Method and kit to control the applied torque value on a nut screwed around a stud

Abstract

This method to control a nut screwed around a stud by a gear socket under the action of a motor comprises the following steps : - Establishing a correlation table (step E1) between different motor supply current values and a torque applied by the gear socket on a torque sensor fitted in the gear socket; - Removing of the torque sensor from the gear socket and placing the nut instead (step E2); - Screwing (step E3) the nut around the stud; - Comparing the motor supply current value with the motor supply current values stored in the established correlation table (step E4); - Extract the torque (step E5) once a match is found during the comparison step (E4).

Description

[0001] 2024P00082DE

[0002] Method and kit to control the applied torque value on a nut screwed 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] Even more specifically, the present disclosure relates to systems and methods for controlling parameters, for example a torque, during the screwing and unscrewing of nuts.

[0006] 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.

[0007] 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.

[0008] 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 2024P00082DE 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.

[0009] 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.

[0010] 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.

[0011] Furthermore, ensuring the integrity of threaded connections requires precise application of force to avoid damage to threads and to ensure uniform tightness of the nuts around the studs. Traditional methods for controlling this force involve indirect measurements that might not provide an accurate representation of the actual force applied. These indirect methods can introduce variables that affect the precision of the force measurement, leading to potential inconsistencies in the assembly process.

[0012] Techniques currently employed to monitor and control the application of force during assembly operations strive for consistency in securing components. Despite these efforts, there remains a risk of applying inappropriate levels of force, which can result in uneven distribution of stress and potential compromise in the structural integrity of the assembly. The industry is in pursuit of improved monitoring and control methods to ensure the reliability and accuracy of these operations. 2024P00082DE

[0013] The invention relates to a method to control a nut rotation parameters screwed around a stud protruding from a flange by a maintenance tool, for example of a control rod drive mechanism of a power reactor, said 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 helical movement toward the opening under the action of a DC motor.

[0014] The method comprises the following steps :

[0015] - Establishing upstream a correlation table between different motor supply current values and a torque applied by the gear socket on a torque sensor fitted in the gear socket;

[0016] - Removing of the torque sensor from the gear socket and placing the nut fitted in the gear socket instead;

[0017] - Screwing the nut around the stud with the gear socket moving along a helical movement;

[0018] - Comparing, during the screwing, the motor supply current value with the motor supply current values stored in the established correlation table;

[0019] - Extracting the torque applied by the gear socket on the nut once a match is found during the comparison step.

[0020] 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. In the same time, the method is implemented to know exactly which torque is applied on the nut by the motor and the gear socket.

[0021] Furthermore, a correlation table is established for every gear socket of the maintenance tool, the measure being thus individualized and specific to the particularities of each gear socket.

[0022] This method minimizes the risk of error of the extracted torque, maximizes the lifetime of the threads of the nuts and studs, and minimizes the difference of residual load from one stud to another, which guarantee a homogeneous tightening.

[0023] Advantageously, the method comprises a step of stopping the screwing if the torque applied by the gear socket on the nut i s equal or superior to a predefined torque.

[0024] This permits to avoid damaging the threads of the nut or the stud. 2024P00082DE

[0025] In one aspect of the invention, the torque sensor is destined to measure a static and / or dynamic torque, the torque sensor comprising a rotary torque sensor or / and a static reaction torque sensor.

[0026] In one particular embodiment, the maintenance tool comprises at least two chambers and gear sockets, preferably 10 chambers and gear sockets, the method comprising the step of establishing upstream a correlation table for each gear socket of the maintenance tool independently.

[0027] Advantageously, the method comprises a step of measuring the altitude of the nut in regard to the flange during the step of screwing.

[0028] In one embodiment, the method comprises a step of emitting an alarm signal if the torque applied by the gear socket on the nut is equal or superior to a predefined torque and the altitude of the nut in regard to the flange do not match a predefined distance.

[0029] Obviously, the predefined torque can be different in respect with the nut altitude.

[0030] The present invention al so relates to a kit for implementing the method previously defined, comprising 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 helical movement toward the opening under the action of a DC motor, the kit al so compri sing a torque sensor destined to be fitted in the gear socket.

[0031] In one embodiment, the kit comprises a control unit including a memory unit destined to store the correlation table, the control unit being destined to implement the steps of the method.

[0032] Advantageously, the torque sensor comprises a rotary torque sensor or / and a static reaction torque sensor.

[0033] In one particular embodiment, the maintenance tool comprises a distance sensor destined to give back the altitude of the nut in regard to the flange.

[0034] The present invention and its advantages will be better understood by studying the detailed description of specific embodiments 2024P00082DE given by way of non-limiting examples and illustrated by the appended drawings on which:

[0035] Figure 1 is a cross-sectional view of the maintenance tool with which a nut is screwed around a stud and with which the present invention is implemented in order to know the torque applied to said nut;

[0036] Figure 2 is a schematic representation of the method to control a nut rotation parameters according to the invention; and

[0037] Figure 3 is a schematic representation of the kit for implementing the method according to the invention.

[0038] 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.

[0039] 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.

[0040] In one particular embodiment, the maintenance tool 1 comprises 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.

[0041] 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 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. In a preferred embodiment, the nut has a shape similar to gear wheels in a clutch to ease the connection / insertion as soon as the socket 15 turns just a little.

[0042] 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.

[0043] A helical movement is the sum of a rotational movement and of a translation. Here, the translation and the rotational movement are lot linked into a fixed helical movement. A helical movement for screwing can be obtained when adding the rotational movement and the 2024P00082DE 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.

[0044] 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.

[0045] 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.

[0046] The maintenance tool 1 comprises a motor 20, linked to the drive sprocket 19 with a mechanical gear 22. 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.

[0047] 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.

[0048] 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 that said abutment ring 21 prevents the gear socket 15 from dropping when there is no nut 3 in the carrying ring 9, and so prevents the gear socket 15 from disengaging with the drive sprocket 19.

[0049] On the opposite, when the nut 3 is carried by the carrying ring 9, if the nut 3 rotation is not stopped, at some point, when the gear socket 15 hits the abutment ring 21 , the gear socket 15 may be disengaged from the nut 3. In such case, the maintenance tool 1 «looses» the control of the nut 3. This is why each gear socket 15 and / or nut 3 have an altitude measurement with a distant sensor.

[0050] 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 2024P00082DE ensures that the gear socket 15 remains engaged during the maintenance operation, providing stability and reliability.

[0051] 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.

[0052] 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. Alternatively, the maintenance tool 1 comprises at least four support cylinders 25, the support being hyperstatic.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Additionally, the maintenance tool 1 comprises a position sensor destined to measure the axial position of the gear socket 15, and optionally of the nut 3. 2024P00082DE

[0057] The figure 2 illustrate the method to control the nut 3 rotation parameters screwed around the stud 5 protruding from the flange 7 by the maintenance tool 1 of the control rod drive mechanism of the power reactor.

[0058] As previously mentioned, the gear socket 15 is mobile along a helical movement toward the opening under the action of the motor 20. The motor 20 is a DC motor 20, the intensity of the current being proportional to the power of said motor. For example, the voltage i s 24 Volts.

[0059] The method comprises a first step El realized upstream, in other words before using the maintenance tool on the nut 3. During this step, generally performed outside of the power reactor area, a torque sensor 29 is inserted in the chamber 1 1 and fitted in the gear socket 15 so that said gear socket 15 applies a torque on the torque sensor 29. The kit 3 1 for implementing the present method is illustrated on the figure 3 , said kit 3 1 comprising the maintenance tool 1 and the torque sensor 29.

[0060] In one aspect of the invention, the torque sensor 29 is destined to measure a static and / or dynamic torque, the torque sensor 29 comprising respectively a static reaction torque sensor or / and a rotary torque sensor.

[0061] This first step E l is the establishment of a correlation table between different motor supply current values of the motor 20 and a torque applied by the gear socket 15 on the torque sensor 29 fitted in the gear socket 15. Thus, for each different motor supply current values, for exempla in mA, corresponds a torque value, for example in N.m, measured by the torque sensor 29.

[0062] In one embodiment, the kit 3 1 also comprises a control unit 33 including a memory unit 35 destined to store the correlation table once said correlation table is established, the control unit 33 being destined to implement the steps of the method and being linked to the motor 20.

[0063] Then, a step E2 of removing the torque sensor 29 from the gear socket 15 is performed, the nut 3 being placed fitted in the gear socket 15 instead. The maintenance tool 1 is ready to use with the control rod drive mechanism and i s placed near the stud 5. 2024P00082DE

[0064] In another embodiment, the step E l and E2 are replaced by a step of establishment of a correlation table with a mathematical formula making a motor supply current value correspond to a torque value.

[0065] The method then comprises a step E3 of screwing the nut 3 around the stud 5 with the gear socket 15 moving along a helical movement.

[0066] During the screwing, a step E4 of comparing the effective motor supply current value with the motor supply current values stored in the established correlation table is performed.

[0067] Then, once a match is found during the comparison step E4, the corresponding torque value applied by the gear socket 15 on the nut 3 is extracted in a step E5. This value may be displayed on a screen.

[0068] Advantageously, the method comprises a step E6 of stopping the screwing if the torque value applied by the gear socket 15 on the nut 3 is equal or superior to a predefined torque value.

[0069] Thus, if the nut 3 is screwed under a too high torque value, the screwing stops, minimizing the impact of the screwing of the nut 3 on the tightening of the stud 5, the stud 5 being tightened precisely by another module.

[0070] Advantageously, and as previously described, the maintenance tool 1 comprises at least two chambers 1 1 and gear sockets 15, preferably 10 chambers and gear sockets, for the screwing of the same amount of nuts 3. The method comprises the step E l of establishing upstream a correlation table for each gear socket 15 of the maintenance tool 1 independently.

[0071] Thus, each particularity of each gear socket 15, and generally each particularity of the mechanical chain between the motor 20 and the gear socket 15, is taken into account in order to extract the most precise torque value. A correlation table is established for each gear socket 15.

[0072] This can guarantee the tightening homogeneity amongst the studs 5, as we know that a torque difference of a few N.m can impact the stud elongation by more than 2%.

[0073] Advantageously, the method comprises a step E7 of measuring the altitude of the nut 3 in regard to the flange during the step E3 of screwing. The maintenance tool 1 comprises a distance sensor destined to give back the altitude of the nut 3 in regard to the flange 7. In one 2024P00082DE particular embodiment, the distance sensor is the position sensor destined to measure the axial position of the gear socket 15.

[0074] Advantageously, the method comprises a step E8 of emitting an alarm signal if the torque value applied by the gear socket 15 on the nut 3 is equal or superior to a predefined torque value and the altitude of the nut 3 in regard to the flange 7 do not match a predefined distance. The alarm signal is thus emitted if the nut 3 finishes to be screwed in a wrong position.

Claims

2024P00082DECLAIMS1. Method to control a nut (3) rotation parameters screwed around a stud (5) protruding from a flange (7) by a maintenance tool ( 1 ), said maintenance tool ( 1 ) comprising a carrying ring (9) comprising a chamber ( 1 1 ) with an opening ( 13) on one side, and a gear socket ( 15) positioned in the chamber ( 1 1 ), the gear socket ( 15) being intended to fit the shape of the nut (3) carried in the chamber ( 1 1 ) and being mobile along a helical movement toward the opening ( 13) under the action of a DC motor (20), the method comprising the following steps :- Establishing upstream a correlation table (step E l ) between different motor supply current values and a torque applied by the gear socket ( 15) on a torque sensor (29) fitted in the gear socket ( 15);- Removing of the torque sensor (29) from the gear socket ( 15) and placing the nut (3) fitted in the gear socket ( 15) instead (step E2);Screwing (step E3) the nut (3) around the stud (5) with the gear socket ( 15) moving along a helical movement;Comparing, during the screwing, the motor supply current value with the motor supply current values stored in the established correlation table (step E4);- Extracting the torque (step E5) applied by the gear socket ( 15) on the nut (3) once a match is found during the comparison step (E4).

2. Method according to claim 1 , comprising a step (E6) of stopping the screwing if the torque applied by the gear socket ( 15) on the nut (3) is equal or superior to a predefined torque.

3. Method according to any of the claims 1 and 2, wherein the torque sensor (29) is destined to measure a static and / or dynamic torque, the torque sensor (29) comprising a rotary torque sensor or / and a static reaction torque sensor.

4. Method according to any of the preceding claims, wherein the maintenance tool ( 1 ) comprises at least two chambers ( 1 1 ) and gear sockets ( 15), preferably 10 chambers ( 1 1 ) and gear sockets ( 15), the2024P00082DE method comprising the step (E l ) of establishing upstream a correlation table for each gear socket ( 15) of the maintenance tool ( 1 ) independently.

5. Method according to any of the preceding claims, comprising a step (E7) of measuring the altitude of the nut (3) in regard to the flange (7) during the step (E3) of screwing.

6. Method according to claim 5, wherein the method comprises a step (E8) of emitting an alarm signal if the torque applied by the gear socket ( 15) on the nut (3) is equal or superior to a predefined torque and the altitude of the nut (3) in regard to the flange (7) do not match a predefined distance.

7. Kit (3 1 ) for implementing the method according to any of the preceding claims, comprising a 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 ( 1 1 ) with an opening ( 13) on one side, and a gear socket ( 15) positioned in the chamber ( 1 1 ), the gear socket ( 15) being intended to fit the shape of the nut (3) carried in the chamber ( 1 1 ) and being mobile along a helical movement toward the opening ( 13) under the action of a DC motor (20), the kit (3 1 ) also comprising a torque sensor (29) destined to be fitted in the gear socket ( 15).

8. Kit (3 1 ) according to claim 7, comprising a control unit (33 ) including a memory unit (35) destined to store the correlation table, the control unit (33) being destined to implement the steps of the method.

9. Kit (3 1 ) according to any of the claims 7 and 8, wherein the torque sensor (29) comprises a rotary torque sensor or / and a static reaction torque sensor.

10. Kit (3 1 ) according to any of the claims 7 to 9, wherein the maintenance tool ( 1 ) comprises a distance sensor destined to give back the altitude of the nut in regard to the flange.

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