Leak detection device and method for nuclear power steam generator heat transfer tube

Abstract

This invention discloses a leak detection device and method for heat transfer tubes in nuclear power plant steam generators. The leak detection device includes a probe module, which comprises an infrared laser generating unit, an infrared laser receiving unit, and a hollow optical fiber connected between the infrared laser generating unit and the infrared laser receiving unit. The infrared laser generating unit includes an infrared laser generator and a coupling mirror. The coupling mirror is positioned between the output end of the infrared laser generator and the hollow optical fiber to efficiently couple the infrared laser emitted by the infrared laser generator into the hollow optical fiber. This invention combines a probe module with a hollow optical fiber, utilizing the infrared absorption characteristics of SF6 in the 10.6μm band to achieve highly sensitive leak detection of heat transfer tube leakage rates, resolving the contradiction between small size and long optical path, and meeting the early microcrack monitoring requirements of nuclear power plants.

Description

Technical Field

[0001] This invention relates to the field of tracer gas leak detection technology, and in particular to a leak detection device and method for heat transfer tubes in nuclear power steam generators. Background Technology

[0002] In nuclear power plant operation, the integrity of the steam generator heat transfer tubes is crucial. In the event of a leak, the primary coolant can contaminate the secondary coolant system, leading to radioactive spread or equipment damage. Existing leak detection technologies mainly include: 1. Helium mass spectrometry leak detection: This method requires injecting helium gas into the outside of the heat transfer tube and detecting it with a mass spectrometer. However, the equipment is bulky (probe diameter > 20 mm), complex to operate, and cannot achieve in-situ detection inside the tube. The response time is > 5 minutes, and the lower limit for leak rate detection is only 10%. - 7 Pa·m 3 / s.

[0003] 2. Ultrasonic leak detection: Relies on sound wave reflection, easily affected by noise from the fluid inside the pipe, with a detection limit of approximately 10. -5 Pa·m 3 / s, with a false negative rate of >40% for micron-sized cracks (<1μm).

[0004] 3. Pressure Holding Test: By installing plug flanges at both ends of the heat transfer tube, pressurizing or evacuating the inside of the heat transfer tube, and holding the pressure for a period of time, the pressure drop is checked to determine if there is a leak in the heat transfer tube. The lower limit of detection is approximately 10. -2 Pa·m 3 / s, poor sensitivity, long detection time.

[0005] 4. Traditional infrared leak detection method: mostly used in open environments, limited by short optical path (<0.5m) and large probe size (diameter >25mm), the lower limit of leak rate detection is only 10. -6 Pa·m 3 / s, which cannot be adapted to the inner diameter of the heat transfer tube (typically 19mm). Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide an improved leak detection device and method for heat transfer tubes of nuclear power steam generators.

[0007] The technical solution adopted by the present invention to solve its technical problem is: to provide a leak detection device for heat transfer tubes of nuclear power steam generators, including a probe module, wherein the probe module includes an infrared laser generating unit, an infrared laser receiving unit, and a hollow optical fiber connected between the infrared laser generating unit and the infrared laser receiving unit; The infrared laser generating unit includes an infrared laser generator and a coupling mirror; to match the absorption band of SF6, the infrared laser generator emits an infrared laser with a wavelength of 10.6μm±0.1μm; the coupling mirror is disposed between the output end of the infrared laser generator and the hollow optical fiber, efficiently coupling the infrared laser emitted by the infrared laser generator into the hollow optical fiber; the infrared laser is transmitted by total internal reflection within the hollow optical fiber and finally enters the infrared laser receiving unit; The maximum outer diameter of the probe module is less than 18 mm; the inner diameter of the hollow optical fiber is 0.05 mm to 0.15 mm, and the length is 20 m to 30 m.

[0008] Preferably, the maximum outer diameter of the probe module is 17.6 mm.

[0009] Preferably, the hollow optical fiber has a minimum bending radius of ≥150mm and a transmission loss of <0.5dB / m.

[0010] Preferably, the infrared laser receiving unit includes an infrared laser receiver and a focusing lens, wherein the focusing lens is disposed between the hollow optical fiber and the receiving end of the infrared laser receiver to focus the infrared laser onto the infrared laser receiver.

[0011] Preferably, the probe module further includes a flexible armor structure, which is sleeved on the outside of the hollow optical fiber and connected between the infrared laser generating unit and the infrared laser receiving unit.

[0012] Preferably, the flexible armor structure includes a metal bellows.

[0013] The present invention also provides a method for leak detection of heat transfer tubes in a nuclear power plant steam generator, employing the leak detection device for heat transfer tubes in a nuclear power plant steam generator as described above, the method comprising the following steps: S1. Orient the probe module with the infrared laser generating unit facing and insert it into the heat transfer tube of the nuclear power steam generator until it reaches the target depth inside the heat transfer tube. S2. Inject tracer gas SF6 into the nuclear power steam generator or the secondary loop where the nuclear power steam generator is located; S3. Start the infrared laser generating unit. The infrared laser generating unit emits an infrared laser with a wavelength of 10.6μm±0.1μm. The infrared laser is transmitted to the infrared laser receiving unit by total internal reflection along the hollow optical fiber. S4. Detect the intensity attenuation of the infrared laser received by the infrared laser receiving unit, and analyze the obtained intensity attenuation to determine whether the heat transfer tube is leaking.

[0014] Preferably, in step S1, the probe module enters the heat transfer tube at a speed of 0.05 m / s to 0.2 m / s.

[0015] Preferably, in step S4, the leakage rate of the heat transfer tube is calculated based on the obtained infrared laser intensity attenuation, using the following formula: Where: Q is the leakage rate of the heat transfer tube; L is the optical path length, corresponding to the length of the hollow optical fiber; α is the absorption coefficient of sulfur hexafluoride in the 10.6μm band; V is the internal volume of the heat transfer tube; P is the pressure inside the heat transfer tube; τ≤0.5s is the system response time. Characterizing the degree of infrared laser intensity attenuation, Initial light intensity refers to the reference infrared laser intensity received by the infrared laser receiving unit when no sulfur hexafluoride tracer gas leaks into the heat transfer tube. The infrared laser intensity attenuation refers to the amount of attenuation in the infrared laser intensity received by the infrared laser receiving unit caused by the absorption of some 10.6μm wavelength infrared laser due to the leakage of SF6 tracer gas into the heat transfer tube.

[0016] Preferably, in step S4, when Q ≥ 1.3 × 10 -9 Pa.m 3 A leak in the heat transfer tube is detected when the temperature reaches 0.5°C / s.

[0017] The beneficial effects of this invention are as follows: By combining a probe module with a maximum outer diameter of no more than 18 mm with a hollow optical fiber with a length of up to 24 m, and utilizing the infrared absorption characteristics of SF6 in the 10.6 μm band, the leakage rate of heat transfer tubes in nuclear power steam generators can be detected, achieving a leakage rate detection lower limit of ≤1.3 × 10⁻⁶. -9 Pa·m 3 High-sensitivity leak detection with a response time of ≤0.5 seconds solves the contradiction between small size and long optical path, and meets the monitoring needs of early microcracks (0.01μm level) in nuclear power plants. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a schematic diagram of a leak detection device for a heat transfer tube in a nuclear power steam generator according to an embodiment of the present invention. Detailed Implementation

[0019] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0020] like Figure 1As shown, a leak detection device for the heat transfer tube of a nuclear power steam generator according to an embodiment of the present invention includes an infrared laser generating unit 1, an infrared laser receiving unit 2, and a hollow optical fiber 3 connected between the infrared laser generating unit 1 and the infrared laser receiving unit 2.

[0021] The infrared laser generating unit 1 includes a unit for emitting infrared lasers. The infrared lasers enter the hollow optical fiber 3, are transmitted through total internal reflection in the hollow optical fiber 3, and finally enter the infrared laser receiving unit 2.

[0022] In the probe module, by limiting the size of the infrared laser generating unit 1 (using a small size), the maximum outer diameter of the probe module is less than 18 mm, which is sufficient to allow it to fit into the narrow heat transfer tube 100. In one embodiment, the maximum outer diameter of the probe module is 17.6 mm.

[0023] The infrared laser generating unit 1 may further include an infrared laser generator 10 and a coupling mirror 20. The infrared laser generator 10 is used to emit infrared laser; to match the absorption band of SF6, the infrared laser generator 10 emits infrared laser with a wavelength of 10.6μm±0.1μm. The coupling mirror 20 is disposed between the output end of the infrared laser generator 10 and the hollow optical fiber 3, and is used to efficiently couple the infrared laser into the hollow optical fiber 3.

[0024] The infrared laser generator 10 is preferably ≤Φ8mm in size, such as Φ7.8mm×15mm, and its output power is 3mW.

[0025] The coupling mirror 20 can be a plano-convex lens made of Ge material (focal length 8mm). When the coupling mirror 20 is aligned with the output end of the infrared laser generator 10, the coupling efficiency is ≥92%, reaching 92.5% in a test.

[0026] The inner diameter of the hollow optical fiber 3 is 0.05mm to 0.15mm, preferably 0.1mm. The length of the hollow optical fiber 3 is 20m to 30m, optional but not limited to 24m, which can provide ultra-long optical path for infrared laser transmission.

[0027] Hollow fiber 3 has a hollow fiber structure, consisting of a hollow core and an outer cladding. The outer cladding is made of a material with a refractive index greater than that of air, allowing infrared lasers to propagate via total internal reflection at the air-material interface. Specifically, the outer cladding can be made of fused silica with a refractive index of 1.45 ± 0.05.

[0028] The hollow core of the hollow optical fiber 3 is air (refractive index n1 = 1.0). The outer cladding of the hollow optical fiber 3 can further have a two-layer structure: an inner layer of doped fused silica (refractive index n2 = 1.45) and an outer layer of high-purity silica (refractive index n3 = 1.2). Infrared laser propagation is achieved using the principle of total internal reflection (critical angle ≈ 44°), without the need for coating. That is, the transmission mechanism is: silica refractive index 1.45 > air refractive index 1.0, and the infrared laser propagates at the air-quartz interface in a total internal reflection mode (incident angle > 44°).

[0029] By optimizing the microstructure of the quartz tube in the outer cladding of the hollow optical fiber 3, the minimum bending radius of the hollow optical fiber 3 is ≥150mm, which can adapt to the bending path of the heat transfer tube 100 and ensure that the transmission loss of the hollow optical fiber 3 in the bending path of the heat transfer tube is <0.5dB / m.

[0030] In a bending test of hollow optical fiber 3: with a bending radius of R=150mm, the transmission loss of 24-meter hollow optical fiber 3 is 0.48dB / m, which meets the curvature requirements of nuclear power heat transfer tubes.

[0031] The infrared laser receiving unit 2 may further include an infrared laser receiver 30 and a focusing lens 40. The focusing lens 40 is disposed between the hollow optical fiber 3 and the receiving end of the infrared laser receiver 30, and is used to focus the infrared laser onto the infrared laser receiver 30. The infrared laser receiver 30 is located at the focal point of the focusing lens 40.

[0032] The response time of the infrared laser receiver 30 is ≤0.5 seconds.

[0033] Alternatively, the infrared laser receiver 30 can be a thermopile sensor with a dynamic range of 10. -3 Up to 10 -5 W, response time ≤ 0.1 seconds.

[0034] The focusing lens 40 can be a ZnSe convex lens (focal length 5mm) to focus the infrared laser onto the infrared laser receiver 30 (photosensitive surface Φ0.15mm).

[0035] Furthermore, the probe module also includes a flexible armor structure (not shown), which is fitted over the hollow optical fiber 3 and connected between the infrared laser generating unit 1 and the infrared laser receiving unit 2, providing rigid protection for the hollow optical fiber 3.

[0036] To accommodate the bending of the hollow optical fiber 3 within the heat transfer tube, the flexible armor structure includes a metal bellows, such as a stainless steel bellows.

[0037] The leak detection device for heat transfer tubes of nuclear power steam generators of the present invention is used to detect leaks in heat transfer tubes of nuclear power steam generators using SF6 (sulfur hexafluoride) as a tracer gas.

[0038] refer to Figure 1 The leak detection method for heat transfer tubes in nuclear power steam generators implemented by the leak detection device of the present invention may include the following steps: S1. Position the probe module with the infrared laser generating unit 1 facing it and insert it into the heat transfer tube 100 of the nuclear power steam generator until it reaches the target depth inside the heat transfer tube 100.

[0039] A robot can be used to insert the probe module into the heat transfer tube 100 and advance it within the heat transfer tube 100 until it reaches the target depth. The probe module enters the heat transfer tube 100 at a speed of 0.05 m / s to 0.2 m / s.

[0040] After the probe module enters the heat transfer tube at the target depth of 100, the air inside the hollow optical fiber 3 is also removed by a vacuum pump and other equipment. The vacuum pump and other equipment can be connected to the infrared laser receiver 30 through a three-way connector, so that after the vacuum pump is started, the air inside the hollow optical fiber 3 is extracted through the infrared laser receiver 30.

[0041] S2. Inject tracer gas SF6 into the nuclear power steam generator or the secondary loop where the nuclear power steam generator is located.

[0042] S3. Infrared laser generating unit 1 is started. The infrared laser generator 10 of infrared laser generating unit 1 emits an infrared laser with a wavelength of 10.6μm±0.1μm. The infrared laser is efficiently coupled into the hollow optical fiber 3 through the coupling mirror 20. The infrared laser is transmitted to the infrared laser receiving unit 2 by total internal reflection along the hollow optical fiber 3.

[0043] At the end where the infrared laser receiving unit 2 is located, the infrared laser is first focused by the focusing lens 40, and then enters the infrared laser receiver 30, where it is received.

[0044] S4. Detect the attenuation of the infrared laser intensity received by the infrared laser receiving unit 2, and analyze the obtained infrared laser intensity attenuation to determine whether the heat transfer tube 100 has leaked.

[0045] In step S4, the leakage rate of the heat transfer tube is calculated based on the obtained infrared laser intensity attenuation and the following formula: Where: Q is the leakage rate of the heat transfer tube; L is the optical path length, corresponding to the length of the hollow optical fiber; α is the absorption coefficient of sulfur hexafluoride in the 10.6μm band; V is the internal volume of the heat transfer tube; P is the pressure inside the heat transfer tube; τ≤0.5s is the system response time.

[0046] Characterizes the degree of intensity attenuation (i.e., absorption intensity) of infrared laser light. Initial light intensity refers to the reference infrared laser intensity received by the infrared laser receiving unit when no sulfur hexafluoride (SF6) tracer gas leaks into the heat transfer tube; The infrared laser intensity attenuation refers to the decrease in the intensity of the infrared laser received by the infrared laser receiving unit due to the absorption of a portion of the 10.6μm wavelength infrared laser caused by the leakage of SF6 tracer gas into the heat transfer tube. The difference between the intensity of the light and the intensity after absorption.

[0047] When Q≥1.3×10 -9 Pa.m 3 A leak in heat transfer tube 100 is detected when the temperature reaches 1 / s.

[0048] The leak detection principle of this invention is as follows: Infrared laser light enters hollow optical fiber 3 via coupling mirror 20 and is transmitted through total internal reflection at the air-quartz interface within the fiber 3 (the effective optical path is equal to the length of hollow optical fiber 3, such as 24 meters). If heat transfer tube 100 leaks, SF6 gas seeps into the tube and strongly absorbs infrared laser energy in the 10.6μm wavelength band, causing signal attenuation in infrared laser receiver 30. Therefore, the presence of a leak can be determined by detecting the attenuation of the infrared laser intensity received by infrared laser receiver 30.

[0049] The formula for calculating the leakage rate of the heat transfer tube in this invention is derived from the Lambert-Beer Law in optical gas detection. The law states that the degree of light intensity attenuation is exponentially related to the concentration of the absorbing gas and the optical path length.

[0050] The infrared laser intensity attenuation is the amount of infrared laser intensity attenuation received by the infrared laser receiver 30. Performance. Infrared laser intensity attenuation of infrared laser receiver 30. The relationship between the concentration of the absorbing gas and the optical path length is as follows: = - = (1-e-α·c·L) in, The initial light intensity, The infrared laser intensity received by the infrared laser receiving unit is α, where α is the SF6 absorption coefficient (α≈0.1cm in the 10.6μm band). -1 ·ppm -1 c is the SF6 concentration (vol / vol), L is the optical path (e.g., 24 meters), and e is the natural constant, e≈2.7182818 (the number of decimal places can be selected according to sensitivity requirements).

[0051] Leakage rate Q (Pa·m) of heat transfer tube3 The conversion formula between SF6 concentration (c / s) and SF6 concentration (c) (according to ISO 20485:2010): Q = c·V·P·1 / τ.

[0052] Where V is the internal volume of the heat transfer tube (m³) 3 Typical value: 0.00624m 3 (Inner diameter 19mm, length 22m); P is the internal pressure of the heat transfer tube (Pa), which is atmospheric pressure 101325Pa during leak detection; τ is the system response time (s), in this invention τ≤0.5 s; When L=24 meters, the minimum detectable leakage rate Q min =1.3×10 -9 Pa·m 3 / s.

[0053] In a practical application of this invention, the heat transfer tubes of a steam generator in a nuclear power plant have an inner diameter of 19 mm, a length of 22 m, and a volume V = 0.00624 m³. 3 Leak detection pressure P = 101325 Pa.

[0054] Equipment parameters: outer diameter of probe module 17.6mm, inner diameter of hollow optical fiber 0.1mm, length 24m, response time τ=0.3s.

[0055] Detection results: SF6 concentration detected: c = 8 × 10⁻⁶ -13 vol / vol.

[0056] Converted to leakage rate Q: Q=(8×10 -13 )×0.00624×101325×10.3=1.68×10 -9 Pa·m 3 / s.

[0057] Minimum detectable leakage rate measured: 1.7 × 10⁻⁶ -9 Pa·m 3 / s (satisfying ≤1.3×10 -9 Pa·m 3 / s design goals).

[0058] Bending test: When the heat transfer tube is advanced through 3 bending points (R=180mm), the transmission loss of the hollow optical fiber is stable at 0.45dB / m.

[0059] In summary, this invention has the following advantages (taking a 24-meter hollow optical fiber as an example): Ultra-high sensitivity: A 24-meter optical path combined with a fast response (τ≤0.5 s) achieves a lower limit for leak rate detection ≤1.3×10⁻⁶. -9 Pa·m3 / s (capable of detecting cracks up to 0.01 μm), compared to existing technologies (helium mass spectrometry lower limit 10). -7 Pa·m 3 / s) increased by 77 times, far exceeding the nuclear power safety threshold (10 -7 Pa·m 3 / s).

[0060] Rapid and accurate positioning: The probe module is directly inserted into the pipe, and the signal response time is ≤0.5 seconds; continuous detection over 24 meters can accurately locate the leak point (resolution ±5cm).

[0061] Breakthrough in size: The 17.6mm diameter probe module is compatible with all nuclear power heat transfer tubes (inner diameter 15~25mm), and the 0.1mm inner diameter hollow optical fiber achieves 24-meter low-loss transmission (bending loss <0.5dB / m) through total internal reflection mechanism.

[0062] Nuclear power applicability: The all-optical structure eliminates the risk of electrical sparks, and the flexible design supports automatic robot propulsion, making it suitable for high-radiation environments.

[0063] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A leak detection device for heat transfer tubes in a nuclear power plant steam generator, characterized in that, The probe module includes an infrared laser generating unit, an infrared laser receiving unit, and a hollow optical fiber connected between the infrared laser generating unit and the infrared laser receiving unit. The infrared laser generating unit includes an infrared laser generator and a coupling mirror; to match the absorption band of SF6, the infrared laser generator emits an infrared laser with a wavelength of 10.6μm±0.1μm; the coupling mirror is disposed between the output end of the infrared laser generator and the hollow optical fiber, efficiently coupling the infrared laser emitted by the infrared laser generator into the hollow optical fiber; the infrared laser is transmitted by total internal reflection within the hollow optical fiber and finally enters the infrared laser receiving unit; The maximum outer diameter of the probe module is less than 18 mm; the inner diameter of the hollow optical fiber is 0.05 mm to 0.15 mm, and the length is 20 m to 30 m.

2. The nuclear power steam generator leak detection apparatus of claim 1, wherein, The maximum outer diameter of the probe module is 17.6 mm.

3. The nuclear power steam generator leak detection apparatus of claim 1, wherein, The hollow optical fiber has a minimum bending radius of ≥150mm and a transmission loss of <0.5dB / m.

4. The nuclear power steam generator leak detection apparatus of claim 1, wherein, The infrared laser receiving unit includes an infrared laser receiver and a focusing lens. The focusing lens is disposed between the hollow optical fiber and the receiving end of the infrared laser receiver to focus the infrared laser onto the infrared laser receiver.

5. The nuclear power steam generator leak detection apparatus of any one of claims 1-4, wherein, The probe module also includes a flexible armor structure, which is sleeved on the outside of the hollow optical fiber and connected between the infrared laser generating unit and the infrared laser receiving unit.

6. The nuclear power steam generator leak detection apparatus of claim 5, wherein, The flexible armor structure includes a metal bellows.

7. A method of inspecting a nuclear power steam generator heat transfer tube for leaks, the method comprising: The leak detection device for the heat transfer tubes of a nuclear power steam generator according to any one of claims 1-6, and the leak detection method for the heat transfer tubes of a nuclear power steam generator, include the following steps: S1. Orient the probe module toward the heat transfer tube of the nuclear power steam generator with the infrared laser generating unit facing it, until it reaches the target depth inside the heat transfer tube. S2. Inject tracer gas SF6 into the nuclear power steam generator or the secondary loop where the nuclear power steam generator is located; S3. Start the infrared laser generating unit. The infrared laser generating unit emits an infrared laser with a wavelength of 10.6μm±0.1μm. The infrared laser is transmitted to the infrared laser receiving unit by total internal reflection along the hollow optical fiber. S4. Detect the attenuation of the infrared laser intensity received by the infrared laser receiving unit, and analyze and determine whether the heat transfer tube is leaking based on the obtained infrared laser intensity attenuation.

8. The nuclear power steam generator leak detection method of claim 7, wherein, In step S1, the probe module enters the heat transfer tube at a speed of 0.05 m / s to 0.2 m / s.

9. The nuclear power steam generator leak detection method of claim 7, wherein, In step S4, the leakage rate of the heat transfer tube is calculated based on the obtained infrared laser intensity attenuation and the following formula: Where: Q is the leakage rate of the heat transfer tube; L is the optical path length, corresponding to the length of the hollow optical fiber; α is the absorption coefficient of sulfur hexafluoride in the 10.6μm band; V is the internal volume of the heat transfer tube; P is the pressure inside the heat transfer tube; τ≤0.5s is the system response time. Characterizing the degree of infrared laser intensity attenuation, Initial light intensity refers to the reference infrared laser intensity received by the infrared laser receiving unit when no sulfur hexafluoride tracer gas leaks into the heat transfer tube. The infrared laser intensity attenuation refers to the amount of attenuation in the infrared laser intensity received by the infrared laser receiving unit caused by the absorption of some 10.6μm wavelength infrared laser due to the leakage of SF6 tracer gas into the heat transfer tube.

10. The nuclear power steam generator leak detection method of claim 9, wherein, In step S4, when Q ≥ 1.3 x 10 -9 Pa.m³ / s, it is determined that the heat transfer tube leaks.

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