Maintenance tool for screwing a nut around a stud

Abstract

This maintenance tool (1) for screwing a nut (3) around a stud (5) protruding from a flange (7) comprises a carrying ring (9) comprising a chamber (11) with an opening (13) on one side, and a gear socket (15) positioned in the chamber (13), the gear socket (15) being intended to fit the shape of the nut (3) carried in the chamber (11) and being mobile along a rotational movement on itself and a translation toward the opening (13).

Description

[0001] 2024P00081 DE

[0002] Maintenance tool for screwing a nut around a stud

[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] More specifically, the present disclosure relates to the screwing of nuts on the adapter nozzle of the control rod drive mechanism in order to ensure a correct sealing of said adapter nozzle.

[0005] 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.

[0006] 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.

[0007] 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 nuts and studs that secure the CRDMs are tasks that require preci se 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 2024P00081 DE dropping components such as nuts within the reactor poses a significant contamination threat.

[0008] Existing solutions for CRDM maintenance involve the use of tools that require manual handling of nuts and studs, which can be 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. It should be noted that a reactor comprises for example between 10 and 200 CRDM. 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.

[0009] The present maintenance tool addresses these challenges by providing an automated solution for the screwing of nuts around studs useful for the tensioning and detensioning of said studs on CRDM assemblies. An advantage of the present invention is to offer a great stroke for screwing a nut around a stud with a particularly compact design.

[0010] The invention relates to a maintenance tool, for example of a control rod drive mechanism of a power reactor, for screwing a nut around a stud protruding from a flange, the maintenance tool comprising a carrying ring comprising a chamber with an opening on one side, and a gear socket positioned in the chamber, the gear socket being intended to fit the shape of the nut carried in the chamber and being mobile along a rotational movement on itself and a translation toward the opening, the rotational movement and the translation being destined to be decorrelated in order to reset the stroke of the gear socket according to the direction of its translation.

[0011] It is understood that the rotational movement and the translation being destined to be decorrelated does not mean that those movements can’t be correlated, for example during a screwing, but said movements have the possibility to be decorrelated.

[0012] The maintenance tool thus permits to screw nuts on studs of a CRDM, the maintenance tool being reusable for all the CRDM of a reactor. 2024P00081 DE

[0013] The translation and the rotational movement are not linked into a fixed helical movement. Thus, a helical movement for screwing can be obtained, as well as only a pure translation in order to reset the stroke of the gear socket and increase the total stroke on which a nut can be screwed, with a great compacity of the maintenance tool . This effect constitutes the center of the invention.

[0014] According to one embodiment, the gear socket comprises an external thread, the maintenance tool comprising a motor and a drive sprocket engaged with the external thread of the gear socket, the motor driving the drive sprocket so that the gear socket rotates on itself.

[0015] Advantageously, the motor i s an electric motor, minimizing the space taken for rotating the gear socket.

[0016] In one embodiment, the maintenance tool comprises an abutment ring forming the opening of the chamber and preventing the gear socket to disengage with the drive sprocket.

[0017] According to one aspect of the invention, the maintenance tool comprises a spring positioned in the chamber, the spring exerting a force on the gear socket and / or the nut aiming to push said nut out of the chamber toward the opening.

[0018] It also permits to maintain the engagement of the gear socket on the nut throughout the screwing process.

[0019] In one particular embodiment, the maintenance tool comprises a support cylinder protruding from the carrying ring toward the flange and destined to fix a distance between said carrying ring and the flange.

[0020] Advantageously, the support cylinder is an electric support cylinder, minimizing the space taken for fixing the distance between the carrying ring and the flange.

[0021] Advantageously, the stroke of the gear socket is inferior to half of the length of the nut.

[0022] The length of the nut is understood as the axial dimension of the nut. It thus permits the maintenance tool to be manufactured with a very compact design and still with a high stroke of the gear socket as it can be reset.

[0023] Preferably, the maintenance tool comprises a 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. 2024P00081 DE

[0024] Advantageously, the carrying ring comprises at least two chambers and gear sockets, preferably 10 chambers and gear sockets.

[0025] The invention also relates to a method to use the maintenance tool as described above, the method comprising the following steps :

[0026] - Approaching the maintenance tool carrying a nut fitted in the gear socket from the flange and the stud in order for the nut and the stud to touch each other;

[0027] - Setting in motion the gear socket with a helical movement toward the opening in order to screw the nut around the stud;

[0028] - Replacing the nut entirely in the chamber without unscrewing said nut from the stud by approaching the carrying ring from the flange;

[0029] - Repeating the last two steps of setting in motion the gear socket and replacing the nut in the chamber until the nut abuts against the flange.

[0030] 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:

[0031] Figure 1 to 6 are cross-sectional and schematical views of the maintenance tool according to the invention, the maintenance tool being shown at different stages of the screwing of a nut around a stud; and

[0032] Figure 7 is a schematic representation of the method to use the maintenance tool according to the invention.

[0033] The maintenance tool 1 of a control rod drive mechanism of a power reactor is designed for screwing a nut 3 around a stud 5 protruding from a flange 7.

[0034] The maintenance tool 1 comprises a carrying ring 9 which includes a chamber 1 1 with an opening 13 on one side. The chamber 1 1 is designed to house the nut 3 during the maintenance operation.

[0035] In one particular embodiment, the maintenance tool 1 comprises more than two chambers 1 1 , for example ten chambers 1 1 , housing as many nuts 3 to be screwed on as many studs 5 of the flange 7. Preferably, all nuts 3 are to be screwed all together on the same time.

[0036] A gear socket 15 is positioned in the chamber 1 1 and is intended to fit the shape of the nut 3 carried in the chamber 1 1. For example, the 2024P00081 DE nut is a hexagonal nut, the gear socket 15 thus has an inner hexagonal section designed to fit said nut 3. When a nut 3 is inserted in the gear socket 15, they are considered as solidly connected to each other, due in particular to the force of the spring 23 described below.

[0037] The gear socket 15 is mobile along a rotational movement on itself and a translation toward the opening 13. In other words, the gear socket 15 is mobile along a helical movement facilitating the engagement and disengagement of the nut 3 with the stud 5.

[0038] A helical movement is the sum of a rotational movement and of a translation. Here, the translation and the rotational movement are not linked into a fixed helical movement, they are two di stinct movements. A helical movement for screwing can be obtained when adding the rotational movement and the translation, but a pure translation is also possible in order to reset the stroke of the gear socket and increase the total stroke on which a nut can be screwed. A better description of this advantage will be made during the description of figure 7.

[0039] The gear socket 15 also comprises an external thread 17, which interacts with a drive sprocket 19, more particularly which rotates on itself under the influence of the drive sprocket 19. For example, each the gear socket 15 and the drive sprocket 19 have teeth that are respectively engaged to ensure the rotation, and also forming grooves allowing a transversal movement along said grooves, the gear socket 15 being able to slide in translation against the drive sprocket 19.

[0040] The translation is favored by the tapping and thread of the nut 3 and the stud 5, the screwing of the nut 3 around the stud 5 forcing the nut 3 and the gear socket 15 to translate toward the opening 13.

[0041] The maintenance tool 1 comprises a motor 20, linked to the drive sprocket 19 with a mechanical gear. The motor 20 drives the drive sprocket 19 so that the gear socket 15 rotates on itself, enabling the screwing or unscrewing of the nut 3.

[0042] The motor 20 is an electric motor, providing the necessary power and control for the precise movement of the gear socket 15. It may present also an advantage for its compacity, the maintenance tool being used in a constrained environment.

[0043] An abutment ring 21 forms the opening 13 of the chamber 1 1. The abutment ring 21 is positioned on the way of the gear socket 15 so 2024P00081 DE that said abutment ring 21 prevents the gear socket 15 from dropping when there is no nut 3 in the carrying ring 9. The abutment ring 21 also prevents the gear socket 15 from disengaging with the drive sprocket 19.

[0044] In other words, the gear sockets 15 is mobile in translation compared to the drive sprocket 19. However, the gear sockets 15 is always engaged with said drive sprocket 19 and the abutment ring ensures that the gear socket 15 remains engaged during the maintenance operation, providing stability and reliability.

[0045] A spring 23 is positioned in the chamber 1 1 , exerting a force on the gear socket 15 and / or the nut 3 aiming to push said nut 3 out of the chamber 1 1 toward the opening 13. This feature assists in the engagement of the nut 3 with the stud 5 and ensures that the nut 3 is readily available for screwing onto the stud 5. The spring 23 also helps to initiate the translation movement of the gear socket 15 and nut 3.

[0046] The maintenance tool 1 also comprises a support cylinder 25 protruding from the carrying ring 9 toward the flange 7 on which it takes support. The support cylinder 25 i s destined to fix a distance between said carrying ring 9 and the flange 7. The support cylinder 25 is an electric support cylinder, providing precise control over the distance maintained between the carrying ring 9 and the flange 7 during the maintenance operation. For example, the maintenance tool 1 comprises three support cylinders 25 in order to have an isostatic support between the carrying ring and the flange.

[0047] A lever 27 is included in the maintenance tool 1 , being mobile between an opened position and a closed position of the chamber 1 1. The lever 27 is destined to support the nut 3 when being in the closed position, ensuring that the nut 3 is securely held in place during the maintenance process and especially when the nut 3 is carried near the stud 5.

[0048] The carrying ring 9 comprises at least two chambers 1 1 and gear sockets 15, preferably 10 chambers 1 1 and gear sockets 15, allowing for the simultaneous screwing of multiple studs 5 and nuts 3. This feature significantly enhances the efficiency of the maintenance operation by allowing multiple nuts 3 to be screwed or unscrewed concurrently. 2024P00081 DE

[0049] Also, the simultaneous screwing of all nuts 3 is preferably wanted, in order to bring the carrying ring 9 and the flange 7 closer, by reducing the length of the support cylinders 25 simultaneously.

[0050] Additionally, the maintenance tool 1 comprises a position sensor destined to measure the axial position of the gear socket 15 and the nut 3. More precisely, the position sensor monitors the nut 3 altitude in regard to the flange 7, via a measure on the gear socket 15.

[0051] The maintenance tool 1 may also comprise a distance sensor monitoring the carrying ring altitude in regard to the flange 7.

[0052] The figure 7 illustrate the method to use the maintenance tool l according to the invention. Reference to the figure 1 to 6 will me made at each step of the method.

[0053] The method to use the maintenance tool 1 involves a first step E l of approaching the maintenance tool 1 carrying a nut 3 fitted in the gear socket 15 from the flange 7 and the stud 5, so that the nut 3 and the stud 5 touch each other. This step E l is illustrated by the figure 1. The illustrated stud 5 comprise two parts of different diameters. The part on which the nut 3 is to be screwed is the below part, the upper part having a smaller diameter.

[0054] In a second step E2, the gear socket 15 is set in motion with a helical movement toward the opening 13 in order to screw the nut 3 around the stud 5. This step E2 ends with the gear socket 15 hitting the abutment ring 21 and is illustrated by the figure 2. As previously described, the helical movement is a combination of a rotational movement given by the drive sprocket 19 and the forced translation induced by the thread along with the spring 23.

[0055] Then, during a step E3 , the nut 3 is replaced entirely in the chamber 1 1 without unscrewing said nut 3 from the stud 5 by approaching the carrying ring 9 from the flange 7. This step E3 is illustrated by the figure 3. Here, the length of the support cylinder 25 is reduced and the carrying ring 9 is getting closer to the flange 7. The drive sprocket 19 and the gear socket 15 simply glide on one another teeth. This step E3 permits to enhance the total stroke for the screwing of the nut 3. 2024P00081 DE

[0056] These steps E2 and E3 of setting in motion the gear socket 15 and replacing the nut 3 in the chamber 1 1 are repeated until the nut 3 abuts against the flange 7.

[0057] In particular, the figure 4 illustrates a repetition of the step E2 and the figure 5 is a repetition of the step E3.

[0058] The figure 6 illustrates a repetition of the step E2 and the abutment of the nut 3 against the flange 7. Th abutment can be detected by the position sensor of the gear socket 15, measuring an absence of movement during a step E4. The stud 5 is secured by the nut 3. The stud can be tensioned by another specific tensioning device while being secured by the nut 3.

Claims

2024P00081DECLAIMS1. Maintenance tool (1) for screwing a nut (3) around a stud (5) protruding from a flange (7), the maintenance tool (1) comprising a carrying ring (9) comprising a chamber (11) with an opening (13) on one side, and a gear socket (15) positioned in the chamber (13), the gear socket (15) being intended to fit the shape of the nut (3) carried in the chamber (11) and being mobile along a rotational movement on itself and a translation toward the opening (13), the rotational movement and the translation being destined to be decorrelated in order to reset the stroke of the gear socket (15) according to the direction of its translation.

2. Maintenance tool (1) according to claim 1, wherein the gear socket (15) comprises an external thread (17), the maintenance tool (1) comprising a motor (20) and a drive sprocket (19) engaged with the external thread (17) of the gear socket (15), the motor (20) driving the drive sprocket (19) so that the gear socket (15) rotates on itself.

3. Maintenance tool (1) according to claim 2, wherein the motor (20) is an electric motor.

4. Maintenance tool (1) according to any of the claims 2 and 3, comprising an abutment ring (21) forming the opening (13) of the chamber (11) and preventing the gear socket (15) to disengage with the drive sprocket (19) and to drop when there is no nut (3) in the carrying ring (9).

5. Maintenance tool (1) according to any of the preceding claims, comprising a spring (23) positioned in the chamber (11), the spring (23) exerting a force on the gear socket (15) and / or the nut (3) aiming to push said nut (3) out of the chamber (11) toward the opening (13).

6. Maintenance tool (1) according to any of the preceding claims, comprising a support cylinder (25) protruding from the carrying ring (9) toward the flange (7) and destined to fix a distance between said carrying ring (9) and the flange (7).

7. Maintenance tool (1) according to any of the preceding claims, wherein the stroke of the gear socket (15) is inferior to half of the length of the nut (3).2024P00081DE8. Maintenance tool (1) according to any of the preceding claims, comprising a lever (27) being mobile between an opened position and a closed position of the chamber (11), the lever (27) being destined to support the nut (3) when being in the closed position.

9. Maintenance tool (1) according to, wherein the carrying ring (9) comprises at least two chambers (11) and gear sockets (15), preferably 10 chambers (11) and gear sockets (15).

10. Method to use the maintenance tool (1) according to any of the preceding claims, comprising the following steps:Approaching (step El) the maintenance tool (1) carrying a nut (3) fitted in the gear socket (15) from the flange (7) and the stud (5) in order for the nut (3) and the stud (5) to touch each other;Setting in motion (step E2) the gear socket (15) with a helical movement toward the opening in order to screw the nut (3) around the stud (5);- Replacing (step E3) the nut (3) entirely in the chamber (11) without unscrewing said nut (3) from the stud (5) by approaching the carrying ring (9) from the flange (7);- Repeating the last two steps (E2; E3) of setting in motion the gear socket (15) and replacing the nut (3) in the chamber (11) until the nut (3) abuts (step E4) against the flange (7).

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