for irradiated fuel assemblies). This device is placed inside a container, thereby allowing the assemblies to be "cooled," i.e., their residual energy to be reduced, and thus allowing them to be discharged from the reactor, and conversely, allowing new fuel to be reintroduced into the reactor. While irradiated fuel assemblies are being replaced with the reactor shut down, the rotating drum is positioned at the height of the pantograph arm to receive the irradiated fuel assemblies, and then rotates to make the new fuel assemblies available. Thus, the rotation of the pantograph arm is limited to a minimum. This operation can be repeated as many times as needed.

[0015] Current systems are unable to effectively handle small modular reactor fuel assemblies (SMRs) that use liquid metal as a heat transfer medium. This is because SMRs are too large and require extensive maintenance. Therefore, developing an effective handling system by limiting the volume of the reactor vessel would be a significant advantage. [Prior art documents] [Patent Documents]

[0016] [Patent Document 1] French Patent No. 2486297 [Patent Document 2] French Patent No. 2158491 Specification [Patent Document 3] French Patent No. 2953319 Specification [Patent Document 4] Japanese Patent Application Publication No. 63-063996 [Patent Document 5] U.S. Patent No. 4167442 [Overview of the Initiative] [Problems that the invention aims to solve]

[0017] The object of the present invention is a system and method for handling fuel assemblies of a nuclear reactor, particularly a fast neutron reactor, using a transfer carousel that facilitates the transfer of fuel assemblies between the reactor and a storage area. This system allows for parallel operation at multiple stations, leading to time savings and thus limiting reactor downtime. .

[0018] Accordingly, the present invention aims to propose a fuel assembly handling system that makes loading and unloading fuel assemblies easier and faster, and in particular a fuel assembly handling system that enables loading of new fuel into a first storage area and removal of irradiated fuel assemblies into a second storage area, while ensuring a high level of safety by performing unloading or loading simultaneously through a reactor well that opens into the reactor chamber. [Means for solving the problem]

[0019] To that end, the present invention proposes a fuel assembly handling system for moving fuel assemblies between a reactor chamber configured to house a reactor and a storage chamber configured to store fuel assemblies, wherein the handling system includes a carousel installed in a transfer chamber, the transfer chamber communicating with the reactor chamber via a reactor well, with a first storage chamber via a first storage well, and with a second storage chamber via a second storage well, the carousel includes (a plurality of) housings, each housing configured to house a fuel assembly, and the carousel is configured to move the housings within the transfer chamber between a reactor position facing the reactor well, a second position facing the first storage well, and a third position facing the second storage well.

[0020] The present invention is advantageously complemented by the following distinct features, either individually or in various possible combinations thereof: - The reactor well extends between the plate of the reactor chamber and the upper part of the transfer chamber, and each storage well extends between the storage chamber and the upper part of the transfer chamber; - The carousel includes a shaft configured such that the housing rotates, and the housing is dispersedly arranged around the shaft according to an angular offset in the rotation plane, and the reactor and the storage wells are evenly dispersedly arranged around the shaft with the same angular offset; - The carousel includes a housing support displaceable along the shaft to accommodate the housing and change the height of the housing in the transfer chamber; - The system includes (a plurality of) cases configured to be received within the housing of the carousel, each case being configured to accommodate a fuel assembly and including a removable plug configured to seal the case when a fuel assembly is present within the case. - The system can be equipped with a suitable heating device suitable for heating the cases. - The system includes a handling hood movable within the reactor chamber and configured to dock with the reactor well, the handling hood extending through the reactor well and including gripping members adapted to grip and lift the plug of the case or the fuel element depending on the situation; - The system includes a movable member configured to selectively position itself within the reactor well under the handling hood when the handling hood is fixed to the well, the movable member being configured to receive the plug of the case; - The reactor well includes two slide valves configured to selectively seal the reactor well, and the movable member is disposed between the two slide valves.

[0021] The present invention also relates to a nuclear power plant comprising a reactor chamber housing a reactor and at least two storage areas for storing fuel assemblies, and comprising a fuel assembly handling system according to the present invention.

[0022] The present invention also relates to a method for handling fuel assemblies between a reactor chamber configured to house a reactor and two storage chambers configured to store fuel assemblies, using a fuel assembly handling system according to the present invention, and includes the following steps: a) A step of loading a fuel assembly, sealed within its housing by a cap, into the housing of the carousel at a second position via a first storage well, b) A step of moving the housing from the second position to the reactor position opposite the reactor well by rotating the carousel, c) The plug of the case surrounding the fuel element is removed inside the reactor well. d) The step of removing the fuel assembly from the housing through the reactor well to the reactor location, e) The step of loading another fuel assembly into the housing at the reactor location via the reactor well, f) A step of moving the housing from the reactor position to a third position opposite the second storage well by rotating the carousel, g) The step of removing the other fuel assembly from the housing at a third position via a second storage well, h) The step of moving the housing from a third position to a second position opposite the first storage well by rotating the carousel.

[0023] Preferably, between two consecutive displacements of the housing by the carousel, the fuel assembly is removed from the housing at the reactor position, loaded into the housing positioned at the reactor position, loaded into the housing at a second position, and removed from the housing at a third position. Furthermore, it is preferable that the case housed within the housing contains an inert atmosphere with at least a plug closing the case and the fuel assembly housed within the case.

[0024] Furthermore, the present invention relates to a method for handling fuel assemblies in combination with or independently of a transfer carousel, the method comprising: - The case inside the transfer chamber is docked to the well connecting the transfer chamber to the reactor chamber containing the reactor, and the case is closed by a plug. - The gripping member of the handling hood docked to the reactor well in the reactor room enters the reactor well and grips the plug. - The movable element is located in the reactor well under the handling hood and accepts the plug. - The movable elements are retracted, clearing the passage to the reactor well. - The fuel assemblies pass through the reactor well, are removed from the casing, or placed back into the casing.

[0025] This method can include the following steps: - The step of positioning the movable element that supports the plug in the reactor well under the handling hood, - The step of inserting the gripping member into the reactor well and gripping the plug, - A step in which the movable element is retracted to clear a passage within the reactor well. - The step of inserting the gripping member into the reactor well, replacing the plug, and closing the case. [Brief explanation of the drawing]

[0026] [Figure 1] This figure schematically shows a cross-section of an assembly comprising a reactor chamber for housing a nuclear reactor, a storage area, and a transfer device installed in a transfer chamber, according to a possible embodiment of the present invention. [Figure 2] This is a schematic top view showing an example of the arrangement of a transfer device between the reactor chamber and two storage areas according to a possible embodiment of the present invention. [Figure 3] This is a schematic top view showing an example of the arrangement of two transfer devices between three storage areas and four reactor chambers according to a possible embodiment of the present invention. [Figure 4] This diagram schematically shows a cross-section of the housing of the transfer device located on the opposite side of the reactor well to which the handling hood is docked. [Figure 5]This figure shows the steps of the method according to the present invention. [Figure 6a] This figure shows the configuration of a reactor well with empty cases installed during the initial step of loading irradiated fuel assemblies into their cases. [Figure 6b] This figure shows the step of loading the irradiated fuel assemblies into the case, following the step shown in Figure 6a. [Figure 6c] This figure shows the step of loading the irradiated fuel assemblies into the case, following the step shown in Figure 6b. [Figure 6d] This figure shows the step of loading the irradiated fuel assemblies into the case, following the step shown in Figure 6c. [Figure 6e] This figure shows the step of loading the first irradiated fuel assembly into the case, following the step shown in Figure 6d. [Figure 6f] This figure shows the step of loading the irradiated fuel assemblies into the case, following the step shown in Figure 6e. [Figure 6g] This figure shows the step of loading the irradiated fuel assemblies into the case, following the step shown in Figure 6f. [Figure 6h] This figure shows the step of loading the irradiated fuel assemblies into the case, following the step shown in Figure 6g. [Figure 7a] This diagram shows the steps involved in removing a new fuel assembly from its case. [Figure 7b] This figure shows the step of removing a new fuel assembly from the case, following the step shown in Figure 7a. [Figure 7c] This figure shows the step of removing the new fuel assembly from the case, following the step shown in Figure 7b. [Figure 7d] This figure shows the step of removing the new fuel assembly from the case, following the step shown in Figure 7c. [Modes for carrying out the invention]

[0027] Further features, objectives, and advantages of the present invention will become apparent from the following description.

[0028] The drawings are provided as non-limiting embodiments of the present invention. They constitute a schematic representation of the principles intended to facilitate understanding of the present invention and are not necessarily based on the scale of actual application. In particular, the relative dimensions of the various elements constituting the reactor do not reflect reality.

[0029] A fuel assembly is a collection of elements composed of nuclear fuel, particularly fissile material, generally having an elongated shape along its longitudinal axis, and containing multiple fuel rods or needles. Each fuel rod or needle (150-300 per group) is sheath-shaped, and within it, columns of fissile material (e.g., MOX) pellets are stacked, and a nuclear reaction that releases heat takes place. These assemblies generally have a hexagonal cross-section with sides of several tens of centimeters and a length of several meters.

[0030] Fuel assemblies can be new or irradiated. New fuel assemblies contain enough fissile material to sustain nuclear reactions in the reactor, while irradiated fuel assemblies are irradiated to a degree that makes them unusable in a reactor unless properly treated. In other words, an "irradiated fuel assembly" is an assembly that contains potentially usable fissile material, but the neutron emissivity of the fuel rod sheath containing the fissile material and the internal fission gas pressure have reached the maximum permissible values ​​that would cause the sheath to crack, resulting in the release of fissile material and fission gases. Fuel assemblies may also be dummy fuel assemblies or false fuel assemblies that do not contain fissile material.

[0031] To gain a good understanding of the present invention, various embodiments of a fuel assembly handling system will be described as non-limiting examples with reference to the accompanying drawings. Figure 1 is a cross-sectional view of a nuclear power plant comprising a reactor chamber containing a reactor, a storage area, and a transfer device installed in a transfer chamber.

[0032] In the illustrated example, the reactor is non-limited to a fast neutron reactor (FNR), but the present invention is applicable to other types of reactors. For example, an FNR can accommodate 30 to 600 fuel assemblies. Each fuel assembly needs to be replaced approximately every 2 to 4 years, which results in the reactor being shut down for several days.

[0033] The reactor 10 includes a main vessel 12 having a vertical axis suspended on a horizontal plate 14. The main vessel 12 is filled with a liquid-cooled metal, such as lead. Above the liquid metal level is a layer of inert gas, usually argon. The horizontal plate 14 rests on a concrete floor 15. The reactor chamber 1, which houses the reactor 10, is separated by a containment cell 16, typically made of concrete, of which the floor 15 is part. The reactor chamber 1 integrates the containment space of the reactor 10 and the fuel assembly handling equipment. The reactor core 18 of the reactor 10 is located inside an additional vessel or inner vessel 19 that separates two distinct regions within the main vessel 12, is immersed in liquid metal, and is essentially composed of fuel assemblies 20.

[0034] A nuclear power plant also includes at least two storage chambers 2 configured for storing fuel assemblies. In particular, new fuel assemblies can be stored using at least a first storage chamber 2a, and irradiated fuel assemblies can be stored using at least a second storage chamber 2b. For safety reasons, the storage chambers 2 are separated from the reactor chamber 1 and do not communicate with it. In particular, the containment cell 16 defining the reactor chamber 1 can partially partition the storage chambers 2. Preferably, the storage chambers 2 are adjacent to and continuous with the reactor chamber 1.

[0035] The nuclear power plant also includes a transfer chamber 3 that houses a transfer carousel 30, or rotary transfer device 30. This transfer chamber 3 communicates with the reactor room 1 via a reactor well 32, with the first storage chamber 2a via a supply well 34, and with the second storage chamber 2b via a discharge well 36. The reactor well 32 is responsible for transferring fuel assemblies between the reactor room 1 and the transfer chamber 3, the supply well 34 is responsible for transferring fuel assemblies, usually new fuel assemblies, from the first storage chamber 2a to the transfer chamber 3, and the discharge well 36 is responsible for transferring fuel assemblies, usually irradiated fuel assemblies, from the transfer chamber 3 to the second storage chamber 2b.

[0036] The transfer chamber 3 is separated by a chamber 37 and has a substantially cylindrical shape, for example, around a vertical axis. The upper part 38 of the transfer chamber 3 is surrounded by a material structure that absorbs any radiation that may be emitted and forms the upper part of the cell 37. Wells 32, 34, and 36 traverse the upper part 38 of the transfer chamber 3. It is preferable that the wells 32, 34, and 36 can be sealed with removable lids. Each lid is provided with a system that allows it to move by known means between a sealed position that closes the wells 32, 34, and 36 and a standby position that leaves the wells 32, 34, and 36 open. For example, VAT valves (V1, V2, V4) can be used, preferably electrically operated. The wells 32, 34, and 36 are evenly distributed according to rotational symmetry around the vertical axis.

[0037] The transfer chamber 3 houses a carousel 30 containing housings 40, each housing 40 configured to contain a fuel assembly 20, and the carousel 30 is configured to move the housings 40 within the transfer chamber 3 by rotation. More precisely, the carousel 30 moves each housing 40 between positions 42, 44, and 46 facing wells 32, 34, and 36, respectively. Typically, the carousel 30 contains three housings 40. The carousel 30 rotates following the successive loading / unloading positions of the fuel assemblies 20, with each housing 40 sequentially aligning with the loading / unloading wells 32, 34, and 36 located within the transfer chamber cell 3. The carousel 30 is preferably made of radiation-resistant steel.

[0038] The carousel 30 includes a shaft 47 configured to rotate the housings 40, which are evenly distributed around the shaft 47 with an angular offset in a rotational plane that is preferably horizontal. The reactor wells 32 and storage wells 34, 36 are evenly distributed around the shaft 47 with the same angular offset. This angular offset is preferably 120° if the carousel includes three housings 40.

[0039] In the example shown in Figure 2, the transfer chamber 3 ensures the movement of fuel assemblies 20 between a single reactor chamber 1, a first storage chamber 2a for storing new fuel assemblies 20, and a second storage chamber 2b for storing irradiated fuel assemblies 20. In this case, each reactor chamber 1 between the first storage chamber 2a and the second storage chamber 2b can only have one well 32, 34, or 36.

[0040] However, the transfer chamber 3 may comprise several sets of three angularly offset wells 32, 34, and 36. However, it is possible for one identical fuel assembly handling system 20 to supply several reactors 10, or for one identical storage chamber 2 to have several carousels 30. In the example of Figure 3, a first carousel 30a housed within a first transfer chamber 3a supplies two reactor chambers 1a and 1b, each housing two reactors 10a and 10b. The first transfer chamber 3a is provided with reactor wells 32a and 32a' that communicate with each of the two reactor chambers 1a and 1b. The two supply wells 34 connect the first transfer chamber 3a to the first storage chamber 2a': the first supply well 34a has a typical 120° angular offset from the first reactor well 32a around the carousel 30a, and the second supply well 34a' has the same angular offset as the second reactor well 32a', typically 120°. Similarly, the two discharge wells 36 connect the first transfer chamber 3a to the second storage chamber 2b: the first discharge well 36a has a typical 120° angular offset from the first reactor well 32a around the carousel 30a, and the second discharge well 36a' has the same angular offset as the second reactor well 32a', typically 120°.

[0041] Similarly, the second carousel 30b is housed in a second transfer chamber 3b that supplies two reactor chambers 1c and 1d, each containing one of the two reactors 10c and 10d. Reactor wells 32b and 32b' are provided to connect the second transfer chamber 3b with the two reactor chambers 1c and 1d. The two supply wells 34 connect the second transfer chamber 3b to another first storage chamber 2a''; that is, the first supply well 34b has a typical 120° angular offset from the first reactor well 32b around the carousel 30b, and the second supply well 34b' has the same angular offset as the second reactor well 32b', typically 120°. Similarly, the two discharge wells 36 connect the second transfer chamber 3b to the second storage chamber 2b. The first discharge well 36b has a typical 120° angular offset from the first reactor well 32b around the carousel 30b, and the second discharge well 36b' has the same angular offset as the second reactor well 32b', typically 120°.

[0042] Therefore, in the example of Figure 3, there are two transfer chambers 3a, 3b with the same storage chamber 2b, transfer chambers 3a, 3b shared by two reactor chambers 1a, 1b, 1c, 1d, or storage chambers 2a, 2a' shared by two reactors 10a, 10b, 10c, 10d via a single transfer chamber 3a, 3b. Thus, the possibilities are diverse and not limited to this particular example. The arrangement of the series of wells 32, 34, 36 is selected so that reactor chamber 1 can be associated with two storage chambers 2a, 2b to enable the handling of fuel assemblies 20.

[0043] The current trend in the construction of nuclear reactors 10 is to group these reactors 10 into, for example, two or four units at the same site in order to reduce some investment by pooling specific components of these reactors 10. Using the same fuel assembly handling system 20 for several reactors 10 not only reduces the cost of constructing the grouped reactors 10 at the same site, but also allows for more frequent maintenance of the mechanical elements of the handling system in any of the reactors 10 located in close proximity to each other. For a single reactor 10, the handling system is activated at intervals that are significantly spaced out over time, resulting in very long downtimes that are detrimental to this handling system. Sharing the fuel assembly handling system 20 allows for more frequent use and therefore less downtime.

[0044] As shown in Figures 1 and 4, the carousel 30 comprises a housing support 31 that houses the housing 40, the housing support 31 comprising, for example, a disk or an arm extending from the shaft 47 and rotatably mounted on the shaft 47. The housing support 31 preferably extends over the carousel 30 and into the transfer chamber 3, and preferably is movable along the shaft 47 to change the height of the housing 40 within the transfer chamber 3.

[0045] Preferably, the shaft 47 extends from the upper 38 of the transfer chamber 3 at the lower 39 opposite the upper 38 and is rotatably mounted on the upper 38 and lower 39. A motor is incorporated into the shaft 47, for example, at its upper 70' or lower 70, to rotationally drive the carousel 30.

[0046] Each housing 40 is shaped to receive a case 50, which can be installed in the housing 40 by parallel movement downward in the vertical direction and removed from the housing by movement upward in the vertical direction. In particular, the housing may include a tubular body 52 that can accommodate a fuel assembly 20. The housing 40 typically has a through orifice 48 configured through which the body 52 of the case passes vertically, and a support means 49 for the case 50, such as a shoulder on which a portion of the case 50 rests. The inner diameter of the through orifice 48 of the housing 40 is larger than the diagonal of the cross-section of the case 50 so that the case 50 can be introduced vertically into the housing 40.

[0047] The support means 49 may be active and may include a gripper configured to clamp the case 50 and hold it in a predetermined position, preventing its vertical translation, and allowing the case 50 to freely translate vertically within the through orifice 48 in the released position. The support means 49 is preferably positioned above the through orifice 48.

[0048] Each housing 40 may include means for transmitting power to the case, and may include, for example, an electrical contactor configured to be electrically connected to the case 50 when placed inside the housing 40. The case 50 can then be powered by electricity from the housing 40 to power a heating device, for example, which is configured to heat the body 52 of the case 50.

[0049] Preheating of the fuel assemblies 20 before their introduction into the core can also be performed, for example, by a fixing system located below the well 34 and fixed to the wall of the chamber 3. This system may include an electrically heated gripper mechanism that can be mounted on the case 50 if necessary. This heating device is particularly advantageous for avoiding any thermal shock.

[0050] The cases 50 are configured to be received within the housing 40 of the carousel 30, and each case 50 is configured to house a fuel assembly 20 and includes a removable plug 54 configured to seal the case 50, particularly when the fuel assembly 20 is present inside the case 50. The plug 54 includes a circular portion having a diameter larger than the inner diameter of the circular portion of the body 52 of the case 50 and is configured to seal the case 50. For example, the plug 54 may include, for example, a circular projection formed to fit into a receiving space such as a groove located in the wall thickness of the body 52 of the case 50. Preferably, the plug 54 takes the shape of a cavity or recess, for example as shown, and typically includes a gripping area 56 located in the center of the plug 54, but may be any element that allows gripping by a gripping member 62, such as a projection that is gripped by a gripper in the shape of a mushroom, buckle, or handle, or that allows engagement of a gripping member 62.

[0051] The plug 54 is typically made of stainless steel and can be maintained, for example, by welding it to a metal gasket that is coated with a liquid and then cooled. For example, the body 52 of the case 50 has a groove at its upper end filled with molten metal, typically lead, into which a portion of the plug 54 is introduced when the plug 54 closes the case 50. If the lead is solid, the plug 54 is sealed in the case 50. Once the lead is liquefied, the plug 54 can be freely removed or introduced. To selectively liquefy the lead and selectively seal or loosen the plug 54, a heating element can be provided around the groove, for example, integrated in a holder 49 of the reactor well 32 or housings 42, 44 and 46, and powered by a support 31. Preferably, the case 50 housed in the housing 40 contains at least an inert atmosphere when the plug 54 closes the case 50 and the case 50 houses the fuel assembly.

[0052] As described above, each case 50 may be equipped with a heating device that heats the body 52 of the case 50. Typically, this heating device may include a conductive element that extends around the body 52, for example by wrapping itself around it, and is adapted to heat the case by the ohm effect or electrical induction.

[0053] Each case 50 is designed to accommodate a fuel assembly 20 and is therefore suitable for housing the fuel assembly 20 within its internal volume. The fuel assembly 20 comprises a body 22 extending in the longitudinal direction, and at the end of the body 22 is a handling head 23 that can grip and move the fuel assembly 20. As described above, the fuel assemblies 20 in the core 18 of the reactor 10 must be replaced periodically. The handling hood 60 is used to handle the fuel assembly 20 within the reactor chamber 1.

[0054] The handling hood 60 is vertically movable and can move horizontally, for example, along a bridge with a rolling track. The handling hood 60 includes a gripping member 62, such as a grappling hook or gripper, configured to grip the fuel assembly 20, lift it, move it by horizontal movement, and lower it again. The handling hood 60 is configured to house the fuel assembly 20 within an internal volume 63, which has a lower opening that is closed, for example, by a shutter. Preferably, a waterproof valve closes the lower opening of the internal volume 63. The handling hood 60 is preferably constructed integrally and airtightly to dock with the reactor 10 and the reactor well 32. Simultaneously with the fuel assembly 20, the internal volume 63 houses the gripping member 62 at its top.

[0055] The handling hood 60 includes a solid body (biological shield) made of armoring material to block nuclear radiation, and within it is an internal volume 63 for the fuel assembly 20. The fuel assembly 20 for a fast neutron reactor has considerable length relative to its lateral dimension. Therefore, in this case, the body of the handling hood 60 can have an elongated shape, and the housing of the fuel assembly 20 is preferably located within the internal volume 63 substantially axially at its central position.

[0056] To remove the fuel assembly 20 from the reactor core 18 of the reactor 10, the handling hood 60 can be moved above the fuel assembly 20 within the inner vessel 19. The horizontal plate 14 has a circular opening into which two sets of rotatable covers are fitted: a central rotatable large cover 64 and a rotatable small cover 66, which are offset from each other. The large cover 64 covers the upper opening of the inner vessel 19 and rotates around an axis located in the center of the large cover 64, while the small cover 66 covers the opening of the large cover 64 and rotates around its axis, but the latter is offset from the axis of the large cover 64. Thus, by rotating the large cover 64 and the small cover 66, a sealable access provided in the small cover 66 can be moved to the surface of the inner vessel 19, allowing access to different positions of the fuel assembly 20 within the inner vessel 19.

[0057] When access becomes resealable on the opposite side of the fuel assembly 20 for removal, the handling hood 60 can descend and dock with the resealable access (66') located within the small cover 66. The gripping member 62 of the handling hood 60 is movable vertically relative to the rest of the handling hood and descends until it reaches the handling head 23. The gripping member 62 of the hood then grips the handling head 23 and rises to carry the fuel assembly into the handling hood 60. The lifting mechanism of the overhead crane lifts the handling hood 60 away from the small cover 66. The shutter can be closed to securely house the fuel assembly 20 within the handling hood 60.

[0058] In the case of fuel assembly transfer, which will be described in detail below with reference to Figures 5, 6a-6h and 7a-7d, the overhead crane can move the handling hood 60 above the reactor well 32 and position the fuel assembly 20 within the well 50 of the housing 40 of the carousel 30.

[0059] The fuel assembly handling system allows the fuel assembly 20 to be moved between the reactor room 1 and the storage room 2, enabling simultaneous operations to be performed in parallel and saving considerable time.

[0060] The carousel 30 rotates between a reactor position 42 opposite the reactor well 32, a supply position 44 opposite the supply well 34, and a discharge position 46 opposite the discharge well 36, in the position where the housing 40 is positioned in the transfer chamber 3. Thus, the housing 40 is always facing the reactor well 32, the supply well 34, and the discharge well 36. Consequently, it is possible to load or unload fuel assemblies 20, preferably in the case 50, simultaneously through the three wells 32, 34, and 36.

[0061] As shown in Figure 5, the same movement step (step S2) is performed between two consecutive movements of the housing 40 via the carousel 30 (step S1), including operations performed on three wells 32, 34, and 36. In order to supply the fuel assemblies 20 to the reactor 10, the fuel assemblies 20 are removed from the housing 40 at reactor position 42 opposite to reactor well 32 (step S32a). In this step, an empty case 50 is left inside the housing 40, and in another step (step S32b), the fuel assemblies 20 are loaded into the housing 40 located at this reactor position. These are irradiated fuel assemblies 20 removed from the reactor core 18 of the reactor 10, and are introduced into the empty case 50. Simultaneously, the fuel assemblies 20 housed in the case 50 are loaded into the housing opposite to the supply well 34 at supply position 44 (step S34). This is typically a new fuel assembly 20 removed from the first storage chamber 2a, intended to be introduced into the reactor core 18 of the reactor 10 in a subsequent handling step after the fuel assembly 20 has been moved from the carousel 30. Simultaneously, a fuel assembly 20 housed in a case 50 is removed from the housing 40 at the discharge position 46 opposite the discharge well 36. This is an irradiated fuel assembly 20 that was previously recovered at the reactor position 42 opposite the reactor well 32 during a handling step prior to the movement of the housing 40 by the carousel 30 (step S1).

[0062] Following the path of housing 40 of carousel 30, the following operations can be described: a) Load the fuel assemblies 20 housed in the case 50 into the housing 40, typically the case 50 located inside the housing 40, via the supply well 34 from the carousel 30 at the supply position 44 (step S34). b) By rotating the carousel 30, the housing 40 is moved from the supply position 44 toward the reactor position 42 opposite to the reactor well 32 (step S1). c) Remove the fuel assembly 20 from the housing 40 at reactor position 42 via the reactor well 32 from the case 50 (step S32a), typically leaving the empty case 50 in the housing 40. d) Another fuel assembly 20 is loaded into the housing 40, typically in an empty case 50 within the housing 40, via the reactor well 32 at the reactor position 42 (step S32b). e) The rotation of the carousel 30 moves the housing 40 from the reactor position 42 to the discharge position 46 facing the discharge well 36 (step S1). f) Typically, the other fuel assembly 20 is removed from the housing 40 at the discharge position 46 via the discharge well 36 by removing the case 50 that houses the other fuel assembly 20 (step S36). g) The rotation of the carousel 30 moves the housing 40 from the discharge position 46 to the supply position 44 facing the supply well 34 (step S1).

[0063] Therefore, when the carousel 30 rotates three times, the housing 40 moves to three positions 42, 44, and 46, which correspond to three loading / unloading positions. At each of the positions 42, 44, and 46, the loading or unloading operation of the fuel assemblies can be performed without waiting for the other positions, which significantly reduces the time required to replace the fuel assemblies 20 in the core 18.

[0064] Figures 6a to 6h show the step of loading the irradiated fuel assemblies 20 into empty cases 50 at reactor position 42 opposite the reactor well 32. These steps can be performed when using a carousel 30 as described, or directly from the use of such a carousel 30, so that the cases 50 can be connected to the reactor well 30 by other means.

[0065] Well 32 includes a lower docking station 80 configured to cooperate with the upper part of case 50 by shape complementarity. The lower docking station 80 preferably protrudes into the transfer chamber 3 from its upper part 38. Well 32 also includes an upper docking station 82 configured to cooperate with the lower end of handling hood 60 by shape complementarity. The lower docking station 80 and the upper docking station 82 must ensure a sealed connection. The upper docking station 82 preferably protrudes into the reactor chamber 1 from plate 14. A docking station means any well device that enables the attachment of a handling hood in a plane perpendicular to the axis of the well (typically a horizontal plane), and preferably enables hermetically sealed communication with the well. The connection interface may include, for example, flanges, joints, grooves, etc., that act by having shape complementarity with the handling hood. Active components such as jaws or fastening elements may also be provided. The lower docking station 80 may include an electrical device that can heat and melt the metal that seals the plug 54.

[0066] In the example described below, an empty case 50, sealed and kept under an inert gas (e.g., argon), is placed inside the housing 40 of the carousel 30. The carousel 30 mounts the case 50 to the lower docking station 80. This is the situation shown in Figure 6a. The case 50 is sealed by a plug 54.

[0067] The reactor well 32 includes two slide valves V1, V2 configured to selectively seal the reactor well 32. Preferably, the first slide valve V1 is located below the upper part 38 of the transfer chamber 3, and the second slide valve V2 is located above the plate 14 of the reactor chamber 1. In the initial phase shown in Figure 6a, the two slide valves V1, V2 are closed, sealing the reactor well 32. The two slide valves V1, V2 define an intermediate region 84 of the reactor well 32 between them, which is isolated from both the transfer chamber 3 and the reactor chamber 1 as long as the slide valves V1, V2 are closed. This intermediate region 84 includes a recess 86 in which a movable element 90 is positioned. In the illustrated example, the movable element 90 is an electric trolley, but the movable element 90 may be any device that can selectively adopt a stowed position in which the movable element 90 has free passage within the reactor well 32, and an intercepted position in which the movable element is located in the passage of the reactor well 32 below the handling hood 60 when the handling hood 60 is connected to the reactor well 32. The movable element 90 can be, for example, a platform moved by an actuator.

[0068] Once case 50 is docked to the lower docking station 80, the handling hood 60 is moved and lowered by an overhead crane, as shown in Figure 6b, and then docked to the upper docking station 82. The two slide valves V1 and V2 of the reactor well 32 can then be opened to connect the lower docking station 80, the intermediate area 84, and the upper docking station 82. At the moment shown, slide valve V3, which closes the internal volume 63 of the handling hood 60, is closed, but it is subsequently opened to connect the internal volume 63 of the handling hood 60, the upper docking station 82, the intermediate area 84, and the lower docking station 80.

[0069] The plug 54 closes the case 50 again. The gripping member 62 is then lowered and reaches the plug 54 across the reactor well 32, more precisely, the gripping region 56 formed by the central cavity of the plug 54. The gripping member 62 works in cooperation with the gripping region 56 to grip the plug 54 and extend it through the reactor well 32, at least above the movable element 90. In the example shown in Figure 6c, the plug 54 rises to the internal volume of the handling hood 60, but can remain at a lower position, for example, at the height of the upper docking station 82.

[0070] The gripping member 62 releases the plug 54 or places the plug 54 on the movable element 90 in the recess 86, and the plug 54 is then pulled out to its housing position, freeing the passage of the reactor well 32 at the height of the intermediate region 84, as shown in Figure 6d. In the internal volume 63 of the handling hood 60, the gripping member 62 is removed and the slide valve V3 of the handling hood 60 is closed again. The second slide valve V2 is also closed again, isolating the intermediate region 84 and allowing the handling hood 60 to be disengaged from the reactor well 32. The handling hood 60 is then moved, as shown in Figure 6e, to collect the irradiated fuel assemblies 20 into the core 18 of the reactor 10 and return them to the opposite side of the reactor well 32.

[0071] The handling hood 60 is lowered and docked from the upper docking station 82 to the handling well 32, and the third slide valve V3 is opened, as with the second valve V2, connecting the internal volume 63 of the handling hood 60, where the fuel assembly 20 is positioned and held by the gripping member 62, to the handling well 32. The fuel assembly 20 is lowered through the reactor well 32 to the case 50 by the gripping member 62, as shown in Figure 6f.

[0072] When the fuel assembly 20 comes to rest inside the case 50, the gripping member 62 releases the fuel assembly 20 and rises into the handling hood 60. Next, the movable element 90, which also carries the plug 54, is positioned in the reactor well 32 below the handling hood 60 by rotating its wheels, as shown in Figure 6g. Then, the gripping member 62 descends and grips the plug 54 on the movable element 90 in the same manner as described above. Next, preferably after the plug 54 has been lifted by the gripping member 62, the movable element 90 is removed. Then, the gripping member 62 is lowered and passed through the reactor well 32, and the plug 54 is repositioned on the case 50 and released, as shown in Figure 6h. All that remains is to reassemble the gripping member 62 into the handling hood 60. Next, the slide valves V1, V2 of the reactor well 32 and the slide valve V3 of the handling hood 60 are closed. The case 50 can be removed from the reactor well 32, for example, from the lower docking station 80. The carousel 30 then moves the housing supporting the case 50 toward the discharge position 46 facing the discharge well 36, enabling the discharge of the irradiated fuel assembly 20.

[0073] The rotation of the carousel 30 allows the case 50 containing the already preheated new fuel assembly 20 to be positioned below the reactor well 32, ready to be removed along with the handling hood 60 and introduced into the reactor 10. Once this new fuel assembly 20 is removed, the case 50 becomes empty and can be used in the manner described above. Only for the first irradiated fuel assembly 20 removed from the core 18 does it become necessary to transport the empty case 50 to make space in the core 18 into which the fuel assembly 20 can be inserted, and thus the case 50 remains empty.

[0074] Referring to Figures 7a to 7d, an example of removing a new fuel assembly 20 from case 50 is illustrated. Many of the features previously described will not be described again, but may be present. As previously stated, these steps can be carried out using a carousel 30 as described, or they can be carried out directly using such a carousel 30, and thus case 50 can be connected to the reactor well 30 by other means.

[0075] As shown in Figure 7a, the case 50 containing the new fuel assembly 20 is transported to the reactor position on the opposite side of the reactor well 32. The case 50 is docked to the lower docking station 80, and the slide valve V3 of the handling hood 60 opens, as does the second slide valve V2 of the reactor well 32. The first valve V1 can be temporarily kept closed.

[0076] When the first valve V1 is opened, the gripping member 62 grips the plug 54 and reassembles it, as shown in Figure 7b. Then, as shown in Figure 7c, the movable element 90 is positioned below the handling hood 60 within the passage of the reactor well 32 to retrieve the plug 54 that was released or positioned by the gripping member 62, releasing the plug 54 from the passage and pulling it out. Next, the gripping member 62 is lowered to grip the fuel assembly 20 and reassemble it within the handling hood 60. Then, as shown in Figure 7d, the valve V3 of the handling hood 60 is closed again, as is the second valve V2 of the reactor well 32. The handling hood 60 can then be removed from the reactor well 32 and the fuel assembly 20 can be placed into the reactor core 18 of the reactor 10. Then, as described above with reference to Figures 6e to 6h, another irradiated fuel assembly 20 can be brought back and loaded into the case 50.

[0077] In these examples, the gripping member 62 is used both for handling the fuel assembly 20 and for removing the plug 54 from the case. However, it is possible to use two dedicated gripping members 62, namely one gripping member for handling the plug 54 and another gripping member for handling the fuel assembly 20.

[0078] Similar processing is performed at the heights of the supply well 34 and the discharge well 36. However, the procedure can be simplified unless the reactor 10 is housed in the storage area 2. In particular, handling via the supply well 34 and the discharge well 36 does not imply the need to remove the plug 54: that is, the case 50 containing the fuel assembly 20 and closed by its plug 54 is loaded into the housing 40 via the supply well 34 and removed via the discharge well 36.

[0079] To accomplish this, a transfer station 100 is provided within each storage area 2, and typically within a case 50, the fuel assemblies can be transferred between the inside of the housing 40 of the carousel 30 and a location within the storage area 2, such as a receiving basket. Each transfer station 100 is equipped with means for lifting and moving the case 50, such as a winch and a gripping device attached to the free end of the winch chain, or an overhead crane.

[0080] For example, the transfer station 100 may consist of the following main elements: - Upper section 102 for docking with the overhead crane 104, including a hook connected to the overhead crane 104 by a chain or cable. - A main body 106 that forms a sheath for receiving the case 50 or fuel assembly 20 during transport.

[0081] Case 50, containing the fuel assembly 20, is gripped by a grappling hook and gradually raised and lowered by a chain driven by a winch. The lifting chain is designed to handle the fuel assembly / case reliably. The winch is equipped with overload and overspeed detectors.

[0082] To access wells 34 and 36, the grappling hook of the transfer station 100 is gradually lowered to the height of the housing 40, bringing the case 50 into contact with the support edges positioned around the openings of wells 34 and 36. The transfer station 100, gripping the case 50 containing the fuel assemblies 20, is moved horizontally by the overhead crane 104 and transported toward storage equipment 110, such as baskets in the storage room 2.

[0083] In particular, when loading a new fuel assembly 20 into the housing 40 at the supply position 44, the case 50 can be heated. Preferably, a temperature of at least 200°C is achieved inside the case 50 before the case 50 is moved to the reactor position 42. Such heating makes it possible to avoid thermal shock to the fuel assembly 20, in particular, when the fuel assembly 20 is introduced into the core 18 of the reactor 10.

[0084] The present invention is not limited to the embodiments described and illustrated in the accompanying drawings. In particular, modifications are possible in terms of constituting different technical features or by substituting technical equivalents without departing from the scope of protection of the invention.

Claims

1. A fuel assembly handling system for moving fuel assemblies (20) between a reactor chamber (1) configured to house a nuclear reactor (10) and a storage chamber (2) configured to store fuel assemblies (20), The handling system includes a carousel installed in a transfer chamber (3), the transfer chamber (3) communicating with the reactor chamber (1) via a reactor well (32), the first storage chamber (2a) via a first storage well (34), and the second storage chamber (2b) via a second storage well (36), the carousel (30) including a plurality of housings (40), each housing (40) configured to accommodate the fuel assemblies (20), and the carousel (30) is configured to move the housings (40) between a reactor position (42) facing the reactor well (32), a second position (44) facing the first storage well (34), and a third position (46) facing the second storage well (36) within the transfer chamber (3).

2. The system according to claim 1, wherein the reactor well (32) extends between the reactor chamber (1) and the upper part (38) of the transfer chamber (3), and each of the storage wells (34, 36) extends between the storage chamber (2) and the upper part (38) of the transfer chamber (3).

3. The system according to claim 1, wherein the carousel (30) comprises a shaft (47) configured to rotate the housing (40), the housing (40) being evenly distributed around the shaft (47) at a certain angular offset in the plane of rotation, and the reactor (32) and storage wells (34, 36) being evenly distributed around the shaft (47) at the same angular offset.

4. The system according to claim 1, wherein the carousel (30) comprises a housing support (31) that houses the housing (40) and is displaceable along the shaft (47) to change the height of the housing (40) within the transport chamber (3).

5. The system according to claim 1, comprising a plurality of cases (50) configured to be received within the housing (40) of the carousel (30), each case (50) configured to house the fuel assembly (20), and comprising a removable plug (54) configured to seal the case (50) when the fuel assembly (20) is present in the case (50).

6. The system according to claim 5, wherein each case (50) is provided with a heating device for heating the case (50).

7. The system according to claim 5, comprising a handling hood (60) that is movable within the reactor chamber (1) and configured to dock with the reactor well (32), the handling hood (60) extending through the reactor well (32) and comprising a gripping member (62) adapted to grip and lift the plug (54) of the case (50).

8. The system according to claim 7, further comprising a movable member (90) configured to selectively position itself within the reactor well (32) below the handling hood (60) when the handling hood (60) is fixed to the reactor well (32), wherein the movable member (90) is configured to receive the plug (54) of the case (50).

9. The system according to claim 8, wherein the reactor well (32) comprises two slide valves (V1, V2) configured to selectively seal the reactor well (32), and the movable member (90) is positioned between the two slide valves.

10. A nuclear power plant comprising a reactor chamber (1) for housing a reactor (10) and at least two storage areas (2) for storing fuel assemblies (20), wherein the nuclear power plant is equipped with the fuel assembly handling system described in claim 1.

11. A method for handling a fuel assembly (20) between a reactor chamber (1) configured to house a nuclear reactor and two storage chambers (2) configured to store fuel assemblies (20), using the fuel assembly handling system described in claim 1, a) Loading the fuel assembly (20) into the housing (40) of the carousel (30) at the second position (44) via the first storage well (34), (b) The step of moving the housing (40) from the second position (44) to the reactor position (42) opposite the reactor well (32) by rotating the carousel (30), c) The step of removing the fuel assembly (20) from the housing (40) to the reactor position (42) via the reactor well (32), d) Loading another fuel assembly (20) into the housing (40) at the reactor position (42) via the reactor well (32), e) The step of moving the housing (40) from the reactor position (42) to a third position (46) opposite to the second storage well (36) by rotating the carousel (30), f) The step of removing the other fuel assembly (20) from the housing (40) at the third position (46) via the second storage well (36), g)) The step of moving the housing (40) from the third position (46) to the second position (44) opposite the first storage well (34) by rotating the carousel (30), A method that includes this.

12. The method according to claim 11, wherein, between two consecutive displacements (S1) of the housing (40) by the carousel (30), the fuel assembly (20) is removed from the housing (40) at the reactor position (42) (S32a), the fuel assembly (20) is loaded into the housing (40) positioned at the reactor position (42) (S32b), the fuel assembly (20) is loaded into the housing (40) at the second position (44) (S34), and the fuel assembly (20) is removed from the housing (40) at the third position (46) (S36).

13. The method according to claim 11, wherein the case (50) housed within the housing (40) is enclosed in an inert atmosphere when at least the plug (54) closes the case (50) and the case (50) houses the fuel assembly.

14. - The steps include docking the case (50) inside the transfer chamber (3) into the well connecting the transfer chamber (3) and the reactor chamber (1) containing the reactor (10), and closing the case (50) with a plug (54), - The gripping member (62) of the handling hood (60), which is docked to the reactor well (32) of the reactor room (1), enters the reactor well (32) and grips the plug (54), - The movable element (90) is positioned in the reactor well (32) below the handling hood (60) to receive the plug (54), - The steps of retracting the movable element (90) to clear the passage of the reactor well (32), - The fuel assembly (20) passes through the reactor well (32) and is removed from the casing (50) or placed in the casing (50), The method according to claim 11, including the method described in claim 11.

15. - The steps of positioning the movable element (90) that supports the plug (54) in the reactor well (32) below the handling hood (60), - The step of inserting the gripping member (62) into the reactor well (32) and gripping the plug (54), - The steps of retracting the movable element (90) to clear the passage of the reactor well (32), - The steps of inserting the gripping member (62) into the reactor well (32), replacing the plug (54), and closing the case (50), The method according to claim 14, including the method described in claim 14.

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