A local heating type single fuel rod high-temperature helium leak detection device and method

Abstract

The present invention provides a high-temperature helium leak detection method, which uses the method of local heating of the weld (different from the overall heating of the fuel rod) for heating. One fuel rod is placed in one leak detection chamber, and the leak detection of the fuel rod is carried out under the conditions that the ultimate vacuum degree is 5×10-4 Pa and the heating temperature is within 600 °C. The method is designed with a heating system, a temperature measurement system, and an air-cooling temperature reduction system. The heating adopts the way of electric heating wire outside the vacuum chamber or induction heating, the temperature reduction adopts the way of flowing compressed air air-cooling outside the vacuum chamber, and the temperature monitoring adopts direct monitoring by thermocouple. A single detection can be completed within 30 minutes.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature helium mass spectrometry leak detection (hereinafter referred to as high-temperature helium leak detection), and particularly relates to a device and method for helium leak detection after locally heating the weld of a fuel rod. Background Technique

[0002] In nuclear fuel production, some nuclear fuel rods need to be subjected to helium leak detection at high temperatures to simulate whether the seal of the fuel rod meets the requirements under the operating conditions of the reactor, and the temperature during leak detection needs to reach 500°C.

[0003] In the conventional detection of high-temperature helium leak detection, first, the fuel rod is placed in a container, the container is evacuated and then heated, and helium leak detection is carried out after heating to the target temperature. The current helium leak detection methods have the following problems: 1) After heating multiple fuel rods (generally within 6) to the target temperature as a whole for helium leak detection, this method uses an external heating method outside the vacuum chamber, greatly increasing the volume of the vacuum chamber, and the heating, evacuation, and cooling times are very long. Only one high-temperature helium leak detection can be completed in one working day; 2) If more fuel rods are simultaneously subjected to high-temperature helium leak detection, at high temperatures, the fuel rods release adsorbed gases, making the background leak rate of the leak detection system much greater than the allowable leak rate of the fuel rod, and leak detection cannot be carried out. 3) Since the vacuum chamber is also made by welding, a water cooling structure must be added to the weld at the outer wall of the vacuum chamber to control the temperature of this part. At the same time, to prevent excessive deformation of the door frame and door panel, water cooling structures are also provided at the vacuum flange gasket of the door frame and on both sides of the door panel. The leak detection system is bulky and has a low intrinsic safety level. 4) Some methods use a nitrogen circulation heating method for high-temperature helium leak detection, and the helium leak detection temperature is 230 - 270°C, which is relatively low and cannot reach the required 500°C of the fuel rod.

[0004] To improve work efficiency, reduce the heating and evacuation time of high-temperature helium leak detection, and enhance the intrinsic safety level of the high-temperature leak detection system, a method of locally heating a single fuel rod is adopted for high-temperature helium leak detection. A locally heated single fuel rod high-temperature helium leak detection device and method are invented. Summary of the Invention

[0005] The main purpose of the present invention is to provide a high-temperature helium leak detection device and method for locally heating a single fuel rod, which can effectively solve the problems in the background technique.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is: A locally heated single fuel rod high-temperature helium leak detection device, with temperature control device A and temperature control device B distributed at both ends of the leak detection chamber. The leak detection chamber is divided into left and right parts. On the left side, there are standard leak hole system interface A, standard leak hole system interface B, vacuum pump group system interface, and helium leak detector system interface; a sealing flange is installed on the right side of the leak detection chamber, and the fuel rod to be detected is placed in the leak detection chamber.

[0007] The temperature control device A and the temperature control device B have exactly the same structure.

[0008] The temperature control device A includes a left end cover, a cylinder body, and a right end cover. A thermocouple is installed on the left end cover, and there is a heating mechanism in the leak detection chamber. There are an air outlet channel and an air inlet channel at the lower part of the cylinder body, and there is heat insulation cotton inside the cylinder body.

[0009] The nut fixes the end cover and cooperates with the hollow screw to fix the thermocouple. The thermocouple chamber places the thermocouple to measure the temperature, which is separated from the inside of the leak detection chamber by the leak detection chamber end cover. The fuel rod is placed inside the leak detection chamber.

[0010] The leak detection chamber end cover is sealed by welding.

[0011] A support device is installed at the lower part of the leak detection chamber.

[0012] A sliding guide rail is installed at the lower end of the temperature control device B.

[0013] A high-temperature helium leak detection method for a single fuel rod with local heating includes the following steps:

[0014] S1: Open the fastening bolts on the sealing flange, move the right half of the leak detection chamber, and leave a space for the fuel rod to be loaded into the leak detection chamber;

[0015] S2: Put the fuel rod into the leak detection chamber;

[0016] S3: Reseal the leak detection chamber;

[0017] S4: Connect the vacuum pump group through the system interface and evacuate the leak detection chamber;

[0018] S5: Heat through the temperature control device A and the temperature control device B, and perform real-time temperature measurement through the temperature measurement device;

[0019] S6: After reaching the leak detection temperature, connect the leak detection chamber through the standard leak hole system interface A and the standard leak hole system interface B, calibrate the leak detection system, and verify the sensitivity of the system;

[0020] S7: Close the vacuum pump group, open the helium leak detector system interface, and perform high-temperature helium leak detection;

[0021] S8: After the leak detection is completed, close the helium leak detector system interface, open the compressed air inlet channel and the compressed air outlet channel, and cool down the equipment;

[0022] S9: After the cooling is completed, take out the detected fuel rod and perform the next cycle operation.

[0023] In the above S4, the vacuum of the leak detection chamber is less than 10 Pa.

[0024] In S5, the temperature is measured in real time through a temperature measuring device, and the temperatures at both ends of the fuel rod are observed. The next operation can only be carried out when the temperatures reach 500 °C.

[0025] In S8, compressed air is used to cool down the equipment.

[0026] Cool down to below 50 °C.

[0027] The remarkable effects of the present invention are as follows:

[0028] (1) After locally heating the circumferential weld of the fuel rod, high-temperature helium leak detection is carried out in the present invention. A cycle is completed within 30 minutes, greatly reducing the heating-up time, vacuum pumping time, and cooling-down time, and improving the detection efficiency.

[0029] (2) The present invention uses a small chamber to conduct high-temperature helium leak detection on a single fuel rod. The detection process is no longer affected by the gas adsorbed by the fuel rod itself, ensuring the accuracy of the detection data.

[0030] (3) Through the design of the leak detection small chamber and the local heating structure in the present invention, there is no need to add a water cooling mechanism outside the leak detection chamber, improving the inherent safety of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic structural diagram of the present invention;

[0032] Figure 2 For the present invention Figure 1 The enlarged view of the structure at A in the figure.

[0033] Figure 3 For the present invention Figure 2 The enlarged view of the structure at B in the figure.

[0034] In the figure:

[0035] 1 Temperature control device A (with the same internal structure as 8); 2 Standard leak hole system interface A; 3 Standard leak hole system interface B; 4 Vacuum pump group system interface; 5 Helium leak detector system interface; 6 Leak detection chamber; 7 Sealing flange; 8 Temperature control device B, 9 Sliding guide rail; 10 Support device; 11 Thermocouple; 12 Left end cover; 13 Cylinder body; 14 Heating mechanism; 15 Right end cover; 16 Compressed air outlet channel; 17 Compressed air inlet channel; 18 Heat insulation cotton; 19 Nut; 20 Thermocouple fixed end cover; 21 Thermocouple chamber; 22 Leak detection chamber end cover; 23 Fuel rod; 24 Inside the leak detection chamber; 25 Hollow screw; DETAILED DESCRIPTION OF THE INVENTION

[0036] A locally heated high-temperature helium leak detection device for a single fuel rod, as Figure 1As shown in the figure, the temperature control device A1 and the temperature control device B8 are distributed at both ends of the leak detection chamber 6 to realize the heating, cooling and temperature monitoring of the circumferential welds at both ends of the fuel rod 23. The heating is carried out by means of electric heating wires outside the vacuum chamber or induction heating, the cooling is carried out by means of flowing compressed air for air cooling outside the vacuum chamber, and the temperature monitoring is directly carried out by thermocouples. The leak detection chamber 6 is divided into two parts on the left and right. On the left side, there are a standard leak hole system interface A2, a standard leak hole system interface B3, a vacuum pump group system interface 4, and a helium leak detector system interface 5. The standard leak hole system interface A2 and the standard leak hole system interface B3 realize the system calibration and verification functions. The system interface 4 is used to connect the vacuum pump group to make the leak detection chamber reach a vacuum environment. The system interface 5 is used to connect the helium leak detector to detect the system background and the leak rate of the fuel rod. The leak detection chamber 6 places the fuel rod 23 to be detected. The reference dimensions are: the inner diameter is 10 mm larger than the outer diameter of the fuel rod 23, and the length is 40 mm longer than the total length of the fuel rod to prevent the fuel rod from being bumped when it is loaded and unloaded. A sealing flange 7 is installed on the right side of the leak detection chamber 6. The sealing flange 7 realizes the sealing of the leak detection chamber 6. A support device 10 is installed at the lower part of the leak detection chamber 6, and a sliding guide 9 is installed at the lower end of the temperature control device B8. The sliding guide 9 is used to move the temperature control device left and right when loading and unloading the fuel rod. The support device 10 is used to support and fasten the helium leak detection device.

[0037] Figure 2 It is the internal structure diagram of the temperature control device A1. The temperature control device A1 and the temperature control device B8 have exactly the same structure, including a left end cover 12, a cylinder body 13, and a right end cover 15. A thermocouple 11 is installed on the left end cover 12 to realize temperature monitoring. There is a heating mechanism 14 on the leak detection chamber 6 to realize the heating function (either electric heating wires or induction heating is acceptable). There are an air outlet channel 16 and an air inlet channel 17 at the lower part of the cylinder body 13. The air outlet channel 16 and the air inlet channel 17 are used for rapid cooling with compressed air after the detection. There is a heat preservation cotton 18 inside the cylinder body 13 to realize the temperature transfer and the support and fixation of the heating mechanism.

[0038] Figure 3 It is the internal schematic diagram of the leak detection chamber 6. Among them, a nut 19 is fixed on the end cover 20 and cooperates with a hollow screw 25 to realize the fixation of the thermocouple 11. The thermocouple chamber 21 places the thermocouple 11 to measure the temperature. It is separated from the leak detection chamber 24 by a leak detection chamber end cover 22. Since the heating mechanism heats the whole in the temperature control device, the temperature of the thermocouple chamber is the same as that of the end part of the leak detection chamber (the fuel rod weld area). The leak detection chamber end cover 22 is completely sealed and welded to ensure the vacuum degree of the leak detection chamber. The fuel rod 23 is the workpiece to be detected and is placed inside the leak detection chamber 24.

[0039] The weld is generally about 10 mm at the end.

[0040] A method for a high-temperature helium leak detection device for a single fuel rod with local heating, comprising the following steps:

[0041] S1: Open the fastening bolts on the sealing flange 7, move the right half of the leak detection chamber 6, and leave a space for the fuel rod to be inserted into the leak detection chamber 6;

[0042] S2: Place the fuel rod 23 to be detected into the leak detection chamber 6, and pay attention not to cause bumps during the operation process;

[0043] S3: Operate in the reverse process of S1 to reseal the leak detection chamber 6;

[0044] S4: Connect the vacuum pump group through the system interface 4 to evacuate the leak detection chamber 6;

[0045] S5: Heat through the temperature control device A1 and the temperature control device B8, and perform real-time temperature measurement through the temperature measuring device 11;

[0046] S6: After reaching the leak detection temperature, connect the leak detection chamber 6 through the standard leak hole system interface A2 and the standard leak hole system interface B3, calibrate the leak detection system, and verify the sensitivity of the system;

[0047] S7: Close the vacuum pump group, open the helium leak detector system interface 5, and perform high-temperature helium leak detection;

[0048] S8: After the leak detection is completed, close the helium leak detector system interface 5, open the compressed air inlet channel 17 and the compressed air outlet channel 16 to cool down the equipment;

[0049] S9: After the cooling is completed, take out the detected fuel rod 23 and perform the next cycle operation.

[0050] In S3, before tightening the bolts of the sealing flange 7, the flange openings should be completely aligned, and tightened one by one according to the method of symmetric tightening to ensure the sealing performance;

[0051] In S4, the vacuum degree of the leak detection chamber 6 should be pumped down to at least below 10 Pa before the next operation can be carried out;

[0052] In S5, through the temperature measuring device 11 for real-time temperature measurement, observe the temperatures of the welds at both ends of the fuel rod, and only when both reach 500 °C can the next operation be carried out;

[0053] In S8, use compressed air to cool down the equipment, and only when the temperature is cooled down to below 50 °C can the next operation be carried out.

Claims

1. A local heating type single fuel rod high-temperature helium leak detection device, characterized in that: The temperature control device A (1) and the temperature control device B (8) are distributed at both ends of the leak detection chamber (6). The leak detection chamber (6) is divided into two parts on the left and right. On the left side, there are a standard leak hole system interface A (2), a standard leak hole system interface B (3), a vacuum pump group system interface (4), and a helium leak detector system interface (5); on the right side of the leak detection chamber (6), a sealing flange (7) is installed, and the fuel rod (23) to be detected is placed in the leak detection chamber (6); The temperature control device A (1) and the temperature control device B (8) have exactly the same structure; The temperature control device A (1) includes a left end cover (12), a cylinder body (13), and a right end cover (15). A thermocouple (11) is installed on the left end cover (12), and there is a heating mechanism (14) on the leak detection chamber (6). There are an air outlet channel (16) and an air inlet channel (17) at the lower part of the cylinder body (13), and there is heat insulation cotton (18) inside the cylinder body (13); The nut (19) is fixed on the thermocouple fixed end cover (20) and cooperates with the hollow screw (25) to fix the thermocouple (11). The thermocouple chamber (21) is used to place the thermocouple to measure the temperature, and it is separated from the inside of the leak detection chamber (24) by the leak detection chamber end cover (22). The fuel rod (23) is placed inside the leak detection chamber (24); The leak detection chamber end cover (22) is sealed and welded; A support device (10) is installed at the lower part of the leak detection chamber (6); A sliding guide rail (9) is installed at the lower end of the temperature control device B (8).

2. A method of applying a local heating type single fuel rod high-temperature helium leak detection device as described in claim 1, characterized in that: It includes the following steps: S1: Open the fastening bolts on the sealing flange (7), move the right half of the leak detection chamber (6), and leave a space for loading the fuel rod into the leak detection chamber (6); S2: Place the fuel rod (23) into the leak detection chamber (6); S3: Re-seal the leak detection chamber (6); S4: Connect the vacuum pump group through the vacuum pump group system interface (4) to evacuate the leak detection chamber (6); S5: Heat through the temperature control device A (1) and the temperature control device B (8), and perform real-time temperature measurement through the temperature measurement device; S6: After reaching the leak detection temperature, connect the leak detection chamber (6) through the standard leak hole system interface A (2) and the standard leak hole system interface B (3), calibrate the leak detection system, and verify the sensitivity of the system; S7: Close the vacuum pump group, open the helium leak detector system interface (5), and perform high-temperature helium leak detection; S8: After the leak detection is completed, close the helium leak detector system interface (5), open the compressed air inlet channel (17) and the compressed air outlet channel (16) to cool down the equipment; S9: After cooling down, take out the detected fuel rod (23) and perform the next cycle operation.

3. According to the method described in claim 2, characterized in that: In step S4, the vacuum in the leak detection chamber (6) is less than 10 Pa.

4. According to the method described in claim 2, characterized in that: In S5, the temperature is measured in real time through a temperature measuring device, and the temperatures at both ends of the fuel rod (23) are observed. Only when both temperatures reach 500 °C can the next operation be carried out.

5. The method according to claim 2, wherein: in S8, compressed air is used to cool down the equipment.

6. The method according to claim 5, wherein: the temperature is cooled down to below 50 °C.

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