Nuclear reactor pressure vessel bolt strain detection apparatus for detecting torsional stress

Abstract

The application relates to a nuclear reactor pressure vessel bolt strain detection device for detecting torsional stress, comprising a probe light source configured to provide incident light; a first strain beam fixedly sleeved on the outside of a bolt nut and having one end limited by a nuclear reactor pressure vessel; a first optical fiber sensor arranged in the first strain beam, and having an optical fiber line arranged at least partially in parallel with the outer contour of the bolt nut; the two ends of the optical fiber line sensing part of the first optical fiber sensor are fixedly sealed to the first strain beam through high-temperature-resistant materials; the first optical fiber sensor is configured to receive the incident light and transmit reflected light to a spectrum detection device; the spectrum detection device is configured to receive the light signal; and a strain calculation electronic device is configured to determine the torsional strain degree of the bolt according to the difference between the reflected light of the first optical fiber sensor obtained by the spectrum detection device before and after the torsional strain of the bolt nut. The device realizes real-time monitoring of the decoupling of the bolt torsional strain and shear strain through double optical fiber sensor differential measurement and a multiple sealing structure, and solves the problems of the prior art, such as the inability to simultaneously and accurately measure torsional and shear stress, poor radiation resistance and insufficient sealing reliability.

Description

Technical Field

[0001] This application belongs to the field of physical sensing and measurement technology, and in particular relates to a strain detection device for bolts of nuclear reactor pressure vessels used to detect torsional stress. Background Technology

[0002] The reactor pressure vessel (RPV) is one of the most critical pieces of equipment in a nuclear power plant reactor system. Its main function is to contain the reactor core and coolant, and to maintain the reactor's safe operation under extreme conditions. The reactor pressure vessel bolts (especially the main top cover bolts) are directly related to the reactor's safe sealing and structural integrity, therefore, extremely stringent requirements are placed on their materials, manufacturing, inspection, and installation. Reactor pressure vessel bolts are nuclear safety grade (Level 1) critical fasteners, with requirements far exceeding those of conventional industrial bolts. Materials must simultaneously meet requirements for high strength, high toughness, resistance to radiation embrittlement, and resistance to stress corrosion. Manufacturing requires full-process quality control and rigorous non-destructive testing. Installation requires precise control of the uniformity and consistency of the preload to ensure the integrity and sealing of the pressure boundary throughout the reactor's entire lifespan.

[0003] In terms of operational characteristics, RPV needs to possess the following key properties: resistance to high temperature and high pressure, typically operating at temperatures above 300℃ and pressures above 15MPa; resistance to neutron irradiation embrittlement, as materials gradually become embrittled due to long-term exposure to neutron radiation, therefore RPV steel must undergo special treatment to slow down this process; sealing and structural integrity, the RPV's sealing system must ensure no coolant leakage while maintaining structural stability under extreme conditions; maintainability and monitorability.

[0004] However, in existing technologies, the main bolts of the top cover of nuclear reactor pressure vessels are often measured beforehand and inspected afterward, lacking effective in-service measurement methods. Furthermore, existing inspection methods struggle to monitor the dynamic changes in torsional and shear stresses in real time and place stringent requirements on the bolt surface condition. There is a lack of an online inspection device capable of simultaneously achieving decoupled measurement of torsional and shear strains, resistant to strong radiation, high temperatures, and with reliable sealing. Therefore, a novel inspection solution based on fiber optic sensing technology is urgently needed to address these technical challenges. Summary of the Invention

[0005] This application provides a strain testing device for bolts of a nuclear reactor pressure vessel used to detect torsional stress, which solves the technical problems existing in the prior art.

[0006] In a first aspect, embodiments of this application provide a strain testing device for bolts of a nuclear reactor pressure vessel used to detect torsional stress, comprising: The detection light source is configured to provide incident light; The first strain beam is fixedly sleeved on the outside of the bolt and nut, and one end of it is limited by the nuclear reactor pressure vessel; A first fiber optic sensor is disposed inside the first strain beam. Its fiber optic line is at least partially parallel to the outer contour of the bolt and nut. Both ends of the sensing part of the first fiber optic line are sealed and fixed to the first strain beam by a high-temperature resistant material. The first fiber optic sensor is configured to receive incident light and transmit reflected light to the spectral detection device. The spectral detection equipment is configured to receive optical signals; The strain calculation electronic device is configured to determine the degree of torsional strain of the bolt based on the difference in reflected light from the fiber optic sensor obtained by the spectral detection device before and after the bolt and nut torsional strain.

[0007] A first optical fiber through hole is formed on the first strain beam, and the optical fiber of the first optical fiber sensor passes through the first optical fiber through hole. Its optical fiber sensing part is set in the first optical fiber through hole, and both ends are sealed and fixed to the optical fiber through hole. Preferably, the first strain beam includes a strain portion that is fixedly engaged with the bolt and nut and an installation portion integrally formed with the strain portion. One end of the installation portion is limited by the nuclear reactor pressure vessel and is provided with the first optical fiber through hole. Preferably, the first optical fiber through-hole is partially parallel to the outer contour of the bolt and nut; preferably, when the bolt is a hexagonal bolt, the first optical fiber through-hole is parallel to at least one side of the outer contour of the hexagonal bolt and nut.

[0008] The device further includes a second optical fiber sensor, wherein the optical fiber extension direction of the second optical fiber sensor is perpendicular to the optical fiber extension direction of the first optical fiber sensor. Preferably, the device further includes an optical fiber connector, through which the optical fiber of the first optical fiber sensor enters the first optical fiber through-hole, and its sensing part is disposed in the first optical fiber through-hole. Preferably, the device further includes a second strain beam disposed within a sealed housing. The sealed housing is fixedly sealed to an optical fiber connector partially embedded in the bolt body. The optical fiber of the second optical fiber sensor enters the sealed housing through the optical fiber connector, and its sensing part is located within the second optical fiber through-hole opened in the second strain beam, with both ends sealed and fixed to the second optical fiber through-hole. The second optical fiber sensor is configured to receive incident light and transmit reflected light to the spectral detection device. Preferably, both the second optical fiber through-hole and the first optical fiber through-hole are provided with a first sealing position at the inlet and a second sealing position at the outlet; Preferably, the optical fiber lines of the first and second optical fiber sensors are radiation-resistant quartz optical fiber lines. Preferably, the optical fibers of the first and second optical fiber sensors are metal-coated quartz optical fibers. Preferably, the optical fiber metal coating of the first and second optical fiber sensors is either a nickel coating or a gold coating.

[0009] In a preferred embodiment, when the fiber optic sensor is located in the bolt body and the fiber optic line is in the first sealing position, it is sealed by gold-tin eutectic brazing and then sealed a second time with high-temperature resistant adhesive. Preferably, when the fiber optic sensor is located in the bolt body and the fiber optic line is in the second sealing position, it is sealed by gold-tin eutectic brazing and then sealed a second time with high-temperature resistant adhesive. Preferably, the solder used for the gold-tin eutectic brazing seal is Au80Sn20 gold-tin eutectic solder; Preferably, the high-temperature resistant adhesive is one of silicone adhesive, polyimide adhesive, or epoxy adhesive; Preferably, the high-temperature resistant adhesive is selected from adhesives with a temperature resistance range of 400°C or higher.

[0010] In a preferred embodiment, the detection light source and the spectral detection device are disposed outside the bolt body; Preferably, the second strain beam is disposed between the two second fiber optic sensors, and the strain calculation electronic device determines the degree of shear strain of the bolt body based on the difference in reflected light between the two second fiber optic sensors obtained by the spectral detection device. Preferably, the device further includes an optical fiber connector partially embedded in the bolt body and a sealed housing fixedly sealed with the optical fiber connector, and the optical fiber lines of the two second optical fiber sensors enter the sealed housing through the optical fiber connector; Preferably, the sealed housing is filled with inert gas; Preferably, the inert gas is selected from one or more of helium, argon, nitrogen, neon, and krypton.

[0011] In a preferred embodiment, the second strain beam is fixedly installed inside the sealed housing. At least two second optical fiber through holes are opened on the second strain beam. The optical fibers of the two second optical fiber sensors are arranged opposite each other on both sides of the second strain beam. After passing through the optical fiber connector, the optical fibers of the two second optical fiber sensors enter the second optical fiber through holes in the sealed housing respectively and are sealed and fixed with the second optical fiber through holes.

[0012] In a preferred embodiment, the sensing portion of the two second fiber optic sensors is located at the part where the fiber optic lines of the two second fiber optic sensors enter the second strain beam. Preferably, the optical fibers of the two second optical fiber sensors terminate at the lower end face of the second strain beam after entering the second strain beam; Preferably, the sensing parts of the two second fiber optic sensors are at the same height level.

[0013] In a preferred embodiment, a first gap is provided between the lower end face of the second strain beam and the upper end face of the gravity pendulum, and the distance between the optical fiber lines of the two second optical fiber sensors and the lower end face of the second strain beam after entering the second strain beam is greater than or equal to the first gap. Preferably, the suspension connection between the gravity pendulum and the second strain beam is located at the center of the lower end face of the second strain beam.

[0014] In a preferred embodiment, the sealed shell is a blind end at the lower end of the gravity pendulum, and the cavity of the blind end is filled with inert gas. Preferably, the sealed housing is provided with a sealing cover at the lower end of the gravity pendulum, the sealing cover is filled with inert gas, and the lower end of the gravity pendulum is free.

[0015] In a preferred embodiment, the upper end of the second strain beam is fixed to the optical fiber connector; Preferably, the side of the second strain beam is in clearance fit with the sealed shell; Preferably, the center of the upper end face of the gravity pendulum and the center of the lower end face of the second strain beam are located on the axis of the sealed shell, and the area of ​​the upper end face of the gravity pendulum is less than or equal to the area of ​​the lower end face of the second strain beam. Preferably, the upper end face of the gravity pendulum and the lower end face of the second strain beam are concentric circles when projected onto the lower end face of the second strain beam, and the area of ​​the upper end face of the gravity pendulum is smaller than the area of ​​the lower end face of the second strain beam.

[0016] In a preferred embodiment, the device further includes a third optical fiber sensor, wherein the optical fibers of the first optical fiber sensor, the second optical fiber sensor, and the third optical fiber sensor extend along the axis of the sealed housing and are uniformly distributed circumferentially according to the axis of the sealed housing.

[0017] In a preferred embodiment, the device further includes an optical fiber coupler configured to transmit the detection light emitted by the detection light source to the optical fiber lines of the two second optical fiber sensors, and to transmit the reflected light from the optical fiber lines to the spectral detection device.

[0018] In a preferred embodiment, the strain calculation electronic device is an electronic device equipped with a strain calculation module. Preferably, the fiber optic coupler is an optical circulator.

[0019] This application's technical solution utilizes dual-fiber sensor differential measurement and a multi-layer sealing structure to achieve decoupled real-time monitoring of bolt torsional strain and shear strain, solving the problems of existing technologies that cannot simultaneously and accurately measure torsional and shear stresses, have poor radiation resistance, and insufficient sealing reliability. Through the cooperation of the first fiber optic sensor and the first strain beam, the torsional strain of the bolt and nut is accurately sensed; through the cooperation of the second fiber optic sensor and the second strain beam, differential measurement and decoupling of shear strain are achieved; the dual sealing positions and high-temperature resistant material ensure long-term sealing reliability under strong radiation and high-temperature environments; the detection light source and spectral detection equipment are externally mounted to avoid damage to optical equipment from nuclear radiation and extend the device's service life.

[0020] In this application's technical solution, the fiber optic sensing unit is sealed and fixed to the fiber optic through-hole using high-temperature resistant adhesive and gold-tin eutectic brazing. This prevents micro-bending loss in the fiber. The sealing structure (especially the combination of metal-coated silica fiber and gold-tin brazing) provides physical shielding for the sensing part, delaying irradiation damage to the fiber core. When the bolt expands or contracts due to heat or is under pressure, the fiber optic cable may randomly bend or twist, resulting in severe "micro-bending loss" during transmission, preventing the spectral detection equipment from acquiring a valid signal. In reactor operation or vibration environments, gravity pendulums generate mechanical tensile or shear forces. A secure fixation prevents the fiber optic cable from shifting, breaking, or fatigue-damaging under long-term stress. Through sealing (e.g., using high-temperature resistant adhesive or gold-tin eutectic brazing), the fiber optic sensor is firmly bonded to the bolt body or the internal second strain beam. When the bolt undergoes slight deformation under stress, the deformation is transmitted to the fiber optic sensor 100% without loss, ensuring that the data acquired by the spectral detection equipment accurately reflects the bolt's strain level and guarantees the accuracy of strain transmission.

[0021] This invention significantly improves the detection accuracy of minute strains in nuclear reactor pressure vessel bolts by introducing a collaborative mechanism between fiber optic sensors and a gravity pendulum. Specifically, two second fiber optic sensors are embedded within the bolt body and connected to the gravity pendulum via a second strain beam, forming a highly sensitive detection system. When the bolt experiences minute strain, the second strain beam bends due to the change in force on the gravity pendulum, causing the pendulum to deviate from its initial position. This deviation causes a change in the reflected light signal from the fiber optic sensors, which is captured by a spectral detection device and transmitted to a strain calculation electronics device for analysis. Furthermore, this invention employs a differential strain detection principle, enabling precise capture of micron-level strains, further improving detection resolution and accuracy. Current verification experimental results show that this technology can effectively detect strains smaller than 10 micrometers in practical applications, demonstrating significant advantages over traditional methods.

[0022] This invention incorporates numerous optimizations in structural design and material selection to enhance the long-term stable operation of the device and reduce the impact of environmental factors on the detection results. First, the core component—the fiber optic sensor—utilizes a special radiation-resistant fiber optic material that is resistant to high temperatures and corrosion, ensuring stable performance even under the high-temperature, high-pressure, and strong radiation environment inside a nuclear reactor. Second, the sealed housing design effectively protects the fiber optic connectors and internal optical components from external contamination and mechanical damage. In particular, filling the sealed housing with an inert gas (such as helium or argon) not only reduces the risk of oxidation but also enhances the device's anti-interference capabilities, ensuring the accuracy and consistency of the detection results. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a nuclear reactor pressure vessel according to an embodiment of this application.

[0025] Figure 2 This is a schematic diagram of the structure of the nuclear reactor pressure vessel bolts according to an embodiment of this application.

[0026] Figure 3 This is a schematic diagram of the specific structure of the nuclear reactor pressure vessel bolt strain detection device and bolt connection provided in the embodiments of this application.

[0027] Figure 4 A schematic diagram of the specific structure of the strain detection device for the bolts of a nuclear reactor pressure vessel provided in this embodiment of the application.

[0028] Figure 5 for Figure 3 BB-direction cross-section view.

[0029] Figure 6 The diagram shows the state of the nuclear reactor pressure vessel bolt strain detection device before strain, as provided in the embodiments of this application.

[0030] Figure 7 A diagram showing the strain state of a nuclear reactor pressure vessel bolt strain detection device provided in an embodiment of this application.

[0031] Figure 8 The diagram shows the state of the nuclear reactor pressure vessel bolt strain detection device before torque stress, as provided in the embodiments of this application.

[0032] Figure 9 A state diagram of torque stress for a strain detection device for bolts of a nuclear reactor pressure vessel provided in an embodiment of this application.

[0033] Figure 10 for Figure 3 Enlarged view of point A.

[0034] Figure 11 This is a schematic diagram of the strain calculation electronic device for the strain detection device of the nuclear reactor pressure vessel bolts provided in the embodiments of this application. Detailed Implementation

[0035] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0036] like Figure 1 The diagram shows the structure of a nuclear reactor pressure vessel. Nuclear reactor pressure vessels are typically made of high-strength low-alloy steel, and their main body includes a cylindrical shell 1, a top cover 2, end caps 3, and nozzles for connecting various pipes and control devices. The design of the RPV must meet stringent nuclear safety standards to ensure effective prevention of radioactive material leakage under normal operation, abnormal conditions, and even accident scenarios. During long-term service, the main bolts 4 of the top cover may experience significant strain due to transient conditions such as temperature changes and pressure fluctuations, which can affect the sealing effect at the flange connection. Therefore, accurate strain detection of the main bolts 4 of the top cover is of significant engineering importance.

[0037] like Figure 2The diagram illustrates an application scenario of the nuclear reactor pressure vessel bolt strain detection device of this invention. During operation, the main bolts of a nuclear reactor pressure vessel face a complex mechanical environment, especially under transient conditions. The temperature hysteresis effect leads to a significant increase in the alternating stress amplitude of the main bolts, resulting in problems such as accumulated plastic deformation and changes in flange separation. These problems not only affect sealing performance but may also jeopardize the overall safety of the reactor. Currently, traditional physical measurement methods typically rely on external sensors or mechanical measuring tools, making real-time monitoring during bolt use difficult. Post-operation physical testing requires disassembling the bolts for offline analysis, failing to reflect the strain under operating conditions in a timely manner. Testing must be performed while the system is shut down, increasing maintenance costs and potentially causing production interruptions. This nuclear reactor pressure vessel bolt strain detection device for detecting torsional stress can be installed and fixed on the bolt nut and inside the bolt body of the main bolt 4 of the top cover, enabling real-time detection of shear strain inside the bolt body and torsional strain of the bolt nut.

[0038] like Figure 3 The diagram shows a schematic of a strain detection device for bolts in a nuclear reactor pressure vessel. The device includes: a detection light source 51 configured to provide incident light; a first strain beam 61, fixedly mounted on the outside of the bolt / nut, with one end limited by the nuclear reactor pressure vessel; a first fiber optic sensor 6, disposed inside the first strain beam 61, with its fiber optic lines at least partially parallel to the outer contour of the bolt / nut; both ends of the sensing portion of the fiber optic line of the first fiber optic sensor 6 are sealed and fixed to the first strain beam using high-temperature resistant material; the first fiber optic sensor 6 is configured to receive incident light and transmit reflected light to the spectral detection device; a spectral detection device 52 configured to receive the optical signal; and a strain calculation electronic device 57 configured to determine the degree of torsional strain of the bolt based on the difference in reflected light from the fiber optic sensor obtained by the spectral detection device before and after the bolt / nut's torsional strain. When the bolt / nut is subjected to a torsional moment, its outer contour surface will generate tangential shear strain. The first strain beam 61 is fixedly sleeved on the outside of the nut, with one end limited by a pressure vessel. When the nut twists, a relative displacement or shear deformation occurs between the strain beam 61 and the nut. This mechanical structure design cleverly transforms the torsional shear strain, which is difficult to measure directly, into the axial normal strain, which is most sensitive to and easily demodulated by fiber optic sensors. This enables real-time and accurate monitoring of bolt strain under complex working conditions. The device of this invention, by introducing a highly sensitive fiber optic sensor and an intelligent data processing module, effectively overcomes the shortcomings of traditional detection methods.

[0039] More specifically, such as Figures 4-10The diagram shows a structural schematic of a strain detection device for nuclear reactor pressure vessel bolts capable of simultaneously detecting torsional stress and shear strain. In addition to the aforementioned structure, the device includes two second fiber optic sensors 5 embedded within the bolt body. These sensors pass through a second strain beam 55 fixedly mounted within the bolt body. A deflectable gravity pendulum 56 is suspended from the lower end of the second strain beam 55. The fiber optic lines of the two second fiber optic sensors 5 passing through the second strain beam 55 are sealed with a high-temperature resistant material. The strain calculation electronics 57 is further configured to determine the strain level of the bolt body based on the deviation of the gravity pendulum 56 from the bolt body's axis, combined with the difference in reflected light from the second fiber optic sensors obtained by the spectral detection device. The embedded design of the second fiber optic sensors 5 effectively ensures the strain transfer efficiency between the second fiber optic sensors 5 and the bolt body, while minimizing the impact on the bolt's structural integrity, thereby meeting the safe operation requirements of nuclear reactor pressure vessel bolts under high stress conditions. In this device, the second fiber optic sensors are embedded at the central axis of the bolt body, penetrating the entire length of the bolt to ensure comprehensive sensing of strain changes generated during transverse shear stress.

[0040] Because the sensing ends of the first fiber optic sensor 6 are sealed and fixed to the first strain beam 61 with high-temperature resistant material, and the fiber optic cable is at least partially parallel to the outer contour of the nut, the torsional shear strain of the nut is forcibly transmitted to the first strain beam 61 and further converted into axial tensile or compressive strain of the first fiber optic sensor 6. This device, by embedding two second fiber optic sensors 5 within the bolt body and setting up a structure of a second strain beam 55 and a gravity pendulum 56, combined with a detection light source, spectral detection equipment, and strain calculation electronics, achieves high-precision detection of the transverse shear strain of the bolt under test. Specifically, when the bolt experiences strain, the gravity pendulum 56 on the second strain beam 55 deviates from the bolt axis, causing a difference in the reflected light signals from the two second fiber optic sensors 5. The strain calculation electronics determine the degree of strain based on this difference. By using the common-mode temperature signal from the dual sensors to eliminate the influence of ambient temperature fluctuations on the measurement results, the device ensures the measurement accuracy and reliability under nuclear reactor operating conditions, providing an important guarantee for the safe operation of the nuclear reactor.

[0041] like Figures 5-10As shown, the fiber optic sensor used in this invention employs radiation-resistant quartz fiber optic cable; preferably, the fiber optic cable is a metal-coated quartz fiber optic cable; preferably, the metal coating of the fiber optic cable is either a nickel coating or a gold coating. The fiber optic sensor uses radiation-resistant quartz fiber optic cable or metal-coated quartz fiber optic cable to enhance its stability and durability under nuclear radiation conditions. Since the operating environment of a nuclear reactor is typically accompanied by high temperatures, the selection of sealing materials must focus on their high-temperature resistance, sealing effect, and impact on signal transmission. Encapsulating the sensing part of the fiber optic sensor within the cable prevents other substances from affecting it during strain detection, thus ensuring detection accuracy. Radiation-resistant quartz fiber optic cable, due to its high purity and uniform refractive index distribution, can maintain stable optical performance under extreme conditions; while metal-coated quartz fiber optic cable further improves the reliability of the sensor by enhancing surface hardness and bending resistance. Experimental results show that the sensor using metal-coated quartz fiber optic cable exhibits lower signal drift and higher durability under high temperature and high pressure conditions.

[0042] In a preferred embodiment of the present invention, a first optical fiber through-hole is formed on the first strain beam 61, the optical fiber of the first optical fiber sensor 6 passes through the first optical fiber through-hole, the optical fiber sensing part of the sensor is disposed in the first optical fiber through-hole, and both ends are sealed and fixed to the optical fiber through-hole; the first strain beam 61 includes a strain part that is fixedly engaged with the bolt and nut and a mounting part integrally formed with the strain part, one end of the mounting part is limited by the nuclear reactor pressure vessel and is provided with the first optical fiber through-hole; the first optical fiber through-hole is partially parallel to the outer contour of the bolt and nut; preferably, when the bolt is a hexagonal bolt, the first optical fiber through-hole is parallel to at least one side of the outer contour of the hexagonal bolt and nut.

[0043] The second strain beam 55 is disposed within a sealed housing 531, which is fixedly sealed to an optical fiber connector 532 partially embedded in the bolt body. The optical fiber of the second optical fiber sensor 5 enters the sealed housing 531 through the optical fiber connector 532, and its sensing part is located within the second optical fiber through-hole opened in the second strain beam 55, with both ends sealed and fixed to the second optical fiber through-hole. The second optical fiber sensor 5 is configured to receive incident light and transmit reflected light to the spectral detection device. Preferably, a first sealing position 541 at the entrance and a second sealing position 542 at the exit are provided on both the second optical fiber through-hole and the first optical fiber through-hole. Through the sealing structure (especially the combination of metal-coated quartz optical fiber and gold-tin brazing), physical shielding can be provided for the sensing part, delaying the damage of irradiation to the fiber core.

[0044] In a preferred embodiment, the fiber optic extension direction of the second fiber optic sensor 5 is perpendicular to the fiber optic extension direction of the first fiber optic sensor 6; both ends of the first fiber optic sensor 6 and the second fiber optic sensor 5 are sealed and fixed with high-temperature resistant materials, which not only ensures the stability of mechanical strain transmission under high temperature and high pressure conditions, but also avoids damage to the optical fiber caused by coolant erosion. The all-fiber passive sensing mechanism naturally possesses anti-electromagnetic interference and explosion-proof characteristics, perfectly meeting the intrinsic safety requirements of nuclear facilities.

[0045] When the optical fiber of the fiber optic sensor is located at the first sealing position 541, it is sealed by gold-tin eutectic brazing and then a secondary seal is applied using high-temperature resistant adhesive; when the optical fiber of the fiber optic sensor is located at the second sealing position 542, it is sealed by gold-tin eutectic brazing and then a secondary seal is applied using high-temperature resistant adhesive; preferably, the solder used for the gold-tin eutectic brazing is Au80Sn20 gold-tin eutectic solder; preferably, the high-temperature resistant adhesive is silicone adhesive, polyimide adhesive, or epoxy adhesive. Gold-tin eutectic brazing, as a highly efficient sealing technology, plays an important role in the sealing of optical fibers. This process utilizes the eutectic structure formed by Au80Sn20 gold-tin eutectic solder at a specific temperature to achieve a reliable connection between the optical fiber and the sealing structure. Au80Sn20 solder, due to its low melting point (approximately 280°C), good wettability, and excellent mechanical properties, is an ideal choice for sealing optical fibers in high-temperature environments. In practical applications, the gold-tin eutectic brazing process, by precisely controlling parameters such as heating temperature, holding time, and cooling rate, can effectively avoid fiber damage caused by thermal stress, while ensuring the long-term stability of the sealed joint. The advantages of the gold-tin eutectic brazing process are not only reflected in its superior sealing effect but also in its adaptability to complex structures. During the fiber optic cable's passage through the strain gauge beam, traditional sealing methods often struggle to achieve a complete seal due to the presence of fiber optic vias. The gold-tin eutectic brazing process, with its excellent flowability and filling capacity, effectively solves this problem, ensuring that the sealing quality of the fiber optic cable at the strain gauge beam meets design requirements. Furthermore, this process exhibits high repeatability and reliability, making it suitable for large-scale production applications.

[0046] This invention relates to a strain detection device for bolts in nuclear reactor pressure vessels, designed for detecting torsional stress. The device achieves high-precision real-time monitoring of bolt strain through the coordinated operation of a detection light source, a spectral detection device, a fiber optic sensor, a second strain beam 55, and a gravity pendulum 56. Its design fully considers the extreme environments of nuclear reactors, such as high temperature, high pressure, and strong neutron radiation, and possesses characteristics such as high strength, high toughness, resistance to radiation embrittlement, and resistance to stress corrosion. Experimental results show that this detection device effectively solves the problems in existing technologies, providing important assurance for the safe operation of nuclear power plants. Furthermore, its technical principles can be extended to the monitoring of equipment in other similar complex environments.

[0047] In a specific embodiment of the present invention, the device embeds an optical fiber connector within the bolt body and connects it to a sealed housing via a fixed sealing structure. Specifically, the sealed housing is filled with an inert gas; the design of the sealed housing not only effectively protects the internal optical fiber sensor and other critical components but also further enhances the stability and reliability of the device by filling it with an inert gas. Specifically, the inert gas filling the sealed housing can be one or more mixed gases selected from helium, argon, nitrogen, neon, or krypton. Filling the sealed housing with an inert gas, such as helium or argon, provides good environmental isolation and heat dissipation performance. The filling pressure of the inert gas is controlled between 0.2 MPa and 0.5 MPa to prevent the infiltration of external media and improve the radiation resistance of the housing. These inert gases have good chemical and thermal stability, maintaining their performance under harsh environments such as high temperature and high pressure, thereby reducing the impact of environmental factors on the detection results. Furthermore, the fixed sealing structure between the optical fiber connector 532 and the sealed housing 531 effectively prevents the entry of external impurities, avoiding signal attenuation or measurement errors caused by contamination. Experimental results show that the detection accuracy and long-term stability of the device are significantly improved after adopting this preferred implementation method.

[0048] In a specific embodiment of the present invention, the second strain beam 55 is fixedly installed inside the sealed housing 531. At least two second optical fiber through-holes 533 are formed on the second strain beam 55. The optical fibers of the two second optical fiber sensors 5 are symmetrically arranged on both sides of the second strain beam 55. After passing through optical fiber connectors 532, the optical fibers of the two second optical fiber sensors 5 enter the second optical fiber through-holes 533 within the sealed housing and are sealed and fixed to the through-holes. Specifically, the second strain beam 55 is installed inside the sealed housing 531 by fasteners to ensure that it will not loosen or shift during long-term use. Furthermore, at least two second optical fiber through-holes are formed on the second strain beam 55 for fixing the optical fibers of the two second optical fiber sensors 5. After entering the second optical fiber through-holes, the optical fibers are sealed and fixed to the through-holes with high-temperature resistant adhesive, thereby further enhancing the stability of the device. The present invention recommends using adhesives with a temperature resistance range of over 400°C to meet the operational requirements of nuclear reactor pressure vessels in high-temperature environments and to maintain long-term stability in the high-temperature environment of nuclear reactors. Experiments show that fixing the optical fiber with high-temperature resistant adhesive results in superior performance under extreme temperature conditions, and significantly improves the signal transmission stability of the optical fiber sensor. This fixing method not only enhances the mechanical strength of the device but also reduces signal interference caused by vibration or temperature changes, thus providing strong support for high-precision detection.

[0049] Two second fiber optic sensors are symmetrically embedded on the central axis of the bolt body, with their sensing parts located within the effective tensile region of the bolt to directly sense strain changes during stress. The embedding depth of the second fiber optic sensors is designed based on the specific dimensions and stress characteristics of the bolt, typically ranging from 2 / 3 to 4 / 5 of its total length, to ensure that the sensors fully cover the high-stress areas of the bolt. During embedding, the fiber optic sensors are fixed by infusing with high-temperature resistant epoxy resin to prevent displacement or loosening during use. Since nuclear reactor operation typically involves high-temperature conditions, the selection of sealing materials must prioritize their high-temperature resistance, sealing effect, and impact on signal transmission. Silicone sealant, polyimide sealant, and epoxy sealant are preferred high-temperature resistant sealing materials, which can reduce stress concentration caused by thermal expansion and protect the fiber optic cables from mechanical damage.

[0050] In a specific embodiment of the present invention, the sensing portions 540 of the two second fiber optic sensors 5 are located at the portion where the fiber optic lines of the second fiber optic sensors 5 enter the second strain beam 55; more preferably, the fiber optic lines of the two second fiber optic sensors 5 terminate at the lower end face of the second strain beam 55 after entering the second strain beam 55; specifically preferably, the sensing portions 540 of the two second fiber optic sensors 5 are at the same height level. The sensing portions 540 of the two second fiber optic sensors 5 are located at the portion where their fiber optic lines enter the second strain beam 55, and the fiber optic lines terminate at the lower end face of the second strain beam 55 after entering the second strain beam 55. To ensure that the sensing portions 540 are at the same level, this application employs precision machining and calibration processes, strictly controlling the length and position of the fiber optic lines to ensure the consistency of the sensing portions 540 of the two second fiber optic sensors 5 in the height direction. The importance of this design lies in the fact that when the bolt experiences transverse shear strain, the second strain beam 55 will uniformly transmit the stress to the two second fiber optic sensors 5, and the fact that the sensing portions 540 are at the same height level can effectively avoid measurement errors caused by height differences. Experimental results show that the detection accuracy of the device is significantly improved after adopting this preferred embodiment, especially in the detection of minute strains. The two second fiber optic sensors 5 are two radiation-resistant fiber optic sensors of the same specification, preferably radiation-resistant quartz fiber optic sensors. This also avoids the influence of temperature fluctuations on the measurement results, as the temperature of the other second fiber optic sensor 5 can be calibrated by one of the two second fiber optic sensors 5.

[0051] In a specific embodiment of the present invention, a first gap D1 is provided between the lower end face of the second strain beam 55 and the upper end face of the gravity pendulum 56, and the distance between the optical fibers of the two second optical fiber sensors 5 and the lower end face of the second strain beam 55 after entering the second strain beam 55 is greater than or equal to the first gap D1. Preferably, the suspension connection 534 between the gravity pendulum 56 and the second strain beam 55 is located at the center of the lower end face of the second strain beam 55. The present invention provides a detailed design for the gap between the lower end face of the second strain beam 55 and the upper end face of the gravity pendulum 56. Specifically, a first gap is provided between the lower end face of the second strain beam 55 and the upper end face of the gravity pendulum 56, and the distance between the optical fibers of the two second optical fiber sensors 5 and the lower end face of the second strain beam 55 after entering the second strain beam 55 is greater than or equal to the first gap. This design effectively prevents the optical fibers from being squeezed or stretched during the deflection of the gravity pendulum 56, thereby avoiding signal distortion caused by mechanical stress. Furthermore, the suspension connection between the gravity pendulum 56 and the second strain beam 55 is located at the center of the lower end face of the second strain beam 55. This symmetrical design ensures that the gravity pendulum 56 remains balanced during deflection, thus providing a more accurate reference for strain detection. Experimental results show that the strain detection accuracy of the device is significantly improved after adopting this preferred embodiment, especially its detection performance under complex working conditions is even better.

[0052] In a specific embodiment of the present invention, the sealed housing 531 is a blind end at the lower end of the gravity pendulum 56, and the cavity of the blind end is filled with inert gas. In a specific embodiment, a sealing cover is provided at the lower end of the sealed housing of the gravity pendulum 56, the sealing cover is filled with inert gas, and the lower end of the gravity pendulum 56 is free. Regarding the setting of the blind end or sealing cover at the lower end of the gravity pendulum 56, the present invention provides two optional solutions: one is to adopt a blind end structure and fill the cavity of the blind end with inert gas to enhance the sealing and stability of the device; the other is to adopt a sealing cover structure, the sealing cover is filled with inert gas, and the lower end of the gravity pendulum 56 remains free, so that the gravity pendulum 56 can flexibly deflect under external forces. Furthermore, the connection and fit between the second strain beam 55 and the fiber optic connector and the sealed housing are also carefully designed, and the influence of mechanical stress on the fiber optic sensor is reduced by optimizing the connection structure. Regarding the positional relationship between the gravity pendulum 56 and the second strain beam 55, the present invention ensures that the center of the upper end face of the gravity pendulum 56 and the center of the lower end face of the second strain beam 55 are located on the axis of the sealed shell, and the area of ​​the upper end face of the gravity pendulum 56 is less than or equal to the area of ​​the lower end face of the second strain beam 55, thereby avoiding measurement errors caused by excessive deflection range of the gravity pendulum 56.

[0053] To prevent mechanical damage to the fiber optic sensor during embedding, a flexible metal sheath is wrapped around the fiber optic cable. This sheath not only provides additional mechanical protection but also enhances the sensor's radiation resistance. Furthermore, after entering the bolt body, the fiber optic cable gradually transitions to a straight state through a transition region to reduce bending loss during optical signal transmission. To ensure good adhesion between the fiber optic sensor and the bolt body, the inner surface of the bolt is sandblasted before embedding to improve surface roughness and enhance bond strength. Experimental results show that the fiber optic sensor fixed using the above embedding method exhibits excellent stability and sensitivity during long-term operation, meeting the high requirements for strain detection of bolts in nuclear reactor pressure vessels.

[0054] In a specific embodiment of the present invention, the device further includes a third optical fiber sensor. The optical fibers of the two second optical fiber sensors 5 and the third optical fiber sensor extend along the axis of the sealed housing and are evenly distributed circumferentially along the axis of the sealed housing. The present invention also proposes an additional third optical fiber sensor, where the optical fibers of the two second optical fiber sensors 5 and the third optical fiber sensor extend along the axis of the sealed housing and are evenly distributed circumferentially along the axis of the sealed housing, to further improve detection accuracy.

[0055] In a specific embodiment of the present invention, the upper end of the second strain beam 55 is fixed to the optical fiber connector 532; preferably, the side of the second strain beam 55 is clearance-fitted with the sealed housing. The second strain beam 55 adopts a cantilever beam structure, and its length, width, and thickness are designed according to the specific bolts. This second strain beam 55 can bend and deform when the bolts experience small strain, thereby amplifying the strain signal and transmitting it to the second optical fiber sensor 5. The material of the second strain beam 55 is high-strength low-alloy steel, which has excellent resistance to radiation embrittlement and stress corrosion, and can maintain long-term stability in the complex environment of a nuclear reactor. In addition, the surface of the second strain beam 55 is precision polished to reduce the impact of surface roughness on optical signal transmission.

[0056] like Figure 10As shown, the center of the upper end face of the gravity pendulum 56 and the center of the lower end face of the second strain beam 55 are located on the axis of the sealed shell, and the area of ​​the upper end face of the gravity pendulum 56 is less than or equal to the area of ​​the lower end face of the second strain beam 55; preferably, the orthographic projections of the upper end face of the gravity pendulum 56 and the lower end face of the second strain beam 55 onto the lower end face of the second strain beam 55 are concentric circles, and the area of ​​the upper end face of the gravity pendulum 56 is less than the area of ​​the lower end face of the second strain beam 55. The sensing parts of the two second fiber optic sensors 5 are located in the middle or lower region of the second strain beam 55 to maximize the sensing of strain changes. The two second fiber optic sensors are bonded and fixed to the second strain beam 55 with high-temperature resistant adhesive, and the thickness of the adhesive layer is controlled within 0.1 mm to reduce the influence of the adhesive layer on strain transmission. The gravity pendulum 56 is suspended from the center of the lower end face of the second strain beam 55 by a flexible metal strip. The suspension point is designed to consider the balance and sensitivity of the gravity pendulum 56, ensuring a rapid response when the second strain beam 55 undergoes minor deformation. Experimental results show that the second strain beam 55 with the above design exhibits good linear response characteristics and high sensitivity under simulated operating conditions, meeting the requirements for strain detection of bolts in nuclear reactor pressure vessels.

[0057] The sensitivity principle of the gravity pendulum 56 is based on the high sensitivity of its center of mass position change to the bending deformation of the second strain beam 55. When the bolt experiences axial tensile or compressive strain, the suspension point of the gravity pendulum 56 shifts, causing a corresponding bending deformation in the second strain beam 55. Since the center of mass position of the gravity pendulum 56 is fixed, there is a clear mathematical relationship between its swing angle and the bending deformation of the second strain beam 55. The swing angle of the gravity pendulum 56 can be measured by the changes in two second fiber optic sensors, allowing for the indirect calculation of the bending deformation of the second strain beam 55, and thus the derivation of the bolt's strain level. Experimental results show that the gravity pendulum 56 design can achieve high-precision detection within a micro-strain range, with a sensitivity of up to 0.01 mm / m, meeting the high requirements for strain detection of bolts in nuclear reactor pressure vessels.

[0058] In a preferred embodiment of the present invention, the device further includes an optical fiber coupler 58, which is configured to transmit the probe light emitted by the probe light source 51 to the optical fiber lines of the two optical fiber sensors, and to transmit the reflected light from the optical fiber lines to the spectral detection device 52. The strain calculation electronics is an electronic device equipped with a strain calculation module; specifically, preferably, the optical fiber coupler 58 is an optical circulator. The present invention also introduces an optical fiber coupler for transmitting the probe light emitted by the probe light source to the optical fiber lines of the optical fiber sensors, and transmitting the reflected output light from the optical fiber lines to the spectral detection device. The application of the optical fiber coupler not only simplifies the optical path design but also improves the signal transmission efficiency, thus providing strong support for the overall performance optimization of the device. The probe light source uses a narrow-linewidth laser as the light source, and the emitted probe light has high monochromaticity and coherence, which can significantly improve the detection accuracy. The spectral detection device has a built-in high-sensitivity photodetector and a signal processing module, which can convert the received optical signal into an electrical signal and perform preliminary processing, providing a reliable data foundation for subsequent strain calculations.

[0059] During operation, the detection light emitted by the detection source is first transmitted to the incident end of the fiber optic sensor through an optical fiber coupler, and then coupled into the fiber and propagates along the fiber. On one hand, because the second fiber optic sensor is embedded in the bolt body, when the bolt experiences strain, the optical signal in the fiber changes in wavelength or intensity due to the strain effect. These changing optical signals are ultimately transmitted to a spectral detection device, which demodulates and analyzes the signal. By comparing the difference between the input and output light, the shear strain information of the bolt can be accurately obtained. On the other hand, when the bolt experiences torsional strain, the process of the strain being transmitted to the fiber optic sensor through the first strain beam involves a complex mechanical and optical coupling mechanism. Specifically, the bolt generates shear strain during torsion, which is converted into axial strain of the first strain beam and further acts on the optical fiber in the fiber optic sensor, causing a change in stress distribution inside the fiber, which in turn causes a shift in the wavelength or intensity of the optical signal. Because the fiber optic sensor's fiber lines are partially parallel to the outer contour of the bolt / nut, this layout further enhances the sensitivity to strain, thereby improving detection accuracy.

[0060] For fiber Bragg grating (FBG) sensors, the core working principle is to sense external strain by utilizing the periodic refractive index change in the fiber. When strain is transmitted to the fiber sensor, the fiber's geometry and internal stress distribution change, causing modulation of the phase and wavelength of the light propagating in the fiber. According to coupled-mode theory, the reflected wavelength of the fiber Bragg grating changes linearly with external strain, and this relationship can be expressed as Δλ / λ=κε, where Δλ is the wavelength shift, λ is the initial wavelength, κ is the strain sensitivity coefficient, and ε is the applied strain. Spectroscopic detection equipment typically employs demodulation techniques based on interferometers or diffraction gratings to convert the wavelength change of the optical signal into an electrical signal output. For example, a high-resolution measurement of the reflected wavelength of a fiber Bragg grating can be achieved using an unbalanced Mach-Zehnder interferometer (MZI), which works by inverting the wavelength shift through the movement of interference fringes. In the signal processing stage, the spectroscopic detection equipment filters, amplifies, and digitizes the acquired electrical signal to remove noise interference and improve the signal-to-noise ratio. Subsequently, the strain calculation electronic device calculates the processed optical signal data based on the pre-calibrated strain-wavelength relationship model, and finally obtains the torsional strain and shear strain of the bolt.

[0061] More preferably, such as Figure 8 and Figure 9 As shown, there are multiple first fiber optic sensors, evenly distributed inside the first strain beam 61. Their fiber optic lines are at least partially parallel to the outer contour of the bolts and nuts. The two ends of the sensing portion of the first fiber optic sensor 6 are sealed and fixed to the first strain beam 61 using a high-temperature resistant material. This distributed design of the first fiber optic sensors eliminates errors caused by temperature cross-sensitivity and avoids the influence of temperature effects on the optical signal changes within the fiber optic sensors.

[0062] On the other hand, the sensing element in the second fiber optic sensor is located near the second strain beam 55. When the probe light passes through this region, due to the presence of the second strain beam 55 and its possible minute strain, the light signal will undergo phenomena such as scattering, refraction, or absorption, resulting in a significant difference between the output light and the input light. Furthermore, the spectral detection equipment, through high-precision spectral analysis technology, can accurately measure the changes in the spectral characteristics of the output light, providing reliable data support for subsequent strain calculations.

[0063] When the bolt experiences strain, the second strain beam 55, as a key component, drives the movement of the fiber optic sensors and the gravity pendulum 56, resulting in changes in the optical signal. The specific mechanism of this change can be explained through dynamic analysis of the second strain beam 55 and the gravity pendulum 56. First, the design of the second strain beam 55 allows it to generate elastic strain when subjected to external stress. This strain is directly transmitted to the two second fiber optic sensors 5 fixed to the surface of the second strain beam 55. Due to the extremely high sensitivity of fiber optic sensors to mechanical strain, the refractive index distribution between the fiber core and cladding changes with strain, thereby causing changes in the phase, intensity, or polarization state of the optical signal. Simultaneously, the presence of the gravity pendulum 56 further enhances the system's ability to sense strain. When the bolt experiences axial or radial strain, the lower end of the second strain beam 55 deflects, causing the gravity pendulum 56 to deviate from its initial equilibrium position. This deviation leads to a change in the relative positions between the fiber optic sensors, thus amplifying the differences in the optical signal.

[0064] The strain calculation electronic device accurately calculates the strain of the bolt by analyzing the differences in the optical signals acquired by the spectral detection device and considering the specific circumstances of the gravity pendulum 56's deviation from the bolt axis. Its core algorithm is based on the relationship between the phase difference of the optical signals and the deflection angle of the gravity pendulum 56. First, the spectral detection device measures and records the output optical signals of the two second fiber optic sensors 5, including their wavelength, intensity, and phase information. Since the two fiber optic sensors are relatively fixed and close together, the difference in their output optical signals mainly originates from the motion of the second strain beam 55 and the gravity pendulum 56. Second, the strain calculation electronic device uses the principle of interferometry to determine the strain of the second strain beam 55 by analyzing the phase difference of the output optical signals. Specifically, the phase difference of the optical signals is proportional to the strain of the second strain beam 55, and its proportionality coefficient can be obtained through experimental calibration. Furthermore, the deflection angle of the gravity pendulum 56 is geometrically related to the strain of the second strain beam 55. For example, when the gravity pendulum 56 deviates from the bolt axis by a certain angle, the strain of the second strain beam 55 can be calculated using trigonometric functions. Finally, the strain calculation electronic device, combining the data from the optical signal phase difference and the deflection angle of the gravity pendulum 56, calculates the strain degree of the bolt using the following formula: ε = KΔφ / L, where ε represents the strain, K is the proportionality coefficient, Δφ is the optical signal phase difference, and L is the effective length of the second strain beam 55. Through this method, the detection device can achieve high-precision measurement of bolt shear strain, providing crucial assurance for the safe operation of nuclear reactors.

[0065] Furthermore, to further improve the system's anti-interference capability, a shielded cable is used to connect the detection light source and the spectral detection equipment, and an electromagnetic shielding layer is installed on the equipment casing to reduce the impact of electromagnetic radiation on signal transmission. For example... Figure 11As shown, the strain calculation electronic device of the present invention includes: a memory 220 for storing instructions; and a processor 210 for executing the instructions to enable the device to implement the strain calculation method described above. More specifically, the electronic device also includes a communication module. In this solution, the processor may include one or more processing units. For example, the processor may include one or more of the following: application processor (AP), modem, graphics processing unit (GPU), image signal processor (ISP), controller, video codec, digital signal processor (DSP), baseband processor, and / or neural-network processing unit (NPU). Different processing units may be independent devices or integrated into one or more processors.

[0066] The memory 220 may store a program, which can be executed by the processor 210, causing the processor 210 to perform the methods provided in this application. The memory 220 may also store data. The processor 210 may read the data stored in the memory 220. The memory 220 and the processor 210 may be configured separately. Optionally, the memory 220 may also be integrated into the processor 210.

[0067] The communication module 230 may include at least one of a mobile communication module and a wireless communication module. When the communication module 230 includes a mobile communication module, it can provide wireless communication solutions, including 2G / 3G / 4G / 5G, applied to the electronic device 200. In the above embodiments, it can be implemented entirely or partially through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented entirely or partially in the form of a computer program product.

[0068] This detection device significantly enhances its environmental adaptability by employing high-strength materials in the manufacture of key components and incorporating inert gas protection technology. For example, the design of the second strain beam 55 and the fiber optic sensor fully considers the radiation resistance of the materials, avoiding material embrittlement caused by long-term neutron radiation. Furthermore, the inert gas (such as helium or argon) filling the sealed casing effectively isolates the second strain beam 55 and the fiber optic sensor from the external environment, further enhancing the device's resistance to stress corrosion. These designs enable the detection device to maintain high accuracy and reliability in the complex operating environment of a nuclear reactor, thus meeting practical application requirements. Due to the high sensitivity and electromagnetic interference resistance of the fiber optic sensor, it can accurately capture changes in optical signals caused by bolt strain, providing reliable data support for subsequent calculations. This detection device has the function of real-time monitoring of bolt strain, which is of great significance for ensuring the safe operation of a nuclear reactor. During the operation of a nuclear power plant, bolt strain may gradually accumulate due to factors such as temperature fluctuations, pressure changes, or material aging. If not detected and addressed in time, it may lead to sealing failure or even structural damage. By introducing real-time monitoring capabilities, this detection device can immediately issue an alarm when bolt strain exceeds a safety threshold, thereby providing timely decision support for maintenance personnel.

[0069] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A strain testing device for bolts of a nuclear reactor pressure vessel used to detect torsional stress, characterized in that, include: The detection light source is configured to provide incident light; The first strain beam is fixedly sleeved on the outside of the bolt and nut, and one end of it is limited by the nuclear reactor pressure vessel; A first fiber optic sensor is disposed inside the first strain beam. Its fiber optic line is at least partially parallel to the outer contour of the bolt and nut. Both ends of the sensing part of the first fiber optic line are sealed and fixed to the first strain beam by a high-temperature resistant material. The first fiber optic sensor is configured to receive incident light and transmit reflected light to the spectral detection device. The spectral detection equipment is configured to receive optical signals; The strain calculation electronic device is configured to determine the degree of torsional strain of the bolt based on the difference in reflected light from the first fiber optic sensor obtained by the spectral detection device before and after the bolt and nut torsional strain.

2. The strain detection device for bolts of a nuclear reactor pressure vessel according to claim 1, characterized in that, A first optical fiber through hole is opened on the first strain beam, the optical fiber of the first optical fiber sensor passes through the first optical fiber through hole, the optical fiber sensing part is disposed in the first optical fiber through hole, and both ends are sealed and fixed to the first optical fiber through hole. Preferably, the first strain beam includes a strain portion that is fixedly engaged with the bolt and nut and an installation portion integrally formed with the strain portion. One end of the installation portion is limited by the nuclear reactor pressure vessel and is provided with the first optical fiber through hole. Preferably, the first optical fiber through-hole is partially parallel to the outer contour of the bolt and nut; preferably, when the bolt is a hexagonal bolt, the first optical fiber through-hole is parallel to at least one side of the outer contour of the hexagonal bolt and nut.

3. The strain detection device for nuclear reactor pressure vessel bolts according to claim 2, characterized in that, The device further includes a second optical fiber sensor, wherein the optical fiber extension direction of the second optical fiber sensor is perpendicular to the optical fiber extension direction of the first optical fiber sensor. Preferably, the device further includes an optical fiber connector, through which the optical fiber of the first optical fiber sensor enters the first optical fiber through-hole, and its sensing part is disposed in the first optical fiber through-hole. Preferably, the device further includes a second strain beam disposed within a sealed housing. The sealed housing is fixedly sealed to an optical fiber connector partially embedded in the bolt body. The optical fiber of the second optical fiber sensor enters the sealed housing through the optical fiber connector, and its sensing part is located within the second optical fiber through-hole opened in the second strain beam, with both ends sealed and fixed to the second optical fiber through-hole. The second optical fiber sensor is configured to receive incident light and transmit reflected light to the spectral detection device. Preferably, both the second optical fiber through-hole and the first optical fiber through-hole are provided with a first sealing position at the inlet and a second sealing position at the outlet; Preferably, the optical fiber lines of the first and second optical fiber sensors are radiation-resistant quartz optical fiber lines. Preferably, the optical fibers of the first and second optical fiber sensors are metal-coated quartz optical fibers. Preferably, the optical fiber metal coating of the first and second optical fiber sensors is either a nickel coating or a gold coating.

4. The strain detection device for bolts of a nuclear reactor pressure vessel according to claim 3, characterized in that, The fiber optic sensor's fiber optic cable is sealed by gold-tin eutectic brazing at the first sealing position and then sealed a second time with high-temperature resistant adhesive. Preferably, the optical fiber of the optical fiber sensor is sealed by gold-tin eutectic brazing at the second sealing position and then sealed a second time with high-temperature resistant adhesive. Preferably, the solder used for the gold-tin eutectic brazing seal is Au80Sn20 gold-tin eutectic solder; Preferably, the high-temperature resistant adhesive is one of silicone adhesive, polyimide adhesive, or epoxy adhesive; Preferably, the high-temperature resistant adhesive is selected from adhesives with a temperature resistance range of 400°C or higher.

5. The strain detection device for nuclear reactor pressure vessel bolts according to claim 3, characterized in that, The detection light source and the spectral detection device are disposed outside the bolt body; Preferably, the second strain beam is disposed between the two second fiber optic sensors, and the strain calculation electronic device determines the degree of shear strain of the bolt body based on the difference in reflected light between the two second fiber optic sensors obtained by the spectral detection device; Preferably, the device further includes an optical fiber connector partially embedded in the bolt body and a sealed housing that is fixedly sealed with the optical fiber connector, and the optical fiber lines of the two second optical fiber sensors enter the sealed housing through the optical fiber connector; Preferably, the sealed housing is filled with inert gas; Preferably, the inert gas is selected from one or more of helium, argon, nitrogen, neon, and krypton; Preferably, the fiber optic cables of the two second fiber optic sensors are symmetrically arranged on both sides of the second strain beam. After passing through the fiber optic connector, the fiber optic cables of the two second fiber optic sensors enter the second fiber optic through-holes in the sealed housing and are sealed and fixed with the second fiber optic through-holes.

6. The strain detection device for nuclear reactor pressure vessel bolts according to claim 5, characterized in that, The sensing part of the two second optical fiber sensors is located at the part where the optical fiber line enters the second optical fiber through hole; Preferably, the optical fibers of the two second optical fiber sensors terminate at the lower end face of the second strain beam after entering the second strain beam; Preferably, the sensing parts of the two second fiber optic sensors are at the same height level; A first gap is provided between the lower end face of the second strain beam and the upper end face of the gravity pendulum, and the distance between the optical fiber lines of the two second optical fiber sensors and the lower end face of the second strain beam after entering the second strain beam is greater than or equal to the first gap. Preferably, the suspension connection between the gravity pendulum and the second strain beam is located at the center of the lower end face of the second strain beam; The sealed shell is a blind end at the lower end of the gravity pendulum, and the cavity of the blind end is filled with inert gas. Preferably, the sealed housing is provided with a sealing cover at the lower end of the gravity pendulum, the cavity inside the sealing cover is filled with inert gas, and the lower end of the gravity pendulum is free.

7. The strain detection device for bolts of a nuclear reactor pressure vessel according to claim 5, characterized in that, The upper end of the second strain beam is fixed to the optical fiber connector; Preferably, the side of the second strain beam is in clearance fit with the sealed shell; Preferably, the center of the upper end face of the gravity pendulum and the center of the lower end face of the second strain beam are located on the axis of the sealed shell, and the area of ​​the upper end face of the gravity pendulum is less than or equal to the area of ​​the lower end face of the second strain beam. Preferably, the upper end face of the gravity pendulum and the lower end face of the second strain beam are concentric circles when projected onto the lower end face of the second strain beam, and the area of ​​the upper end face of the gravity pendulum is smaller than the area of ​​the lower end face of the second strain beam.

8. The strain detection device for nuclear reactor pressure vessel bolts according to claim 5, characterized in that, The device further includes a third fiber optic sensor, wherein the fiber optic lines of the second fiber optic sensor and the third fiber optic sensor extend along the axis of the sealed housing and are uniformly distributed circumferentially according to the axis of the sealed housing.

9. The strain detection device for bolts of a nuclear reactor pressure vessel according to claim 1, characterized in that, The device further includes an optical fiber coupler configured to transmit probe light emitted from the probe light source to the optical fiber line of the optical fiber sensor, and to transmit reflected light from the optical fiber line to the spectral detection device.

10. The strain detection device for bolts of a nuclear reactor pressure vessel according to claim 9, characterized in that, The strain calculation electronic device is an electronic device equipped with a strain calculation module; preferably, the fiber optic coupler is an optical circulator.

Images