Maintenance tool comprising a nut retainer

Abstract

This maintenance tool (1) comprises a carrying ring (5) and a nut retainer (7), the carrying ring (5) comprising a chamber (9) opened on one side and intended to carry a nut (11), the nut retainer (7) comprising at least one lever (13), said lever (13) being mobile between an opened position and a closed position of the chamber (9), the lever (13) being destined to support a nut (11) when being in the closed position.

Description

[0001] 2024P00080DE

[0002] Maintenance tool comprising a nut retainer

[0003] The present disclosure relates to nuclear reactor maintenance equipment, specifically tools for tensioning and detensioning control rod drive mechanism (CRDM) assemblies within an evolutionary power reactor.

[0004] Maintenance activities within nuclear reactors are complex, often requiring the shutdown of the facility and intricate maneuvers to access and service the internal components. These activities are further complicated by the need to minimize radiation exposure for personnel and the spatial constraints of the reactor's interior. Traditional methods for servicing these components involve intricate procedures that are not only time-consuming but also pose a risk of exposure to hazardous conditions.

[0005] Conventional approaches to servicing internal components often rely on a series of manual manipulations and the use of specialized tools to secure and adjust various fasteners. These tools operate effectively within the confined spaces of the reactor and ensure that no parts are misplaced or dropped, as such incidents could lead to significant operational disruptions and potential safety hazards. The industry has recognized the need for improved tools that enhance safety, efficiency, and precision during these maintenance operations.

[0006] Maintenance of control rod drive mechanisms (CRDMs) in power reactors presents a significant challenge due to the close proximity of CRDM assemblies within the reactor's closure head. The CRDM facilitates the movement of control rods, which regulate the nuclear reaction. During maintenance, the tightening and loosening of studs that secure the CRDMs are tasks that require precise execution. Traditional methods for performing these tasks involve manual operations that are time-consuming and expose maintenance personnel to radiation for extended periods. Furthermore, the risk of dropping components such as nuts within the reactor poses a significant contamination threat.

[0007] Existing solutions for CRDM maintenance involve the use of tools that require manual handling of nuts and studs, which can be 2024P00080DE cumbersome and inefficient. These tools often necessitate the removal of surrounding CRDM assemblies to access the target assembly, leading to increased downtime and radiation exposure. Additionally, the manual retention mechanisms used to hold the nuts in place are prone to failure, increasing the risk of losing nuts within the reactor. The complexity of these tools and the precision required for their operation also contribute to the overall challenge of maintaining CRDMs efficiently and safely.

[0008] The present maintenance tool addresses these challenges by providing an automated solution for the carrying of nuts near studs useful for the tensioning and detensioning of said studs on CRDM assemblies.

[0009] The invention relates to a maintenance tool, for example of a control rod drive mechanism of a power reactor, that comprises a carrying ring and a nut retainer supported by the carrying ring and designed to facilitate the handling of nuts during maintenance operations.

[0010] The carrying ring comprises a chamber opened on one side and intended to carry a nut, and the nut retainer comprises at least one lever, said lever being mobile between an opened position and a closed position of the chamber, the lever being destined to support the nut when being in the closed position, allowing for secure and efficient maintenance operations.

[0011] The tool's design ensures homogeneous and simultaneous tensioning of studs, as well as the transport and release of nuts within the tool, thereby minimizing the risk of contamination and reducing maintenance time and radiation exposure.

[0012] According to one aspect of the invention, the lever compri ses a blade with a thickness between 0,5 and 4 mm, preferably between 1 and 2 mm, the blade being destined to support the nut.

[0013] Advantageously, the blade is L-shaped and comprises a recess to avoid a stud entering the supported nut to touch said blade, the blade sliding against the carrying ring when moving between the opened position and the closed position.

[0014] Advantageously, each lever comprises a cam, the nut retainer comprising a mechanism interacting with said cam. 2024P00080DE

[0015] In one embodiment, the mechanism comprises a pi ston, preferably a pneumatic piston, and a spring, said spring exerting a force on the piston aiming to put said piston in a position which aim to put the lever in a closed position.

[0016] In one particular embodiment, the nut retainer comprises a pin and a spring for each lever, the pin being linked to the spring, the pin and the spring exerting a force on the cam of the lever aiming to put said lever in a closed position.

[0017] Advantageously, the maintenance tool comprises an even number of levers, the nut retainer comprising one mechanism for two levers.

[0018] Advantageously, the mechanism is positioned inside the carrying ring.

[0019] In one embodiment, the maintenance tool comprises as many levers as chambers.

[0020] Advantageously, each lever is realized in stainless steel

[0021] The present invention and its advantages will be better understood by studying the detailed description of specific embodiments given by way of non-limiting examples and illustrated by the appended drawings on which:

[0022] Figure 1 is a cross-sectional view of the maintenance tool according to the invention, the maintenance tool being engaged with a CRDM assembly and comprising a lever in a closed position;

[0023] Figure 2 is a bottom view of the maintenance tool of the figure 1 with two levers in the closed position;

[0024] Figure 3 is a bottom view of the CRDM maintenance tool of the figure 1 with two levers in an opened position; and

[0025] Figure 4 is a bottom view of the CRDM maintenance tool of the figure 1 with a lever in an opened position and a lever in a closed position.

[0026] The maintenance tool 1 of a control rod drive mechani sm 3 of a power reactor as illustrated on figure 1 comprises a carrying ring 5 and a nut retainer 7. The carrying ring 5 includes a chamber 9 that is opened on one side and intended to carry a nut 1 1. The dimensions of the chamber 9 are consequently similar to the dimensions of the nut destined to be inserted in said chamber. 2024P00080DE

[0027] The chamber 9 provides a secure location for the nut 1 1 during the maintenance process and more importantly permits to transport the nut 1 1 towards his nominal location, where it will be screwed onto a stud 17, or toward the exterior of the control rod drive mechanism 3. The chamber 9 also ensures that the nut 1 1 is held in proximity to the stud 17 for tensioning and detensioning operations. The carrying ring 5 is designed to accommodate the spatial constraints within the reactor and allows for the uniform and simultaneous tensioning of studs, which is important for the maintenance of the CRDM assemblies. Furthermore, the nut retainer 7 is designed such that when positioned in an opened position, as required during the tightening of the stud 17, a load can be transmitted from a tensioner tool through the nut retainer 7, to the surface of the structure to which the nut is to be secured, maximizing the contact area and reducing stresses and the risk of damages.

[0028] The nut retainer 7 comprises at least one lever 13 , which i s mobile between an opened position and a closed position of the chamber 9. The lever 13 is destined to support a nut 1 1 when being in the closed position. The mobility of the lever 13 between the opened and closed positions facilitates the secure handling of the nut 1 1 , allowing for the transport and release of the nut 1 1 within the maintenance tool 1. The lever 13 ensures that the nut 1 1 is retained during the maintenance operation and can be released with the opened position in a controlled manner, minimizing the risk of contamination within the reactor.

[0029] The lever 13 compri ses a blade 15 with a thickness between 0.5 and 4 mm, preferably between 1 and 2 mm . The blade 15 is destined to support the nut 1 1 .

[0030] The blade 15 is L-shaped and includes a recess 18 to avoid a stud 17 entering the supported nut 1 1 to touch the blade 15. The blade 15 is designed to slide against the carrying ring 5 when moving between the opened position and the closed position. This design of the blade 15 ensures that the stud 17 does not come into contact with the blade 15 , which could potentially damage the stud 17, or the blade 15, or impede the maintenance process.

[0031] The lever 13 is configured to maximise the contact area with the nut 1 1 , securing it against removal, in the closed position whil st prohibiting any contact with the nut 1 1 or the stud 17 when in the opened 2024P00080DE position. It must also not be possible for the lever 13 to contact with the stud 17 when in the closed position. The maximization of the surface contact between the nut 1 1 and the lever 13 holds preferably the nut 1 1 in a strictly horizontal position, promoting ease of removal, whil st having sufficient strength to resist damage or distortion from removal attempts. It reduces the risk that a nut 1 1 may snag or catch.

[0032] Each lever 13 comprises a cam 19, and the nut retainer 7 includes a mechanism 21 destined to interact with the cam 19. For example, the cam is linked to the blade by a rivet 22.

[0033] The mechanism 21 comprises a piston 23 , preferably a pneumati c piston, and a spring 25. The mechanism may comprise a mechanical gear to transport the movement from the piston 23 to the cam 19. The spring 25 exerts a force on the piston 23 aiming to put the piston 23 in a position which aims to put the lever 13 in the closed position. This configuration allows a controlled movement of the lever 13 and ensures that the lever 13 remains in the closed position unless actively moved by the mechanism 21 , in particular by a pneumatic activation of the piston. The use of a pneumatic piston provides a reliable and responsive means of actuating the lever 13. On the figure 1 , the pneumatic alimentation 26 connects a pneumatic tank and the piston 23.

[0034] The nut retainer 7 comprises a pin 27 and a spring (not represented) for each lever 13 , with the pin 27 being linked to the spring. The pin 27 and the spring exert a force on the cam 19 of the lever 13 aiming to put the lever 13 in a closed position unless actively moved in the opened position by the mechanism 21. This design ensures that each lever 13 can be independently opened, allowing for the individual manipulation of each nut 1 1 . The inclusion of a pin 27 and a spring for each lever 13 provides a fail-safe mechanism, ensuring that the lever 13 remains in the closed position in the event of a loss of power or actuation force. An operator can nevertheless open one lever at a time by simply positioning with his hand said lever in the opened position, as seen in figure 4, and without an additional tool . The designed forces operating the lever 13 are precisely balanced such that it is not possible to generate sufficient loads to cause injury to the hand of an operator.

[0035] The CRDM often comprises an even number of nuts to be screwed around studs, for example 10 nuts. The maintenance tool 1 2024P00080DE consequently comprises an even number of levers 13 , for example l a levers, with the nut retainer 7 comprising one mechanism 21 for two levers 13 , as seen in the figures 1 to 4. This arrangement allows for a compact design of the nut retainer 7, optimizing the use of space within the carrying ring 5.

[0036] The mechanism 21 is furthermore positioned inside the carrying ring 5, further contributing to the streamlined design of the maintenance tool 1 and ensuring that the mechanism 21 is protected from the external environment.

[0037] The maintenance tool 1 comprises as many levers 13 as chambers 9, ensuring that each nut 1 1 can be individually supported and manipulated during the maintenance process. This one-to-one correspondence between levers 13 and chambers 9 allows for preci se control over the nuts 1 1 and facilitates the simultaneous or individual tensioning and detensioning of the studs 17.

[0038] Each lever 13 is realized in stainless steel, providing the necessary strength and corrosion resistance required for the harsh environment within a nuclear reactor. The use of stainless steel ensures the durability and longevity of the levers 13 , contributing to the overall reliability of the maintenance tool 1 during CRDM servicing operations.

Claims

2024P00080DECLAIMS1. Maintenance tool (1) comprising a carrying ring (5) and a nut retainer (7) supported by the carrying ring, wherein the carrying ring (5) comprises a chamber (9) opened on one side and intended to carry a nut (11), and wherein the nut retainer (7) comprises at least one lever (13), said lever (13) being mobile between an opened position and a closed position of the chamber (9), the lever (13) being destined to support the nut (11) when being in the closed position.

2. Maintenance tool (1) according to claim 1, wherein said lever (13) comprises a blade (15) with a thickness between 0,5 and 4 mm, preferably between 1 and 2 mm, the blade (15) being destined to support the nut (11).

3. Maintenance tool (1) according to claim 2, wherein the blade (15) is L-shaped and comprises a recess (18) to avoid a stud (17) entering the supported nut (11) to touch said blade (15), the blade (15) sliding against the carrying ring (5) when moving between the opened position and the closed position.

4. Maintenance tool (1) according to any of the preceding claims, wherein said lever (13) comprises a cam (19), the nut retainer (7) comprising a mechanism (21) interacting with said cam (19).

5. Maintenance tool (1) according to claim 4, wherein the mechanism (21) comprises a piston (23), preferably a pneumatic piston, and a spring (25), said spring (25) exerting a force on the piston aiming to put said piston (25) in a position which aim to put the lever (13) in a closed position.

6. Maintenance tool (1) according to claim 4 or 5, wherein the nut retainer (7) comprises a pin (27) and a spring (25) for said lever (13), the pin (27) being linked to the spring (25), the pin (27) and the spring (25) exerting a force on the cam (19) of the lever (13) aiming to put said lever (13) in a closed position.

7. Maintenance tool (1) according to any of the claim 4 to 6, comprising an even number of levers (13), the nut retainer (7) comprising one mechanism (21) for two levers (13).

8. Maintenance tool (1) according to any of the claim 4 to 7, wherein the mechanism (21) is positioned inside the carrying ring (5).2024P00080DE9. Maintenance tool (1) according to any of the preceding claims, comprising as many levers (13) as chambers (9).

10. Maintenance tool (1) according to any of the preceding claims, wherein each lever (13) is realized in stainless steel.

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