Reactor rod position measuring system

Abstract

The invention relates to a reactor rod position measuring system which comprises a front-end laser collimation unit, a rear-end laser transceiving unit and a transmission medium, the front-end laser collimation unit is mounted below a control rod reduction gearbox in a reactor safety container, is arranged opposite to a control rod and is of a pure optical structure without an electronic element; the rear-end laser transceiving unit is deployed outside the safety container and is physically isolated from the front-end laser collimation unit through an electrical penetration piece; the transmission medium connects the two and is used for transmitting a laser signal and receiving an echo signal; the range finder of the rear-end unit adopts a phase method, the front-end unit enables laser to irradiate the surface of the control rod, echo signals are obtained through natural diffuse reflection of the laser, and a reflector does not need to be installed. Through a front and rear end separation structure, damage of high temperature and irradiation to an electronic device is avoided, and in-pile complex working conditions are adapted; by combining a phase method and diffuse reflection design, the failure risk of the reflector is avoided, and the full-stroke high-precision absolute measurement of the control rod is realized.

Description

Technical Field

[0001] This invention relates to data measurement, and more specifically to a reactor rod position measurement system. Background Technology

[0002] The reactor control rod position measurement subsystem is a core component of the reactor rod control position system. Its core function is to monitor the real-time position information of the control rods in the reactor core during reactor startup, power regulation, shutdown, and emergency shutdown, which is directly related to the safety and reliability of reactor operation.

[0003] In various reactors, including Generation III, Generation III+ pressurized water reactors, Generation IV high-temperature gas-cooled reactors, and thorium-based molten salt reactors, control rod drive mechanisms mostly employ chain-type or wire rope hub-type transmission systems. The corresponding rod position measurement schemes are primarily based on indirect measurement principles, using relative position measuring devices such as synchros, encoders, and rotary transformers. These devices are installed in direct mechanical contact with the drive mechanism to convert the linear displacement of the control rods into angular signals for measurement. However, after a period of operation, if the accumulated measurement error of the position measuring equipment exceeds the limit, or if the rod position measurement PLC unexpectedly loses power, or if the rod position measurement system is re-energized after a major overhaul of the control rod drive mechanism, a "zero-finding" operation must be performed again, which is inconvenient. Indirect measurement cannot directly reflect the actual operating condition of the control rod drive mechanism. When faults such as idling, chain skipping, chain slippage, rod jamming, or chain jamming occur, the real-time position information of the control rods cannot be obtained, easily leading to safety hazards.

[0004] For advanced reactors such as thorium-based molten salt reactors, their special operating conditions place higher demands on the rod position measurement system. On the one hand, the measurement needs to be carried out in a confined space below the control rod deceleration box within the safety container, facing extreme environments such as high temperature, high radiation, and strong vibration. When traditional integrated laser rangefinders are built-in, their optical components and electronic devices are prone to performance degradation or even functional failure due to high-temperature thermal aging and radiation ionization effects. On the other hand, thorium-based molten salt reactors require continuous, accurate, and direct rod position measurement, requiring a measurement stroke covering 0~4m, an accuracy of ±3mm, and compatibility with the control rod movement speed of 5~15mm / s. Existing indirect measurement schemes are difficult to meet the absolute measurement requirements of high precision and long stroke.

[0005] To address the shortcomings of indirect contact measurements, the industry has experimented with various non-contact measurement technologies, but all have significant limitations: laser triangulation, while highly accurate, has a range of approximately 1000mm, which cannot cover the 0-4m working stroke of the control rod; laser interferometry, while achieving submicron accuracy, is sensitive to environmental vibrations and temperature fluctuations, and its optical path calibration is complex and costly, making it unsuitable for the harsh conditions of reactors; pulsed laser ranging, while simple in structure and capable of long-distance measurement, only achieves centimeter-level accuracy, failing to meet the high precision requirement of ±3mm.

[0006] Furthermore, traditional laser ranging solutions rely on the principle of mirror reflection to achieve signal feedback. However, in a thorium-based molten salt reactor environment, mirrors cannot be installed on the control rod end face: high-temperature irradiation will cause the mirror adhesive to fail and the mechanical structure to be damaged. Molten salt vapor in the reactor will adhere to the mirror surface and destroy the mirror reflection light path. Moreover, mirror reflection has extremely high requirements for optical parameters such as optical path collimation, which further limits the application of this type of solution.

[0007] In summary, existing reactor control rod position measurement technologies generally suffer from problems such as poor adaptability to non-contact measurement, difficulty in balancing high precision with adaptability to harsh environments, lack of fault detection capabilities, and inconvenient operation. In particular, they cannot meet the comprehensive requirements of advanced reactors such as thorium-based molten salt reactors for high temperature, high radiation, long stroke, high precision, non-contact absolute measurement, and real-time fault monitoring. Therefore, developing a control rod position measurement scheme that is adaptable to advanced reactor operating conditions, has high measurement accuracy, strong environmental tolerance, and can provide real-time feedback on fault status has become an urgent technical challenge to be solved in this field. Summary of the Invention

[0008] To address the problems of large cumulative errors, lack of real-time fault feedback, and difficulty in achieving both high precision and adaptability to high-temperature and high-irradiation environments in indirect reactor rod position measurements in existing technologies, this invention aims to provide a reactor rod position measurement system.

[0009] The reactor rod position measurement system according to the present invention includes a front-end laser collimation unit, a rear-end laser transceiver unit, and a transmission medium. The front-end laser collimation unit is installed below the control rod deceleration box inside the reactor safety container, opposite to the control rod, and is a purely optical structure without electronic components. The rear-end laser transceiver unit is deployed outside the safety container and is physically isolated from the front-end laser collimation unit through an electrical penetration component. The transmission medium connects the front-end laser collimation unit and the rear-end laser transceiver unit, and is used for transmitting laser signals and receiving echo signals. The rear-end laser transceiver unit includes a rangefinder using the phase-based ranging principle. The front-end laser collimation unit illuminates the control rod surface with a laser beam and obtains the echo signal using the natural diffuse reflection characteristics of the control rod surface, eliminating the need to install a reflector on the end face of the control rod.

[0010] In a preferred embodiment, the front-end laser collimation unit causes the laser beam to irradiate the surface of the control rod at an incident angle of 85° to 95°.

[0011] In a preferred embodiment, the front-end laser collimation unit includes a first collimating lens and a focusing lens that are not parallel to each other, and the back-end laser transceiver unit includes a second collimating lens and a rangefinder. The rangefinder integrates a laser and a photodetector. The laser is used to emit amplitude-modulated continuous wave laser signals, and the photodetector is used to receive echo signals.

[0012] In a preferred embodiment, both the first collimating lens and the focusing lens are antireflective lenses and are able to withstand the temperature and radiation dose inside the reactor safety container.

[0013] In a preferred embodiment, the transmission medium includes an optical fiber capable of withstanding the temperature and radiation dose within the reactor safety container. One end of the optical fiber is connected to the second collimating lens of the back-end laser transceiver unit, and the other end is connected to the first collimating lens of the front-end laser collimating unit, for transmitting emitted laser light.

[0014] In a preferred embodiment, the optical fiber is a multimode optical fiber with a diameter between 50μm and 150μm.

[0015] In a preferred embodiment, the transmission medium further includes an optical fiber bundle that can withstand the temperature and radiation dose inside the reactor safety container. One end of the optical fiber bundle is connected to the focusing lens of the front-end laser collimation unit, and the other end is connected to the second collimating lens of the back-end laser transceiver unit for transmitting diffuse reflection echo signals.

[0016] In a preferred embodiment, the fiber bundle is composed of multiple independent optical fibers arranged in an array with a preset geometric configuration, used to achieve wide-area optical energy acquisition.

[0017] In a preferred embodiment, the fiber bundle has a numerical aperture of 0.21 to 0.23.

[0018] In a preferred embodiment, the signal processing module of the rangefinder is used to analyze the phase difference of the laser round trip to obtain the absolute position of the control rod. When the displacement of the control rod is not greater than a preset displacement threshold within a preset sampling time, or when the sudden change in the phase difference of the echo signal is not less than a preset sudden change value, the signal processing module sends a stop signal to the control rod drive mechanism.

[0019] This invention employs a front-end and back-end separation architecture, deploying the purely optical front-end unit inside the reactor safety container while the back-end unit is isolated and deployed in an external ambient temperature environment. This effectively avoids damage to electronic components from high temperatures and radiation, adapting to complex in-reactor conditions. Combining the phase-based ranging principle with diffuse reflection design, it eliminates the need for reflectors on the control rod end faces, mitigating the risk of reflector failure within the reactor and achieving high-precision absolute position measurement throughout the control rod's entire stroke. Preferably, the combined transmission design of optical fibers and fiber bundles significantly improves optical path coupling efficiency and echo signal collection capability, further ensuring measurement stability and reliability, and meeting the safety and accuracy requirements for reactor rod position measurement. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the reactor rod position measurement system according to the present invention.

[0021] Figure 2 yes Figure 1 A schematic diagram of the front-end laser collimation unit.

[0022] Figure 3 Show Figure 2 The angle between the first collimating lens and the focusing lens.

[0023] Figure 4 yes Figure 1 A schematic diagram of the back-end laser transceiver unit. Detailed Implementation

[0024] The preferred embodiments of the present invention are given below with reference to the accompanying drawings and described in detail.

[0025] like Figure 1 As shown, the reactor rod position measurement system of the present invention is generally divided into a front-end laser collimation unit 100, a rear-end laser transceiver unit 200, and a transmission medium 300. The front-end laser collimation unit 100 is installed in the confined space below the control rod deceleration box inside the reactor safety container, and is connected to the control rod (i.e., Figure 1 The sample is positioned relative to the control rod; the rear laser transceiver unit 200 is deployed outside the safety container and physically isolated from the front laser collimation unit 100 through an electrical penetration device to avoid damage to electronic components from high temperature and radiation; the transmission medium 300 connects the front laser collimation unit 100 and the rear laser transceiver unit 200, transmitting laser signals with low loss, realizing the transmission of laser signals and the reception of echo signals. The laser spot of the front laser collimation unit 100 covers the entire stroke of the control rod (0~4m). The control rod receives the laser and generates a diffuse reflection signal. The rear laser transceiver unit 200 acquires the diffuse reflection echo signal in real time through the transmission medium 300, processes it, and outputs the absolute position information of the control rod.

[0026] The front-end laser collimation unit 100 is a purely optical structure without electronic components, suitable for high-temperature, high-irradiation, and strong-vibration conditions within a safety container. It includes a first collimating lens L1, a focusing lens L2, and a first mounting bracket H1. For example... Figure 2 As shown, the first mounting bracket H1 secures the first collimating lens L1 and the focusing lens L2 together, ensuring the stability of the optical path pointing. To ensure stable reception of diffuse reflection light throughout the entire stroke of the control rod from 0 to 4 m, the first collimating lens L1 and the focusing lens L2 are not parallel but form an angle. In this embodiment, the angle between the first collimating lens L1 and the focusing lens L2 is designed to be 1.42°. Figure 3As shown, this angle design allows the displacement of the laser on the control rod surface to be controlled within 50mm, while the displacement of the reflected light on the focusing lens L2 surface is controlled within 25mm. Furthermore, this non-parallel setup can avoid the 0.5m~1m measurement blind zone of the rangefinder, ensuring that the reflected light signal within a 4m travel range can be effectively collected.

[0027] The back-end laser transceiver unit 200 is the core control and signal processing module, deployed in a normal-temperature environment outside the safety container. It includes a second collimating lens L3, a rangefinder C (integrating laser functionality), and a second mounting bracket H2. For example... Figure 4 As shown, the second mounting bracket H2 fixes the second collimating lens L3 and the rangefinder C into one unit, ensuring the stability of the optical path pointing.

[0028] The transmission medium 300 is a combination of optical fiber G1 and optical fiber bundle G2. One end of optical fiber G1 is connected to the second collimating lens L3 at the rear end, and the other end is connected to the first collimating lens L1 at the front end, used to transmit the laser emitted by the rangefinder C to the front end. One end of optical fiber bundle G2 is connected to the focusing lens L2 at the front end, and the other end is directly connected to the rangefinder, used to transmit the diffuse reflection echo signal of the control rod back to the rear end. In particular, optical fiber bundle G2 is a composite optical waveguide structure, which is formed by bundling multiple independent optical fibers in an array with a preset geometric configuration. Multiple output beams are combined through the optical fiber bundle to form a high-power composite light source, and the large numerical aperture characteristic of the optical fiber bundle is used to realize wide-area light energy acquisition.

[0029] Thus, the optical path of the reactor rod position measurement system of the present invention is as follows: laser emitted by rangefinder C → second collimating lens L3 (beam splitting structure) → optical fiber G1 → first collimating lens L1 → projected onto the control rod; diffuse reflection light from the control rod → focusing lens L2 → optical fiber bundle G2 → transmitted back to rangefinder C, and after processing, the absolute position information of the control rod is output.

[0030] Specifically, the rangefinder C employs a phase-based laser ranging principle. It emits a continuous-wave laser signal with a fixed modulation frequency, using a continuous laser to transmit an amplitude-modulated light signal, while simultaneously using a photodetector to receive the echo signal reflected by a control rod. Due to the laser's round-trip time... It will cause harmonic phase changes The time of flight corresponding to this phase difference is calculated based on the wavelength of the modulated light. This allows for the determination of the target distance R, thus enabling the measurement of the absolute position of the control rod. This principle is compatible with control rod movement speeds of 5~15 mm / s and can achieve a measurement accuracy of ±3 mm within a stroke range of 0~4 m.

[0031] The inventors discovered that interferometric laser ranging relies on changes in the interference fringes of light, making it sensitive to vibrations and temperature fluctuations within the reactor and prone to fringe counting errors. In contrast, the phase method used in this invention calculates distance through phase difference, exhibiting greater tolerance to small vibrations and temperature drifts, making it suitable for strong vibrations and high-temperature conditions within the reactor, and possessing stronger resistance to environmental interference. Furthermore, the range of interferometric laser ranging is typically less than 1m, unable to cover the entire 0-4m travel of the control rods, while the phase method naturally supports long-range measurements without the need for additional range splicing, resulting in better adaptability. Moreover, interferometric laser ranging requires high-precision alignment of the reference and measurement optical paths, which is difficult to achieve in the confined space within the reactor. The phase method used in this invention only needs to ensure the pointing stability of the front collimating mirror, adapting to the simplified installation requirements of a purely optical front-end structure, significantly reducing the complexity of optical path calibration.

[0032] Specifically, since a reflector cannot be installed on the end face of the control rod (high-temperature irradiation causes adhesive failure, molten salt vapor adhesion damages the optical path, and the collimation requirements of the mirror are too high), this invention optimizes the focal length combination of the first collimating mirror L1 and the focusing mirror L2 so that the laser beam illuminates the surface of the control rod at an incident angle of 85°~95°, that is, the laser beam illuminates the surface of the control rod at a vertical angle (±5°). The natural diffuse reflection characteristics of the control rod surface are used to obtain the echo signal. Combined with the large numerical aperture (e.g., 0.22) design of the fiber bundle G2, wide-area optical energy acquisition is achieved.

[0033] Specifically, both the first collimating lens L1 and the focusing lens L2 are adapted to fiber G1 and fiber bundle G2 to avoid attenuation of output power. Simultaneously, their optimized focal lengths jointly address the issues of large output divergence angle and blurred light spots. In a preferred embodiment, both the first collimating lens L1 and the focusing lens L2 are anti-reflection coated lenses. The focusing lens L2 is a 26mm diameter (32.1mm focal length) or 48mm diameter (72.5mm / 90.3mm focal length) anti-reflection coated lens. Both lenses possess high-temperature irradiation resistance, with a high-temperature resistance range of, for example, 110℃~150℃, and a gamma-ray irradiation dose resistance of, for example, 200kGy~1MGy. This means they can withstand the temperature and irradiation dose within the reactor safety container, reducing the reflection light loss of the lenses themselves, improving the coupling efficiency with the transmission medium (fiber G1, fiber bundle G2), and ensuring the signal strength and stability of the diffuse reflection echo signal when directly transmitted to the rangefinder via the fiber bundle G2. In a preferred embodiment, the inner wall of the input port of fiber G1 is blackened, and the output port is changed from the default PC to APC to reduce light reflection from the metal interface and end-face echo interference. In a preferred embodiment, fiber G1 is a high-temperature irradiation-resistant multimode fiber, capable of withstanding the temperature and radiation dose within the reactor safety container. A multimode fiber with a diameter of 50μm-150μm is used, for example, 100μm, achieving a light output efficiency of 69%, low optical path loss, and easy coupling. In a preferred embodiment, fiber bundle G2 is of high-temperature irradiation-resistant specification, capable of withstanding the temperature and radiation dose within the reactor safety container. A 4mm diameter specification is selected, offering low coupling difficulty, a large receiving area, and maximizing echo signal collection. The inventors found that a 6mm diameter fiber bundle is unfavorable for engineering installation due to its large bending radius, while the light intensity difference between 4mm and 2mm is small; therefore, the 4mm specification is preferred. In a preferred embodiment, the ends of fiber bundle G2 are beveled and coated to further suppress end-face echo reflection. In a preferred embodiment, the distance between the focusing lens L2 of the front-end laser collimation unit 100 and the control rod is not less than 50cm. This distance setting can avoid the dead zone of the rangefinder and prevent the light spot from dissipating at close range and affecting the measurement effect.

[0034] The working process of the reactor rod position measurement system of the present invention is briefly described below.

[0035] The laser of the rangefinder C emits a laser beam through fiber G1. After being collimated into a parallel beam by the second collimating lens L3 and the first collimating lens L1, the laser beam illuminates the control rod. The diffuse reflected light from the surface of the control rod is focused by the focusing lens L2 and transmitted to the signal processing module of the rangefinder C. The signal processing module uses the phase method to analyze the phase difference of the laser beam during its round trip and calculates the absolute position of the control rod. If the displacement of the control rod is ≤0.1mm within 5 seconds of continuous sampling (the first preset time, which can be adjusted according to the movement speed of the control rod), or if the phase difference of the echo signal changes abruptly by ≥5°, it is determined to be a fault such as rod jamming or chain jamming, and a stop signal is immediately sent to the control rod drive mechanism.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the invention. Various variations can be made to the above embodiments of the present invention. That is, all simple and equivalent changes and modifications made based on the claims and description of this invention fall within the protection scope of the claims. All aspects not described in detail in this invention are conventional technical content.

Claims

1. A reactor rod position measurement system, characterized in that, The reactor rod position measurement system includes a front-end laser collimation unit, a back-end laser transceiver unit, and a transmission medium; The front-end laser collimation unit is installed below the control rod deceleration box inside the reactor safety container, opposite to the control rod, and is a purely optical structure without electronic components; The back-end laser transceiver unit is deployed outside the safety container and is physically isolated from the front-end laser collimation unit through an electrical penetration component. The transmission medium connects the front-end laser collimation unit and the back-end laser transceiver unit, and is used for transmitting laser signals and receiving echo signals. The back-end laser transceiver unit includes a rangefinder that uses the phase method for ranging. The front-end laser collimation unit illuminates the surface of the control rod with a laser beam and obtains the echo signal by utilizing the natural diffuse reflection characteristics of the control rod surface, without the need to install a reflector on the end face of the control rod.

2. The reactor rod position measurement system according to claim 1, characterized in that, The front-end laser collimation unit causes the laser beam to irradiate the surface of the control rod at an incident angle of 85° to 95°.

3. The reactor rod position measurement system according to claim 1, characterized in that, The front-end laser collimation unit includes a first collimating lens and a focusing lens that are not parallel to each other. The back-end laser transceiver unit includes a second collimating lens and a rangefinder. The rangefinder integrates a laser and a photodetector. The laser is used to emit amplitude-modulated continuous wave laser signals, and the photodetector is used to receive echo signals.

4. The reactor rod position measurement system according to claim 3, characterized in that, Both the first collimating lens and the focusing lens are anti-reflective lenses and are able to withstand the temperature and radiation dose inside the reactor safety container.

5. The reactor rod position measurement system according to claim 3, characterized in that, The transmission medium includes an optical fiber, which can withstand the temperature and radiation dose inside the reactor safety container. One end of the optical fiber is connected to the second collimating lens of the back-end laser transceiver unit, and the other end is connected to the first collimating lens of the front-end laser collimating unit, for transmitting the emitted laser.

6. The reactor rod position measurement system according to claim 5, characterized in that, The optical fiber is a multimode optical fiber with a diameter between 50μm and 150μm.

7. The reactor rod position measurement system according to claim 3, characterized in that, The transmission medium also includes an optical fiber bundle, which is capable of withstanding the temperature and radiation dose inside the reactor safety container. One end of the optical fiber bundle is connected to the focusing lens of the front-end laser collimation unit, and the other end is connected to the second collimation lens of the back-end laser transceiver unit for transmitting diffuse reflection echo signals.

8. The reactor rod position measurement system according to claim 7, characterized in that, The fiber bundle is composed of multiple independent optical fibers arranged in an array with a preset geometric configuration, and is used to realize wide-area optical energy acquisition.

9. The reactor rod position measurement system according to claim 7, characterized in that, The fiber bundle has a numerical aperture of 0.21 to 0.

23.

10. The reactor rod position measurement system according to claim 1, characterized in that, The signal processing module of the rangefinder is used to analyze the phase difference of the laser round trip to obtain the absolute position of the control rod. When the displacement of the control rod is not greater than the preset displacement threshold within a preset sampling time, or when the phase difference of the echo signal changes abruptly, not less than the preset change value, the signal processing module sends a stop signal to the control rod drive mechanism.

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