A test method for the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant

Abstract

This application belongs to the field of nuclear power plant primary loop sealing technology, specifically relating to a test method for the main seal of the reactor pressure vessel of a nuclear power plant VVER unit. The method includes: Step S1, simulating the deformation of the sealing structure through multi-material staged extrusion, with a helium leakage rate test performed after each simulation, followed by a hydrostatic test at the maximum deformation value of the V-groove of the cylinder to obtain the maximum critical defect; the sealing structure consists of a pressure vessel, a pressure vessel top cover, and a pure nickel sealing ring; Step S2, comprehensively calibrating the deformation of the V-groove of the cylinder and the sealing plane of the top cover using the steel ball protrusion. This application solves the technical problem of simulating and measuring the plastic deformation of the main sealing structure of the reactor pressure vessel in a nuclear power plant VVER unit by simulating the deformation of the sealing structure through multi-material staged extrusion and comprehensively calibrating the deformation using the steel ball protrusion.

Description

Technical Field

[0001] This application belongs to the field of nuclear power plant primary loop sealing technology, specifically relating to a test method for the main seal of the reactor pressure vessel of a nuclear power plant VVER unit. Background Technology

[0002] Patent 1 (Application No.: 201911242199.8) discloses a method for sealing detection during pneumatic testing of large pressure vessels, comprising the following steps: 1) Pressurizing the pressure vessel and locating leaks; 2) Continuing to pressurize the pressure vessel based on step 1) and locating leaks; 3) During the pressurization of the pressure vessel to approximately the design pressure, continuously monitoring the helium background of relevant compartments and rooms. If the helium background is abnormally elevated, investigate potential leaks in valves, flanges, welds, etc., within the corresponding compartment / room; 4) When the pressure is increased to the test pressure and then decreased to the design pressure, leaks are identified through routine inspections. This invention ensures that the airtightness of large pressure vessels in high-temperature gas-cooled reactor nuclear power plants meets requirements, keeping the overall leakage rate within a reasonable range.

[0003] Although patent 1 can be used for air pressure testing and sealing detection of large pressure vessels, it conducts sealing tests on the equipment body, but it cannot measure the limit deformation of the cylinder V-shaped sealing groove and the top cover sealing plane, or predict the sealing performance under the limit deformation.

[0004] Patent 2 (Application No.: 202011231810.X) relates to an online monitoring method for the sealing status of an O-ring seal in a nuclear reactor pressure vessel, belonging to the field of leakage monitoring. The method involves: utilizing the correspondence between the sealing status of the O-ring seal and its elastic deformation, as well as the structural gap H between the upper and lower flange sealing surfaces; assessing the sealing status of the O-ring seal by monitoring the structural gap H between the upper and lower flange sealing surfaces; setting measuring points at symmetrical fastening bolts along the circumference of the O-ring seal; using a fiber optic probe inserted into the structural gap between the upper and lower flange sealing surfaces at the fastening bolt measuring points to obtain information about the structural gap H; employing laser frequency scanning interferometry to achieve high-precision measurement of the micron-level structural gap change ΔH; and evaluating the sealing status of the O-ring seal accordingly, thereby transforming the monitoring of the pressure vessel's leakage status into real-time online monitoring of the sealing status, and changing post-leak alarms into pre-leak warnings.

[0005] Although patent 2 can be used for online monitoring of the sealing status of the O-ring seal in a nuclear reactor pressure vessel, it only detects the sealing status and elastic deformation of the sealing ring, and does not detect the plastic deformation of the V-shaped sealing groove of the pressure vessel cylinder and the sealing plane of the top cover. Summary of the Invention

[0006] In view of this, this application provides a test method for the main seal of the reactor pressure vessel of a nuclear power plant VVER unit. The method simulates the deformation of the sealing structure by multi-material staged extrusion and uses the amount of steel ball protrusion to comprehensively calibrate the deformation, so as to solve the technical problems of simulating and measuring the plastic deformation of the main sealing structure (V-groove and sealing plane) of the reactor pressure vessel of a nuclear power plant VVER unit.

[0007] This application provides a method for testing the main seal of the reactor pressure vessel of a VVER (Vehicle Verification Unit) nuclear power plant unit, which includes:

[0008] Step S1: Multi-material staged extrusion simulation of the deformation of the sealing structure, and after each simulation, helium leakage rate test is performed first, and then hydrostatic test is performed at the maximum value of the V-groove deformation of the cylinder to obtain the maximum critical defect; the sealing structure consists of a pressure vessel, a pressure vessel top cover and a pure nickel sealing ring;

[0009] Step S2: Use the steel ball protrusion to comprehensively calibrate the deformation of the cylinder V-groove and the sealing plane of the top cover.

[0010] In one specific embodiment of this application, step S2 includes:

[0011] Step S21: Place a standard steel ball with a diameter of 5mm in the V-groove of the cylinder, and measure the amount of the standard steel ball protruding from the plane of the V-groove. The measurement result is the deformation of the V-groove of the cylinder and the sealing plane of the top cover.

[0012] In one specific embodiment of this application, step S21 includes:

[0013] Step S211: Place the support block on the flat surface and place the standard steel ball into the through hole of the support block.

[0014] Step S212: Place a depth micrometer on the support block and measure the distance from the top of the standard steel ball to the upper surface of the support block. Finally, calculate the protrusion of the standard steel ball from the plane containing the V-groove. Protrusion = Support block thickness - Distance from the top of the standard steel ball to the upper surface of the support block.

[0015] In one specific embodiment of this application, step S1 includes:

[0016] Step S11: The deformation is simulated sequentially using N6 pure nickel ring, stainless steel wire, and alloy steel wire. After each simulation, the helium leakage rate is tested first, and then a water pressure test is conducted at the maximum deformation value of the V-groove of the cylinder.

[0017] Step S12: If the water pressure test passes, the maximum value of the set cylinder V-shaped groove deformation is considered to be the maximum critical defect.

[0018] Step S13: If the hydrostatic test fails, reduce the maximum value of the V-shaped groove deformation of the cylinder and repeat the helium leakage rate test and hydrostatic test until the hydrostatic test passes, and find the maximum critical defect of the hydrostatic test.

[0019] In one specific embodiment of this application, the helium leakage rate test in step S1 is carried out using the vacuum method. Under the maximum load, at a pressure difference of 0.1 MPa and a temperature of room temperature, the helium leakage rate is recorded.

[0020] In one specific embodiment of this application, the pressure of the water pressure test in step S1 is 30 MPa abs, the temperature is room temperature, and the pressure holding time is not less than 30 min.

[0021] In one specific embodiment of this application, the water pressure test in step S1 is to measure the pressure in the test chamber using a pressure gauge, with the range of the pressure gauge controlled at 1.5 to 2 times the test pressure.

[0022] In one specific embodiment of this application, the main seal test method for the reactor pressure vessel of the VVER unit of the nuclear power plant further includes:

[0023] Step S3: Supplementary test. Based on the results of the simulation test of the deformation of the sealing structure, select the limit dimensions of the V-groove of the cylinder and the sealing plane of the top cover, and use these as the object to conduct a sealing performance test.

[0024] In one specific embodiment of this application, the sealing performance test in step S3 includes a helium leakage rate test. The helium leakage rate test is conducted under the conditions of maximum load, at a pressure difference of 0.1 MPa, and at 350°C, and the helium leakage rate is recorded.

[0025] In one specific embodiment of this application, the sealing performance test in step S3 includes a hydrostatic test. The conditions for the hydrostatic test are a test pressure of 17.6 MPa abs, a test temperature of 350°C, and a pressure holding time of not less than 30 min.

[0026] The beneficial effects of this technical solution are: it can not only simulate the ultimate deformation of the V-shaped sealing groove of the cylinder and the sealing plane of the top cover, but also evaluate the sealing performance under this deformation. By using multiple materials in batches under different clamping forces, the deformation trend of the V-shaped sealing groove of the pressure vessel cylinder and the sealing plane of the top cover are measured and the sealing safety is evaluated. Attached Figure Description

[0027] Figure 1 The diagram shows a sealing configuration of a VVER reactor pressure vessel using a V-groove and a pure nickel sealing ring.

[0028] Figure 2The diagram shown is a flowchart illustrating a method for testing the main seal of a reactor pressure vessel in a nuclear power plant VVER unit, according to an embodiment of this application.

[0029] Figure 3 The diagram shows a schematic of a reactor pressure vessel main seal test procedure according to an embodiment of this application.

[0030] Figure 4 The diagram shown is a schematic diagram of an indirect measurement fixture for the deformation of a sealed structure provided in an embodiment of this application.

[0031] Figure 5 The diagram shown is a schematic diagram of a sealing structure deformation simulation tooling provided in an embodiment of this application.

[0032] Figure 6 The diagram shown is a schematic diagram of a helium leak test system provided in an embodiment of this application.

[0033] Figure 7 The diagram shown is a schematic diagram of a hydrostatic testing system provided in an embodiment of this application. Detailed Implementation

[0034] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0035] The main seal of the reactor pressure vessel in a VVER (Vehicle Vernier Regulator) unit of a nuclear power plant uses a V-groove and pure nickel sealing ring for sealing. Figure 1 As shown, the pressure vessel's base material is alloy steel with a stainless steel overlay layer. The pressure vessel's top cover has a sealing plane, and the pressure vessel cylinder has a V-shaped sealing groove (located within the stainless steel overlay layer). The pure nickel sealing ring has a solid circular cross-section with a diameter of 5 mm. During reactor operation, under high temperature, high pressure, and main bolt preload, the continuous compression of the pure nickel sealing ring against the cylinder's V-shaped sealing groove and the top cover's sealing plane causes plastic deformation in these areas. This plastic deformation tends to expand continuously with increasing refueling cycles. To investigate the limiting deformation of this plastic deformation and the sealing safety under this deformation, with the pure nickel sealing ring diameter remaining constant, this study aims to determine the optimal parameters.

[0036] To investigate the deformation trend and ultimate deformation dimensions of the V-shaped sealing groove and the sealing plane of the top cover, as well as the sealing safety under the ultimate deformation dimensions, an experimental approach was adopted. During the experiment, it was necessary to accurately, economically, and quickly simulate the plastic deformation, and also to measure the deformation using feasible measurement methods.

[0037] This application provides at least one embodiment of a method for testing the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant, referencing... Figure 2 and Figure 3 The main seal test method for the reactor pressure vessel of the VVER unit of the nuclear power plant includes the following steps.

[0038] Step S1 involves simulating the deformation of the sealing structure through multi-material staged extrusion. After each simulation, a helium leakage rate test is performed, followed by a hydrostatic test at the maximum value of the V-groove deformation of the cylinder to obtain the maximum critical defect. The sealing structure consists of a pressure vessel, a pressure vessel top cover, and a pure nickel sealing ring.

[0039] In some embodiments, the cross-sectional dimension of the pure nickel sealing ring is 5 mm. The pressure vessel top cover has a sealing plane, and the pressure vessel cylinder has a V-groove (the V-groove is located in the stainless steel weld overlay layer).

[0040] It should be noted that the V-groove can also be called a V-shaped sealing groove.

[0041] For example, the base material of the pressure vessel is alloy steel 15X2HMФA-A, and the surface is overlaid with two layers of stainless steel. The first layer is made of C. B -07X25H13, the second layer material is C. B- 04X20H10Г2Б.

[0042] Under the long-term action of high temperature, high pressure, and preload of the main bolts, the sealing structure undergoes plastic deformation of the cylinder V-shaped sealing groove and the top cover sealing plane under the compression of the pure nickel sealing ring. To simulate the deformation of the sealing structure under long-term high temperature and high pressure, considering the economy of the experiment and the fact that the deformation of the cylinder V-shaped sealing groove and the top cover sealing plane should be closer to the deformation in actual engineering, a simulated sealing ring of various materials with progressive strength and hardness was used. The sealing structure (V-shaped groove and sealing plane) was compressed in stages to simulate the deformation. First, an N6 pure nickel ring was used for the compression test, then a stainless steel wire was used for the sealing test, and finally an alloy steel wire was used for the sealing test. After each test, the deformation of the cylinder V-shaped sealing groove and the top cover sealing plane was measured until the deformation of the cylinder V-shaped sealing groove and the top cover sealing plane no longer increased. Finally, a helium detection test, a hydrostatic test, and a thermal cycling test were conducted.

[0043] Step S2: Use the steel ball protrusion to comprehensively calibrate the deformation of the cylinder V-groove and the sealing plane of the top cover.

[0044] The deformation of the V-groove in the cylinder is extremely complex, involving many deformation parameters. In particular, the deformation shape of the V-shaped sidewall of the V-shaped sealing groove is very irregular. In order to quantify it, after comprehensive consideration, the protrusion of the standard steel ball is adopted as an indicator, which can effectively reflect a comprehensive variable.

[0045] In the technical solution of this application embodiment, the deformation of the sealing structure is simulated by multi-material staged extrusion, which avoids the need to conduct tests in a high temperature and high pressure environment, simplifies the simulation conditions, and demonstrates high economic efficiency; it avoids simulating according to several material replacement cycles (each cycle is 18 months), saving time costs; by using the progressive relationship of strength and hardness of different materials, plus the loading of different clamping forces in batches, the deformation in actual engineering is reproduced more accurately.

[0046] Furthermore, after the V-groove of the cylinder deforms, its cross-sectional shape becomes exceptionally complex, making it difficult to accurately describe using multiple variables. Even when simplified to a certain geometric relationship, it remains challenging to measure individual variables. For these reasons, this application employs a comprehensive calibration method based on the steel ball protrusion amount. This method allows for comprehensive calibration of the deformation and facilitates measurement. This application utilizes an indirect method to accurately measure the protrusion height of the standard steel ball, reducing the operational difficulty on-site and minimizing the labor intensity for workers.

[0047] The technical solution of this application has been applied to the simulation test of the main seal of the reactor pressure vessel. The test shows that the test method is suitable for the research and testing of the primary loop seal of VVER nuclear power plants, and can accurately, economically and quickly predict the deformation trend of the V-groove and top cover sealing plane of the reactor pressure vessel cylinder, as well as the sealing performance under extreme deformation. Moreover, the measurement method should be easy to operate. This application solves the problem of simulating and measuring the plastic deformation of the main sealing system (V-groove and sealing plane) of the reactor pressure vessel of a VVER nuclear power plant, providing test conditions for the study of the sealing safety of the reactor pressure vessel. At the same time, this method can also be applied to situations with similar sealing studies.

[0048] In at least one embodiment of this application, step S21 is a specific manifestation of step S2.

[0049] Step S21: Place a standard steel ball with a diameter of 5mm in the V-groove of the cylinder, and measure the amount of the standard steel ball protruding from the plane of the V-groove. The measurement result is the deformation of the V-groove of the cylinder and the sealing plane of the top cover.

[0050] Specifically, by placing a 5mm diameter ball into the V-shaped sealing groove of the test cylinder, the following method was adopted: Figure 3 The method described in the text measures the protrusion of the steel ball, and the result is the deformation of the V-groove of the cylinder and the sealing plane of the top cover.

[0051] It should be noted that the protrusion amount can also be called the protrusion value or protrusion height.

[0052] In at least one embodiment of this application, steps S211 and S212 are specific manifestations of step S21.

[0053] Step S211: Place the support block on the flat surface and place the standard steel ball into the through hole of the support block.

[0054] Step S212: Place a depth micrometer on the support block and measure the distance from the top of the standard steel ball to the upper surface of the support block. Finally, calculate the protrusion of the standard steel ball from the plane containing the V-groove. Protrusion = Support block thickness - Distance from the top of the standard steel ball to the upper surface of the support block.

[0055] A 5mm standard steel ball is placed into the V-groove of the cylinder. Due to the plastic deformation of the V-groove, the height of the standard steel ball in the V-groove is lower than before extrusion. Figure 4 As shown. Since the highest point of the standard steel ball is difficult to find, a support block (standard gauge block) is designed with a through hole of 7mm diameter. When it is necessary to measure the standard steel ball relative to the plane of the V-groove, the support block is placed on the plane, and the standard steel ball is placed in the through hole of the support block. Finally, a depth micrometer is placed on the support block, and the distance from the top of the standard steel ball to the upper surface of the support block can be easily measured. Finally, the protrusion of the standard steel ball from the plane of the V-groove can be calculated: Protrusion = Support block thickness - Distance from the top of the standard steel ball to the upper surface of the support block.

[0056] In at least one embodiment of this application, steps S11 to S13 are specific manifestations of step S1.

[0057] Step S11: The deformation is simulated sequentially using N6 pure nickel ring, stainless steel wire, and alloy steel wire. After each simulation, the helium leakage rate is tested first, and then a water pressure test is conducted at the maximum deformation value of the V-groove of the cylinder.

[0058] Step S12: If the water pressure test passes, the maximum value of the set cylinder V-shaped groove deformation is considered to be the maximum critical defect.

[0059] Step S13: If the hydrostatic test fails, reduce the maximum value of the V-shaped groove deformation of the cylinder and repeat the helium leakage rate test and hydrostatic test until the hydrostatic test passes, and find the maximum critical defect of the hydrostatic test.

[0060] Specifically, the test was conducted with the sealing structure using a nickel wire diameter of 5.00 mm, employing N6 pure nickel rings, stainless steel wire, and then alloy steel wire in that order. Figure 5 Under the tooling shown, the deformation of the sealing structure was simulated. After each simulation, the leakage rate of helium was tested first, followed by a water pressure test. Finally, the deformation of the V-shaped sealing groove of the cylinder and the sealing plane of the top cover was measured, and the corresponding test results were recorded.

[0061] It should be noted that the maximum critical defect can also be called the critical value of the hydrostatic test. The maximum deformation of the V-groove of the cylinder can also be called the maximum deviation of the sealing groove size or the theoretical maximum critical parameter.

[0062] In at least one embodiment of this application, the helium leakage rate test in step S1 is performed using a vacuum method. At the maximum load, under a pressure difference of 0.1 MPa and at room temperature, the helium leakage rate is recorded.

[0063] It should be noted that helium leakage rate testing can also be called helium detection testing. The helium leakage test system used for helium leakage rate testing consists of the following components: Figure 6 As shown.

[0064] In at least one embodiment of this application, the pressure of the water pressure test in step S1 is 30 MPa abs, the temperature is room temperature, and the pressure holding time is not less than 30 min.

[0065] In at least one embodiment of this application, the water pressure test in step S1 is to measure the pressure in the test chamber using a pressure gauge, with the range of the pressure gauge controlled at 1.5 to 2 times the test pressure.

[0066] For example, the water pressure testing system used in the water pressure test is as follows: Figure 7 As shown.

[0067] In at least one embodiment of this application, the test method for the main seal of the reactor pressure vessel of the nuclear power plant VVER unit further includes step S3.

[0068] Step S3: Supplementary test. Based on the results of the simulation test of the deformation of the sealing structure, select the limit dimensions of the V-groove of the cylinder and the sealing plane of the top cover, and use these as the object to conduct a sealing performance test.

[0069] In at least one embodiment of this application, the sealing performance test in step S3 includes a helium leakage rate test. The helium leakage rate test is conducted under the conditions of maximum load, at a pressure difference of 0.1 MPa, and at 350°C, recording the helium leakage rate.

[0070] In at least one embodiment of this application, the sealing performance test in step S3 includes a hydrostatic test, wherein the hydrostatic test conditions are a test pressure of 17.6 MPa abs, a test temperature of 350°C, and a pressure holding time of not less than 30 min.

[0071] It should be noted that the combination of the technical features in the embodiments of this application is not limited to the combination methods described in the embodiments of this application or the combination methods described in specific embodiments. All technical features described in this application can be freely combined or combined in any way, unless they contradict each other.

[0072] As indicated in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the term "comprising" only indicates that it includes the explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0073] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications or equivalent substitutions made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for testing the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant, characterized in that, include: Step S1: Multi-material staged extrusion simulation of the deformation of the sealing structure, and after each simulation, helium leakage rate test is performed first, and then hydrostatic test is performed at the maximum value of the V-groove deformation of the cylinder to obtain the maximum critical defect; the sealing structure consists of a pressure vessel, a pressure vessel top cover and a pure nickel sealing ring; Step S2: Use the steel ball protrusion to comprehensively calibrate the deformation of the cylinder V-groove and the sealing plane of the top cover.

2. The method for testing the main seal of the reactor pressure vessel of a nuclear power plant VVER unit according to claim 1, characterized in that, Step S2 includes: Step S21: Place a standard steel ball with a diameter of 5mm in the V-groove of the cylinder, and measure the amount of the standard steel ball protruding from the plane of the V-groove. The measurement result is the deformation of the V-groove of the cylinder and the sealing plane of the top cover.

3. The method for testing the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant according to claim 2, characterized in that, Step S21 includes: Step S211: Place the support block on the flat surface and place the standard steel ball into the through hole of the support block; Step S212: Place the depth micrometer on the support block and measure the distance between the top of the standard steel ball and the upper surface of the support block. Finally, calculate the amount of protrusion of the standard steel ball from the plane of the V-groove. Protrusion = thickness of the support block - distance between the top of the standard steel ball and the upper surface of the support block.

4. The method for testing the main seal of the reactor pressure vessel of a nuclear power plant VVER unit according to claim 1, characterized in that, Step S1 includes: Step S11: The deformation is simulated by N6 pure nickel ring, stainless steel wire and alloy steel wire in sequence. After each simulation, the leakage rate of helium is tested first, and then the water pressure test is carried out under the maximum deformation of the V-groove of the cylinder. Step S12: If the water pressure test passes, the maximum value of the set cylinder V-groove deformation is considered to be the maximum critical defect. Step S13: If the hydrostatic test fails, reduce the maximum value of the V-shaped groove deformation of the cylinder and repeat the helium leakage rate test and hydrostatic test until the hydrostatic test passes, and find the maximum critical defect of the hydrostatic test.

5. The method for testing the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant according to claim 1, characterized in that, In step S1, the helium leakage rate test was conducted using the vacuum method. At the maximum load, under a pressure difference of 0.1 MPa and at room temperature, the helium leakage rate was recorded.

6. The method for testing the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant according to claim 1, characterized in that, In step S1, the water pressure test is performed at a pressure of 30 MPa abs, at room temperature, and for a holding time of no less than 30 minutes.

7. The method for testing the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant according to claim 1, characterized in that, In step S1, the water pressure test involves using a pressure gauge to measure the pressure inside the test chamber, with the gauge range controlled at 1.5 to 2 times the test pressure.

8. A method for testing the main seal of the reactor pressure vessel of a nuclear power plant VVER unit according to any one of claims 1 to 7, characterized in that, Also includes: Step S3: Supplementary test. Based on the results of the simulation test of the deformation of the sealing structure, select the limit dimensions of the V-groove of the cylinder and the sealing plane of the top cover, and use these as the object to conduct a sealing performance test.

9. The method for testing the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant according to claim 1, characterized in that, The sealing performance test in step S3 includes a helium leakage rate test. The helium leakage rate test is conducted under the conditions of maximum load, at a pressure difference of 0.1 MPa, and at 350°C, and the helium leakage rate is recorded.

10. The method for testing the main seal of the reactor pressure vessel of a VVER unit in a nuclear power plant according to claim 1, characterized in that, The sealing performance test in step S3 includes a hydrostatic test. The conditions for the hydrostatic test are a test pressure of 17.6 MPaabs, a test temperature of 350℃, and a pressure holding time of not less than 30 minutes.

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