Fuel assembly maintenance devices and related assemblies and maintenance methods

Abstract

The present invention relates to a maintenance device (40) for a fuel assembly in a nuclear reactor, the assembly comprising: - a plurality of guide tubes, each capable of receiving a neutron absorber rod and including at least one connection system; and - a top end piece (16) defining a plurality of through pipes (22), which is through and capable of receiving the connection system of one of the guide tubes. The maintenance device (40) includes: - a tool (42) capable of locking or unlocking one of the guide tubes relative to the top end piece by rotating the connection system (26) in the associated pipe (22); and - a movable cover (44) capable of being configured to face the top end piece (16) and including a plate (54) defining at least one opening (56) capable of guiding the tool (42) to dock with the pipe (22) associated with the connection system (26).

Description

Technical Field

[0001] This invention relates to a maintenance device for nuclear reactor fuel assemblies.

[0002] The present invention also relates to an assembly comprising a fuel assembly of a nuclear reactor and such maintenance device.

[0003] The present invention also relates to a maintenance method for such an assembly. Background Technology

[0004] Specifically, the nuclear reactor is a pressurized water reactor (REP or PWR). However, this invention is also applicable to fast neutron reactors.

[0005] A nuclear reactor includes a core, which comprises multiple nuclear fuel assemblies arranged side-by-side within a reactor vessel.

[0006] Each fuel assembly typically includes nuclear fuel rods and a pilot tube. The reactor also includes control rods, each equipped with multiple absorber rods configured to be inserted into or removed from the pilot tube to control the reactor's reactivity.

[0007] When performing maintenance operations on the fuel assembly, such as replacing a defective fuel rod, it is necessary to remove the top end of the assembly. In particular, it is necessary to unlock the connection system between the top end and the guide tube.

[0008] It is known that this operation is achieved by means of a tool actuated by an operator under visual control via a camera.

[0009] Because the components are underwater, the distance between the operator and the components is greater than 5 meters. This operation is complex and time-consuming, and can only be performed by highly skilled and well-trained operators.

[0010] Therefore, unlocking the connection system is random, non-repeating, and depends on the operator.

[0011] The same problem also exists when locking the top end piece after maintenance is performed. Summary of the Invention

[0012] Therefore, the object of the present invention is to provide a maintenance device that allows for easy and quick locking / unlocking of the top end piece while ensuring good accuracy and repeatability.

[0013] Therefore, the present invention relates to a maintenance device for a fuel assembly of a nuclear reactor, the fuel assembly including a plurality of guide tubes, each guide tube capable of receiving a neutron absorber rod and including at least one connection system disposed at an end of the guide tube; and a top end member defining a plurality of through pipes, each through pipe capable of receiving the connection system of one of the guide tubes; the maintenance device includes a tool including a body elongated along a main axis and capable of locking or unlocking at least one guide tube relative to the top end member by rotating the connection system of the guide tube in the associated pipe about the main axis; and a removable cover portion capable of being configured to face the top end member and including a plate defining at least one opening that guides the tool to dock with the pipe associated with the connection system.

[0014] Because the tool is guided by the cover, the alignment of the tool with the guide tube is greatly facilitated, allowing locking / unlocking to be faster and easier to repeat, without requiring a highly skilled operator.

[0015] According to a particular embodiment, the maintenance device includes one or more of the following features:

[0016] - The tool has a long, narrow body with a hollow cylindrical end that defines at least one notch, and wherein the tool includes a centering rod that projects out of the cylindrical end along the main axis, the notch and the centering rod being able to engage with one of the connecting systems to allow the connecting system to rotate;

[0017] - The tool includes a column that protrudes laterally from the elongated body relative to the main axis and is able to restrict the translational movement of the tool along the main axis in the opening;

[0018] - For each opening, the plate includes a stop that projects radially from the plate and extends over a portion of the periphery of the opening, the stop engaging with a tool's stud to restrict rotational movement of the tool about its main axis; and

[0019] - For each opening, the plate defines a slot that extends radially from the opening and is capable of receiving a tool block.

[0020] The present invention also relates to an assembly comprising a fuel assembly of a nuclear reactor, the fuel assembly including a plurality of guide tubes, each guide tube being capable of receiving a neutron absorber rod and including at least one connection system disposed at an end of said guide tube; and a top end member defining a plurality of through-channels, each channel being capable of receiving a connection system of one of the guide tubes; and a maintenance device for maintaining said fuel assembly as described above, the maintenance device being configured to switch from a passive configuration to an active configuration, in which tools and a cover are configured to be separate from the fuel assembly, and in the active configuration, the cover is configured to face the top end member and the tools are guided by associated openings to engage with one of the connection systems.

[0021] According to a particular embodiment, the maintenance device includes one or more of the following features:

[0022] - The cover includes an opening for each guide tube, and each opening in the active configuration faces the pipe associated with the guide tube;

[0023] - A connecting system sleeve comprising at least one protrusion projecting laterally relative to a guide tube, wherein a top end member defines a groove, the sleeve being convertible from a locking configuration to an unlocking configuration, in which the groove receives the protrusion and prevents translational movement between the guide tube and the conduit along a main axis; and in the unlocking configuration, the protrusion disengages from the groove, and a tool is capable of converting the sleeve from one configuration to the other by rotating the sleeve about the main axis; and

[0024] - This tool can change the configuration of a ring from one type to another by rotating the ring between 70° and 110° around the main axis.

[0025] The present invention also relates to a maintenance method for the assembly as defined above, comprising the following steps:

[0026] - Position the cover facing the top end piece of the fuel assembly;

[0027] -Insert the tool into one of the openings in the cover and mate the tool with the corresponding guide tube; and

[0028] - Rotate the connection system of the guide tube in the relevant pipeline and lock / unlock the guide tube relative to the top end piece. Attached Figure Description

[0029] Other features and advantages of the invention will become apparent from the following detailed description, which is illustrative and not limiting, and refers to the accompanying drawings, wherein:

[0030] [ Figure 1 ]- Figure 1 This is a partial side view of the assembly according to the present invention.

[0031] [ Figure 2 ]- Figure 2 Is with Figure 1 A perspective view of the tool assembly and the covered section.

[0032] [ Figure 3 ]- Figure 3 yes Figure 2 A top view of the covered part.

[0033] [ Figure 4 ]- Figure 4 yes Figure 2 A perspective view of the tool.

[0034] [ Figure 5 ]- Figure 5 yes Figure 1 A perspective view of the assembly's connection system; and

[0035] [ Figure 6 ]- Figure 6 yes Figure 1 A horizontal cross-sectional view of the top end component of the assembly. Detailed Implementation

[0036] A nuclear reactor consists of a primary loop in which primary fluids circulate and a secondary loop in which secondary fluids circulate.

[0037] The primary loop includes a vessel, at least one steam generator, and a primary pump. The vessel includes a lid and a core housed inside the vessel. The primary fluid is heated in the reactor vessel by contact with the core and then directed to the steam generator. In the steam generator, it releases a portion of its thermal energy to the secondary fluid.

[0038] The secondary fluid enters the steam generator in a liquid state and vaporizes under the influence of the heat energy received from the primary fluid. It then leaves the steam generator in a steam state and is directed toward the turbine to generate electricity.

[0039] The reactor core comprises multiple fuel assemblies 10.

[0040] For example, a nuclear reactor with an electric power of 900 MWe includes 157 fuel assemblies 10, a reactor with an electric power of 1450 MWe (the so-called "N4" reactor) includes 205 fuel assemblies 10, and a reactor with an electric power of 1600 MWe (the so-called "EPR" reactor) includes 241 fuel assemblies 10.

[0041] Reference Figure 1 Each fuel assembly 10 includes a bundle of fuel rods 12, which is inserted into the support structure 14, also known as the frame.

[0042] Each fuel rod 12 extends along the vertical axis A-A'.

[0043] For example, each fuel assembly 10 includes 264 fuel rods 12. For clarity, Figure 1 Only two fuel rods 12 are shown in the image.

[0044] Each fuel rod 12 includes an outer tube, which is preferably made of zirconium and has a diameter of approximately 1 cm.

[0045] Each tube contains multiple nuclear fuel particles, totaling 272 particles.

[0046] The supporting structure 14 includes a bottom end piece 16, a top end piece 16, a guide tube 18, and a spacer mesh 20 (not shown).

[0047] Fuel rod 12 is positioned between two end pieces.

[0048] The distance between the top end piece 16 and the bottom end piece along the vertical axis A-A' is greater than 4m.

[0049] Advantageously, the horizontal cross-section of each end piece is a square with a length approximately equal to 20 cm.

[0050] like Figure 2 As can be seen, the top end piece 16 defines multiple through pipes 22.

[0051] Each pipe 22 can receive one of the guide pipes 18.

[0052] like Figure 6 As can be seen, the top end piece 16 defines a groove 23 for each pipe 22. Each groove 23 is provided in the relevant pipe 22 and extends around the outer contour of the pipe 22 in the horizontal section.

[0053] Each groove 23 has at least one notch 24, particularly notches 24 with opposite diameters.

[0054] The spacer mesh 20 is fixed to the guide tube 18 and distributed along the guide tube 18 between the top end piece 16 and the bottom end piece.

[0055] The spacer 20 is able to hold the fuel rods 12 in the proper position.

[0056] Advantageously, the fuel assembly 10 includes 24 guide tubes 18.

[0057] Each guide tube 18 includes an upper end portion that can be connected to the top end piece 16 and a lower end portion that can be connected to the bottom end piece.

[0058] Therefore, each guide tube 18 connects two end pieces and ensures the rigidity of the load-bearing structure 14.

[0059] Each guide tube 18 is capable of receiving absorber rods (not shown) and absorbing neutrons present in the core to mitigate the reactivity of the nuclear reactor core.

[0060] Each guide tube 18 includes at least one connection system 26 disposed at the upper end of the guide tube 18.

[0061] In advantageous embodiments, such as Figure 5 It can be seen that the connecting system 26 is a ring that limits the internal volume 27.

[0062] Then, the connection system 26 includes an elongated body 28, at least one protruding pin 30, at least one support member 32, and at least one shoulder 34.

[0063] The elongated body 28 extends in the same direction as the associated guide tube 18, and advantageously extends along the main axis A-A'.

[0064] The elongated body 28 is configured to surround the upper end of the guide tube 18.

[0065] like Figure 5 It is evident that the ring sleeve advantageously includes two protruding pins 30 with opposite diameters.

[0066] Each protrusion 30 protrudes laterally relative to the elongated body 28 in a direction orthogonal to the vertical axis A-A'.

[0067] Each protrusion 30 can slide in the groove 23 by rotating about the main axis A-A'.

[0068] In particular, the protruding pin 30 is supported by a ring 29 that is capable of rotating about the main axis A-A' relative to the elongated body 28.

[0069] The connection system 26 can switch from a locked configuration to an unlocked configuration.

[0070] In a locked construction, such as Figure 6 As can be seen, the groove 23 receives the protrusion 30 and prevents translational movement between the guide tube 18 and the pipe 22 along the vertical axis A-A'.

[0071] When at least one connection system 26 of component 10 is in a locked configuration, the top end piece 16 and the other parts of component 10 are mechanically connected and it is impossible to remove the top end piece 16.

[0072] exist Figure 5 In the visible unlocking mechanism, the protruding pin 30 separates from the groove 23 at one of the notches 24. Therefore, the guide tube 18 and the pipe 22 can translate along the vertical axis A-A'.

[0073] When all connection systems 26 are in the unlocked configuration, the top end piece 16 is free relative to the rest of the assembly 10 and can then be removed for maintenance operations.

[0074] like Figure 5 It is evident that the ring sleeve advantageously comprises two support members 32 with opposite diameters.

[0075] Each support member 32 protrudes laterally from the elongated body 28 relative to the main axis A-A'.

[0076] like Figure 5As can be seen, each support 32 can engage with the protruding pin 30 in the unlocking configuration of the ring so as to hold the ring in the unlocking configuration during maintenance operations.

[0077] Advantageously, each support 32 is flexible to allow the pin 30 to be released from the support 32 when the ring is changed to the locking configuration.

[0078] In the locked configuration, the protruding pin 30 and the associated support 32 are separated from the vertical axis A-A' by an angle between 70° and 110°, preferably substantially equal to 90°.

[0079] like Figure 5 It is evident that the ring advantageously includes four protruding shoulders 34 regularly arranged around the elongated body 28.

[0080] Each shoulder 34 protrudes laterally from the elongated body 28 relative to the main axis A-A'.

[0081] like Figure 1 As can be seen, each shoulder 34 can mate with the lower portion of the top end piece 16 to restrict the introduction of the guide tube 18 into the pipe 22.

[0082] A maintenance device 40 for fuel assembly 10 will now be introduced.

[0083] like Figure 2 As can be seen, the maintenance device 40 includes a tool 42 and a cover 44.

[0084] As in Figure 4 More specifically, tool 42 includes a long strip body 46 along the main axis B-B', a centering rod 48, and a column block 50.

[0085] Advantageously, tool 42 extends along the main axis B-B' for a length greater than 5m, particularly 6m.

[0086] The diameter of the elongated body 46 is preferably between 10 mm and 30 mm.

[0087] The elongated body 46 has a hollow cylindrical end 51 that defines at least one notch 52, preferably two notches 52 with opposite diameters.

[0088] Each notch 52 and centering rod 48 can engage with one of the connection systems 26 to allow rotation of the connection system 26.

[0089] Specifically, each notch 52 is capable of receiving one of the protrusions 30 of the connection system 26 to allow rotation of the connection system 26.

[0090] The centering rod 48 protrudes along the main axis B-B' to the outside of the cylindrical end 51, advantageously exceeding 5 cm in length.

[0091] The centering rod 48 can penetrate into the internal volume 27 of the connection system 26 to facilitate the engagement between the notch 52 and the protrusion 30.

[0092] like Figure 4 The column block 50 protrudes laterally from the elongated body 46 relative to the main axis B-B'.

[0093] The block 50 can restrict the translational movement of the tool 42 relative to the cover 44 along the main axis B-B'.

[0094] like Figure 3 The middle component, the cover portion 44, can be removably configured to face the top end component 16.

[0095] The covering portion 44 includes a fixing device 53 and a plate 54 defining at least one opening 56.

[0096] The fixing device 53 is configured to allow the cover 44 to be reversibly fixed on the top end piece 16.

[0097] Advantageously, such as Figure 2 As can be seen, the cover portion 44 includes an opening 56 for each guide tube 18, and in particular, multiple openings 56.

[0098] Each opening 56 allows the tool 42 to dock with the pipe 22 associated with the connection system 26.

[0099] The diameter of each opening 56 is approximately equal to the diameter of the elongated body 46 of the tool 42, specifically between 20 mm and 25 mm.

[0100] Advantageously, the thickness of plate 54 is between 10 mm and 20 mm and extends over an upper width between 20 mm and 30 mm.

[0101] For each opening 56, plate 54 includes a stop 58 that projects radially from plate 54 along the vertical axis A-A'.

[0102] Each stop 58 extends over a portion of the periphery of the opening 56, advantageously extending within an angular range between 90° and 180°.

[0103] like Figure 4 It can be seen that each stop 58 can cooperate with the column block 50 of the tool 42 to restrict the rotational movement of the tool 42 around the main axis B-B'.

[0104] Plate 54 defines a slot 60 for each opening 56 that extends radially from the opening 56 and is capable of receiving a block 50 of tool 42.

[0105] Each slot 60 is separated from the associated stop 58.

[0106] The maintenance device 40 is configured to switch from a passive configuration to an active configuration.

[0107] In the passive configuration, tool 42 and cover 44 are positioned separately from fuel assembly 10.

[0108] In active construction, such as Figure 1 and Figure 2 As shown, the cover 44 is positioned to face the top end piece 16 and the tool 42 engages with one of the connection systems 26 via the associated opening 56.

[0109] In the active configuration, each opening 56 faces the conduit 22 associated with the guide tube 18.

[0110] Then, the vertical axis A-A' and the principal axis B-B' are roughly parallel.

[0111] In an active configuration, tool 42 can lock or unlock at least one of the guide tubes 18 relative to the top end piece 16 by rotating connection system 26 relative to the main axis B-B' of guide tube 18 in associated conduit 22.

[0112] In particular, tool 42 can transform the connection system 26 from one configuration to another by rotating the ring about the main axis B-B' between 70° and 110°.

[0113] A method for maintaining fuel assembly 10 using maintenance device 40 will now be described.

[0114] Initially, the nuclear reactor was operational.

[0115] Alternatively, the reactor is shut down for maintenance operations.

[0116] Then, remove the container lid and absorber rod to make the underwater fuel assembly 10 accessible.

[0117] Hereafter, only maintenance operations for a single component 10 will be described. However, those skilled in the art will understand that the process is applicable to any number of fuel assemblies 10.

[0118] like Figure 6 As shown, all the loops in component 10 are initially in a locked configuration. Therefore, it is impossible for the operator to remove the top end piece 16.

[0119] The maintenance device 40 is initially in a passive position.

[0120] Then, the cover portion 44 is positioned facing the top end piece 16 of the component 10 and is fixed to the top end piece 16 by the fixing device 53.

[0121] Then, the operator inserts tool 42 into one of the openings 56 of the cover 44.

[0122] The maintenance device 40 is therefore in an active configuration.

[0123] Opening 56 guides tool 42 to translate along the vertical axis A-A'.

[0124] The centering rod 48 of tool 42 is gradually introduced into the pipe 22 of the relevant top end piece 16.

[0125] When the cylindrical end 51 of tool 42 abuts against the annulus of guide tube 18 present in pipe 22, the operator rotates tool 42 about the main axis B-B' until the cylinder 50 contacts the stop 58 associated with opening 56, as shown. Figure 2 As shown.

[0126] Then, the operator rotates tool 42 in the opposite direction around the main axis B-B' until the column 50 contacts the stop 58 again.

[0127] Therefore, even in the locked position, where there is an angular offset between the slot and the protrusion 30, the notch 52 in the tool 42 can still ensure a fit with the protrusion 30 of the ring.

[0128] Therefore, the ring is in the unlocked configuration and the translation of the guide tube 18 and the top end piece 16 along the vertical axis A-A' is no longer mechanically constrained by each other.

[0129] Specifically, the protruding pin 30 is separated from the groove 23 and is located at the recess 24.

[0130] The weight of the tool 42 itself allows sufficient pressure to be applied to deform the support 32 and engage the pin 30 with the support 32.

[0131] Then, as Figure 5 As shown, the support 32 engages with the protrusion 30 in the unlocked position and allows the ring to be held in that position.

[0132] Then, the operator no longer applies vertical pressure through tool 42.

[0133] Then, the operator removes tool 42 from pipe 22 and then from opening 56.

[0134] Then, the operator repeats the above steps for each opening 56 of the cover 44.

[0135] Therefore, the operator changed all the connection systems 26 from a locked configuration to an unlocked configuration.

[0136] Then, the cover 44 separates from the top end piece 16 and the maintenance device 40 is switched to a passive configuration.

[0137] The operator can choose to visually control the loop by using a camera located above component 10 to confirm that the loop is in the unlocked position.

[0138] Therefore, the top end piece 16 is no longer connected to the other parts of component 10.

[0139] Then, the top end piece 16 is removed and placed separately from component 10.

[0140] The operator can then access fuel rod 12 or guide tube 18 for maintenance.

[0141] For example, during maintenance operations, at least one fuel rod 12 is replaced.

[0142] When the maintenance operation is completed, the top end piece 16 is placed back on top of the assembly 10.

[0143] Then, the cover portion 44 is configured to face the top end piece 16 of the component 10.

[0144] Then, the operator inserts tool 42 into one of the openings 56 of the cover 44.

[0145] The maintenance device 40 is therefore in an active configuration.

[0146] Opening 56 guides tool 42 to translate along the vertical axis A-A'.

[0147] The centering rod 48 of tool 42 is gradually introduced into the pipe 22 of the relevant top end piece 16.

[0148] When the cylindrical end 51 of tool 42 abuts against the annulus of guide tube 18 present in pipe 22, the operator rotates tool 42 about the main axis B-B' until the cylinder 50 contacts the stop 58 associated with opening 56, as shown. Figure 2 As shown.

[0149] Then, the operator rotates the tool 42 in the opposite direction around the main axis B-B' until the slot 60 of the cover part 44 receives the column block 50.

[0150] Then, the loop is in a locked configuration.

[0151] Specifically, the weight of the tool 42 itself allows sufficient pressure to be applied to deform the support 32 and remove the protrusion 30 from the support 32.

[0152] The groove 23 receives the protrusion 30 and prevents translational movement between the guide tube 18 and the pipe 22 along the vertical axis A-A'.

[0153] The operator then removes tool 42 from pipe 22 and then from opening 56.

[0154] Then, the operator repeats the above steps for each opening 56 of the cover 44.

[0155] Therefore, the operator changed all connection systems 26 from an unlocked configuration to a locked configuration.

[0156] Then, the cover 44 separates from the top end piece 16 and the maintenance device 40 is switched to a passive configuration.

[0157] Advantageously, the operator can use a camera positioned above component 10 for visual control to verify that the loop is in the locked position.

[0158] Then, the container lid is placed back in its proper position on the container, and the reactor can be run again.

[0159] As can be seen, this invention has many advantages.

[0160] In fact, the present invention allows for easy and quick removal of the top end piece 16 for maintenance operations.

[0161] The operator of tool 42 is guided by cover 44, and alignment of the tool with the guide tube is thus facilitated. Therefore, the maintenance device 40 according to the invention avoids the time loss that is usually caused by the operator's trial and error when attempting to align the tool with the ring.

[0162] Furthermore, this invention allows for easily repeatable locking / unlocking without requiring highly skilled operators. This improves the safety and availability of the power station.

[0163] Specifically, the cover 44 allows for proper positioning of the tool 42, thus ensuring optimal alignment with the connection system 26; and allows the tool to be positioned at a suitable height so as not to apply excessive pressure. Therefore, the cover 44 prevents damage to the connection system 26 and the conduit 22, which improves the service life of the guide tube 18.

[0164] Finally, the stop 58 and the slot 60 allow for precise locking / unlocking of the connection system 26 without the need for visual control.

Claims

1. A maintenance device (40) for a fuel assembly (10) of a nuclear reactor, the fuel assembly (10) comprising: - A plurality of guide tubes (18), each guide tube (18) being capable of receiving a neutron absorber rod and including at least one connection system (26) disposed at the end of the guide tube (18); and - Top end piece (16) defining a plurality of through pipes (22), each pipe (22) being able to receive a connection system (26) of one of the guide pipes (18); Its features are, The maintenance device (40) includes: - Tool (42), comprising an elongated body (46) along a main axis (B-B') and capable of locking or unlocking at least one of the guide tubes (18) relative to the top end piece (16) by rotating the connecting system (26) of the guide tubes (18) in the associated conduit (22) about the main axis (B-B'); and - A movable cover (44) that can be configured to face the top end piece (16) and includes a plate (54) defining at least one opening (56) that can guide the tool (42) to dock with a pipe (22) associated with the connection system (26). The tool (42) includes a column (50) that protrudes laterally from the elongated body (46) relative to the main axis (B-B') and is able to restrict the translational movement of the tool (42) along the main axis (B-B') in the opening (56); Furthermore, the plate (54) includes a stop (58) for each opening (56), the stop protruding radially from the plate (54) and extending over a portion of the periphery of the opening (56), the stop (58) being able to engage with the column (50) of the tool (42) to restrict the rotational movement of the tool (42) about the main axis (B-B').

2. The maintenance device (40) according to claim 1, wherein, The elongated body (46) of the tool (42) has a hollow cylindrical end (51) defining at least one notch (52), and wherein the tool (42) includes a centering rod (48) projecting out of the cylindrical end (51) along the main axis (B-B'), the notch (52) and the centering rod (48) being capable of engaging with one of the connecting systems (26) to allow the connecting system (26) to rotate.

3. The maintenance device (40) according to claim 1, wherein, The plate (54) defines a slot (60) for each opening (56), the slot extending radially from the opening (56) and capable of receiving the block (50) of the tool (42).

4. The maintenance device (40) according to claim 1, wherein, Each stop (58) extends within an angular range of 90° and 180°.

5. An assembly comprising: - A fuel assembly (10) for a nuclear reactor, said fuel assembly (10) comprising: + Multiple guide tubes (18), each guide tube (18) is capable of receiving a neutron absorber rod and includes at least one connection system (26) disposed at the end of the guide tube (18); as well as + Top end piece (16), which defines a plurality of through pipes (22), each pipe (22) being able to receive a connection system (26) of one of the guide pipes (18); - A maintenance device (40) for the fuel assembly (10), the maintenance device being the maintenance device according to claim 1, the maintenance device (40) being configured to transition from a passive configuration to an active configuration, in which the tool (42) and the cover (44) are configured to be separate from the fuel assembly (10), and in the active configuration, the cover (44) is configured to face the top end piece (16) and the tool (42) engages with one of the connection systems (26) by being guided by an associated opening (56). The tool (42) includes a column (50) that protrudes laterally from the elongated body (46) relative to the main axis (B-B') and is able to restrict the translational movement of the tool (42) along the main axis (B-B') in the opening (56); Furthermore, the plate (54) includes a stop (58) for each opening (56), the stop protruding radially from the plate (54) and extending over a portion of the periphery of the opening (56), the stop (58) being able to engage with the column (50) of the tool (42) to restrict the rotational movement of the tool (42) about the main axis (B-B').

6. The assembly according to claim 5, wherein, The cover (44) includes an opening (56) for each guide tube (18), and each opening (56) in the active configuration faces the pipe (22) associated with the guide tube (18).

7. The assembly according to claim 5, wherein, The connection system (26) is a ring sleeve comprising at least one protrusion (30) that protrudes laterally relative to the guide tube (18), wherein the top end piece (16) defines a groove (23), the ring sleeve being capable of changing from a locking configuration to an unlocking configuration, in which the groove (23) receives the protrusion (30) and prevents translational movement between the guide tube (18) and the pipe (22) along the main axis (B-B'), and in the unlocking configuration, the protrusion (30) is separated from the groove (23), and the tool (42) is capable of changing the ring sleeve from one configuration to another by rotating the ring sleeve about the main axis (B-B').

8. The assembly according to claim 7, wherein, The tool (42) can change the ring from one configuration to another by rotating the ring about the main axis (B-B') between 70° and 110°.

9. A maintenance method for an assembly, said assembly being the assembly according to claim 5, the maintenance method comprising the following steps: - The cover (44) is configured to face the top end piece (16) of the fuel assembly (10); - Introduce the tool (42) into one of the openings (56) of the cover (44) and mate the tool (42) with the corresponding guide tube (18); and - Rotate the connection system (26) of the guide tube (18) in the associated pipe (22) and lock / unlock the guide tube (18) relative to the top end piece (16).

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