Commissioning Method for Accident Discharge Pipeline of Blowdown System of Steam Generator in Pressurized Water Reactor Nuclear Power Plant

Abstract

The present invention belongs to the technical field of nuclear power plant safety, and particularly relates to a commissioning method for the accident discharge pipeline of the steam generator blowdown system in a pressurized water reactor nuclear power plant. There are several accident discharge pipelines (2) in the steam generator blowdown system, and each accident discharge pipeline (2) corresponds to one steam generator (1). It is led out from the steam generator (1) and directly connected to the in-containment refueling water storage tank (4). A drain isolation valve (3) is provided on the accident discharge pipeline. The commissioning method includes the following steps: Step S1, determining the test purpose; Step S2, determining the initial test conditions; Step S3, determining the acceptance criteria; Step S4, determining the test content. The present invention fills the domestic blank in the commissioning design method of the accident discharge pipeline of the steam generator blowdown system, can verify the correctness of the performance of the accident discharge pipeline of the steam generator blowdown system and the compliance of the design, and lays a foundation for the smooth progress of subsequent on-site commissioning.

Description

Technical Field

[0001] The present invention belongs to the technical field of nuclear power plant safety, and particularly relates to a commissioning method for an accident discharge pipeline of a steam generator blowdown system in a pressurized water reactor nuclear power plant. Background Art

[0002] After the Fukushima nuclear accident in Japan, according to the adjustment of China's nuclear energy policy and the development of international trends, newly built nuclear power plants in China will adopt advanced pressurized water reactor nuclear power technologies with higher safety and stronger accident resistance. Advanced pressurized water reactor nuclear power plants first improve the overall safety of nuclear power plants from a design perspective. Most of their design concepts are based on the design, manufacturing, construction, and operation experience of second-generation improved pressurized water reactor nuclear power plants, and new design concepts and items with new design characteristics are introduced.

[0003] In the design of a typical steam generator blowdown system of a second-generation improved pressurized water reactor nuclear power plant, in the case of a steam generator tube rupture accident (SGTR), in order to limit the increase in the water level of the damaged steam generator, the blowdown system manually resumes operation for maximum flow blowdown, and the blowdown water is cooled and then discharged into the nuclear island liquid waste discharge system to prevent the damaged steam generator from overflowing. However, it should be noted that the pipelines and equipment downstream of the containment isolation valve outside the containment of the steam generator blowdown system and the liquid waste discharge system are all non-safety-class.

[0004] The existing steam generator blowdown system of a pressurized water reactor nuclear power plant adds an accident discharge pipeline to the blowdown pipeline inside the containment, and discharges the leaked liquid in the damaged steam generator into the containment sump, realizing the adjustment of the water level and pressure of the damaged steam generator in the SGTR accident, thus meeting the requirement of undertaking safety functions.

[0005] Due to the design change of the steam generator blowdown system, tests on the accident discharge pipeline need to be carried out during the commissioning stage of the nuclear power plant, and the accident discharge pipeline is verified whether it meets the accident analysis requirements by testing the functions of the accident discharge pipeline.

[0006] Since the medium state in the pipeline is a vapor-liquid two-phase when using the accident discharge pipeline, the flow rate of the vapor-liquid two-phase cannot be accurately measured under hot conditions, and the discharge capacity of the accident discharge pipeline cannot be verified. Through the retrieval of domestic and foreign literatures, no publicly published literature related to the commissioning of the accident discharge pipeline has been found, nor are there relevant design documents or literatures explaining how to commission and verify this function. Summary of the Invention

[0007] After the installation of the accident discharge pipeline of the steam generator blowdown system in a pressurized water reactor nuclear power plant is completed, it enters the commissioning stage, and its performance is verified to meet the design requirements through system commissioning. Since the accident discharge pipeline is a new design, there is currently no method for commissioning the accident discharge pipeline, resulting in an increase in the commissioning difficulty and workload. The purpose of the present invention is to provide a commissioning method for the accident discharge pipeline of the steam generator blowdown system to ensure the smooth and orderly development of the commissioning work of the accident discharge pipeline of the steam generator blowdown system, formulate the content of the commissioning procedure document, and verify the performance of the accident discharge pipeline. This method is based on the design characteristics of the accident discharge pipeline, and by analyzing the functions and configurations of the accident discharge pipeline, commissioning test items for the accident discharge pipeline are designed, including test purposes, acceptance criteria, initial conditions, test contents, etc.

[0008] To achieve the above object, the technical solution adopted by the present invention is a commissioning method for the accident discharge pipeline of the steam generator blowdown system in a pressurized water reactor nuclear power plant. There are several accident discharge pipelines in the steam generator blowdown system, and each accident discharge pipeline corresponds to one steam generator, leading out from the steam generator and directly connected to the in-containment refueling water storage tank. A drain isolation valve is provided on the accident discharge pipeline. The commissioning method includes the following steps:

[0009] Step S1, determine the test purpose

[0010] Analyze the requirements for the functions of the accident discharge pipeline according to the functions and design documents of the accident discharge pipeline, and determine the test purpose.

[0011] Step S2, determine the test initial conditions

[0012] According to the functions of the accident discharge pipeline, determine that the test is carried out in the hot state performance test stage, and the parameters of the steam generator need to be set.

[0013] Step S3, determine the acceptance criteria

[0014] Based on the sorting and analysis of the functions of the accident discharge pipeline, convert the acceptance method of the functions of the accident discharge pipeline into a test method for on-site commissioning personnel to operate, so as to formulate the acceptance criteria under the hot state performance test conditions.

[0015] Step S4, determine the test content

[0016] It includes calculating the volume of the discharged water through the value of the decrease in the secondary side liquid level of the steam generator within a certain period of time during the hot state performance test stage, and then calculating the discharge mass flow rate; the certain period of time refers to the time from the start to the end of the discharge.

[0017] It also includes determining the test process, test error analysis, and test result analysis based on the function of the accident discharge pipeline, test purpose, parameter settings of the steam generator during the designed test process, and acceptance criteria.

[0018] Further, in the step S1, the purpose of the test is to verify whether the discharge flow rate of the accident discharge pipeline meets the requirements.

[0019] Further, before the step S2, it also includes selecting the discharge starting point and discharge ending point of the test. The discharge starting point is selected at the +0.6 m position of the water level of the steam generator, and the discharge ending point is selected at the +0 m position of the water level of the steam generator.

[0020] Further, in the step S2, select the accident discharge pipeline with the longest length and the greatest resistance for the test. The power supply of the drain isolation valve on the selected accident discharge pipeline has been turned on. Before the test, the secondary side pressure of the steam generator connected to the selected accident discharge pipeline reaches 4.0 MPa.a. Personnel in the plant have been evacuated; adjust the water level of the steam generator to the discharge starting point and the pressure to 4.0 MPa.a.

[0021] Further, during the test process of the step S4, record the full - open time of the drain isolation valve as the start - discharge time. When the water level of the steam generator drops to the position of the discharge ending point, close the drain isolation valve to end the discharge. The time when the drain isolation valve starts to close is the end - discharge time, and record the discharge time of the test.

[0022] Further, after the test process, perform discharge flow calculation. Calculate the average value of the liquid level of the steam generator measured by the measuring instrument at the discharge starting point; calculate the average value of the liquid level measured by the measuring instrument at the discharge ending point, calculate the volume of the discharged water, and then calculate the discharge flow rate based on the discharge time.

[0023] Further, after obtaining the discharge flow rate, analyze the errors of the liquid level measurement channel, pressure measurement channel, and equipment manufacturing error of the steam generator during the test, and calculate the comprehensive error of the test.

[0024] Further, in the step S3, determine the acceptance criteria as the discharge capacity of the accident discharge pipeline being the discharge flow rate ≥ 4.74 kg / s, and at the same time the secondary side of the steam generator is in a saturated state and the pressure is 4.0 MPa.a; the discharge flow rate meets the acceptance criteria, which indicates that the design requirements of the accident discharge pipeline of the steam generator blowdown system are met.

[0025] The beneficial effects of the present invention are as follows:

[0026] In step S1 of the present invention, by analyzing the functions of the accident discharge pipeline, the stages that need to be debugged are determined. The purpose is to determine the stages that need to be debugged according to the main functions of the accident discharge pipeline, so as to provide reference and basis for the performance analysis of the accident discharge pipeline. In the past, there was no debugging design method for the accident discharge pipeline of the steam generator blowdown system in domestic pressurized water reactor nuclear power plants, and the present invention fills this gap.

[0027] In step S2 of the present invention, debugging tests are carried out during the hot state performance test stage, ensuring that the functions are verified under the actual use conditions of the accident discharge pipeline of the steam generator blowdown system, so as to reasonably formulate a method for debugging the functions of the accident discharge pipeline of the steam generator blowdown system.

[0028] In step S3 of the present invention, by designing acceptance criteria, the discharge capacity of the accident discharge pipeline of the steam generator blowdown system is equivalently transformed into test parameters that are easy for on-site debugging personnel to use. This can not only ensure that the functions of the accident discharge pipeline of the steam generator blowdown system meet the design requirements, but also make it easier for on-site debugging personnel to operate, laying a foundation for the smooth progress of subsequent on-site debugging.

[0029] Step S4 of the present invention can verify the correctness of the performance of the accident discharge pipeline of the steam generator blowdown system and the compliance of the design. Description of the Drawings

[0030] Figure 1 is a flowchart of the debugging method for the accident discharge pipeline of the steam generator blowdown system of the pressurized water reactor nuclear power plant described in the specific embodiment of the present invention;

[0031] Figure 2 is a schematic diagram of the accident discharge pipeline of the steam generator blowdown system of the pressurized water reactor nuclear power plant described in the specific embodiment of the present invention;

[0032] In the figure: 1 - steam generator, 2 - accident discharge pipeline, 3 - drain isolation valve, 4 - in-containment refueling water storage tank, 5 - containment, 6 - out-of-containment isolation valve, 7 - check valve (for preventing medium backflow), 8 - manual isolation valve. Specific Embodiment

[0033] The present invention will be further described below with reference to the drawings and embodiments.

[0034] The debugging method for the accident discharge pipeline of the steam generator blowdown system of the pressurized water reactor nuclear power plant provided by the present invention (as Figure 1 shown), the steam generator blowdown system (as Figure 2There are several accident discharge pipelines 2 (as shown), and each accident discharge pipeline 2 corresponds to a steam generator 1. It is led out from the steam generator 1 and directly connected to the in-containment refueling water storage tank 4. A drain isolation valve 3 is provided on the accident discharge pipeline. The commissioning method includes the following steps:

[0035] Step S1, determine the test purpose (the "test" refers to the commissioning test, the same below)

[0036] Analyze the requirements for the functions of the accident discharge pipeline 2 based on the main functions of the accident discharge pipeline 2 and relevant design documents, and determine the test purpose;

[0037] Step S2, determine the initial conditions of the (commissioning) test

[0038] According to the functions of the accident discharge pipeline 2, determine that the test is carried out in the hot functional test stage, and the main parameters of the steam generator 1 need to be set to ensure the smooth progress of the test; where "hot state" means heating up and increasing pressure without nuclear fuel loading to simulate the actual operating conditions of a nuclear power plant.

[0039] Step S3, determine the acceptance criteria

[0040] Based on the sorting out and analysis of the functions of the accident discharge pipeline 2, equivalently transform the acceptance method of the functions of the accident discharge pipeline 2 into a test method that is easy for on-site commissioning personnel to operate, so as to formulate the acceptance criteria under the hot functional test conditions;

[0041] Step S4, determine the test content

[0042] Since the inside of the steam generator 1 is saturated water or slightly subcooled water during the hot functional test, and the in-containment refueling water storage tank 4 is an open pool with atmospheric pressure on the liquid surface, two-phase flow will occur in the accident discharge pipeline 2 during the hot functional test. Therefore, it is impossible to directly measure the flow rate using an on-line flow measurement device;

[0043] Step S4 includes calculating the volume of discharged water through the decrease value of the secondary side liquid level of the steam generator 1 within a period of time during the hot functional test stage, and then calculating the discharge mass flow rate; a period of time refers to the time from the start to the end of the discharge;

[0044] It also includes determining the commissioning test process, test error analysis, test result analysis, etc. according to the functions of the accident discharge pipeline 2, test purpose, main parameter settings of the steam generator 1 during the design test process, acceptance criteria, etc.

[0045] The main function of the accident discharge pipeline of the steam generator blowdown system in a pressurized water reactor nuclear power plant is to drain the leaked liquid in the damaged steam generator 1 to the in-containment refueling water storage tank 4 by opening the motorized drain isolation valve 3 on the accident discharge pipeline 2 of the steam generator blowdown system, reducing the pressure of the damaged steam generator 1, and at the same time restricting the water level of the damaged steam generator 1 to prevent the damaged steam generator 1 from overflowing; in the later stage of the SGTR accident, the operator can monitor the state of the damaged steam generator 1 according to the procedures and adjust the pressure and water level of the damaged steam generator 1 by manually opening and closing a drain isolation valve 3 of the accident discharge pipeline in the main control room to ensure that the damaged steam generator 1 does not overflow. Therefore, in step S1, the purpose of the test is to verify whether the discharge flow rate of the accident discharge pipeline 2 meets the requirements.

[0046] Before step S2, it also includes selecting the discharge starting point and the discharge ending point of the test. The discharge starting point is selected at the position of +0.6 m of the water level of the steam generator 1, and the discharge ending point is selected at the position of +0 m of the water level of the steam generator 1 (i.e., the discharge ends when the water level reaches +0 m). If the discharge time of the accident discharge pipeline test is too short, the decrease in the steam generator liquid level is not obvious, which may lead to an increase in measurement error. If the discharge time of the accident discharge pipeline test is too long, it may cause the in-containment refueling water storage tank to heat up too much, and it is possible that the discharged steam-water mixture cannot be completely absorbed by the cold water in the pool and directly enters the environment, increasing the temperature inside the containment. Therefore, it is necessary to determine a reasonable discharge starting point and ending point to make the test results credible and not affect the environmental conditions inside the containment. After a conservative decision, the initial liquid level is selected as +0.6 m, and the discharge ends at +0 m.

[0047] In step S2, select the accident discharge pipeline 2 with the longest length and the greatest resistance for the test. The power supply of the drain isolation valve 3 (the drain isolation valve 3 is a motorized drain isolation valve) on the selected accident discharge pipeline 2 has been connected. Before the test, the secondary side pressure of the steam generator 1 connected to the selected accident discharge pipeline 2 reaches 4.0 MPa.a. Personnel in the plant have been evacuated to prevent unauthorized personnel from entering the test area; adjust the water level of the steam generator 1 to be at the discharge starting point (about +0.6 m) and the pressure to be at about 4.0 MPa.a.

[0048] During the test in step S4 after step S2, record the full-open time of the drain isolation valve 3 as the start discharge time. When the water level of the steam generator 1 drops to the position of the discharge ending point (about +0 m), close the drain isolation valve 3 to end the discharge. The time when the drain isolation valve 3 starts to close is the end discharge time, and record the discharge time of the test.

[0049] After the test process, the discharge flow rate is calculated. The average liquid level of steam generator 1 measured by the measuring instrument at the discharge starting point (i.e., the initial liquid level of the test) is calculated; the average liquid level measured by the measuring instrument at the discharge end point (i.e., the ending liquid level of the test) is calculated, the discharge water volume is calculated, and then the discharge flow rate is obtained based on the discharge time.

[0050] After obtaining the discharge flow rate, analyze the errors of the liquid level measurement channel, pressure measurement channel, and manufacturing errors of the steam generator equipment in the test, and calculate the comprehensive error of the test.

[0051] In step S3, in order to make the test as close as possible to the actual accident condition, it is determined to conduct an accident discharge pipeline test during the hot state performance test. According to the analysis of the SGTR accident process, the acceptance criterion is that the discharge capacity of accident discharge pipeline 2 is the discharge flow rate ≥ 4.74 kg / s, and at the same time, the secondary side of steam generator 1 corresponding to this mass flow rate is in a saturated state and the pressure is 4.0 MPa.a; the discharge flow rate meets the acceptance criterion, which indicates that the design requirements of accident discharge pipeline 2 of the steam generator blowdown system are met; the acceptance criterion provides a judgment standard for the test results for on-site commissioning personnel.

[0052] Finally, an example is given to illustrate the test process part (including error analysis and result analysis) of the method for commissioning the accident discharge pipeline of the steam generator blowdown system of a pressurized water reactor nuclear power plant provided by the present invention.

[0053] The initial liquid level is selected as +0.6 m, and the discharge ends at +0 m. The test discharge time is recorded as 1199 s, and the liquid level change during the test is 582.5 mm. The pressure during the discharge test is 4.04 MPa.a, and the calculated discharge water volume is the discharge volume of 8.3 m 3 , and then the discharge flow rate of 5.52 kg / s is obtained based on the discharge time of 1199 s.

[0054] The total error of the liquid level measurement channel is 0.847%, the total error of the pressure measurement channel is 0.804%, and the volume deviation caused by the manufacturing of the steam generator related to the accident discharge pipeline test is 0.14%. The calculated comprehensive error of the test is 1.176%.

[0055] The acceptance criterion value q a = 4.74 / s. After considering the test error of 1.176%, the flow rate value obtained by converting the positive deviation is:

[0056] q t ≥ (1 + 1.176%) * 4.74 kg / s = 4.796 kg / s

[0057] The mass of the discharged fluid in the test value of 5.52 kg / s is converted into the discharge flow rate at a pressure of 4.0 MPa.a as 5.45 kg / s.

[0058] 5.45 kg / s > 4.796 kg / s, so the test results meet the requirements of the acceptance criteria.

[0059] Considering the comprehensive error of the test and taking the negative deviation, the test value of 5.386 kg / s is obtained for 5.45 kg / s. Since 5.386 kg / s > 4.74 kg / s, the test results meet the requirements of the acceptance criteria.

[0060] The device described in the present invention is not limited to the embodiments described in the specific embodiments. Other embodiments obtained by those skilled in the art according to the technical solution of the present invention also fall within the scope of the technical innovation of the present invention.

Claims

1. Commissioning method for accident discharge pipeline of steam generator blowdown system in pressurized water reactor nuclear power plant. The accident discharge pipelines (2) of the steam generator blowdown system are several, and each accident discharge pipeline (2) corresponds to one steam generator (1), leading out from the steam generator (1) and directly connected to the in-containment refueling water storage tank (4). A drain isolation valve (3) is provided on the accident discharge pipeline. The commissioning method includes the following steps: Step S1, determine the test purpose. Analyze the requirements for the functions of the accident discharge pipeline (2) according to the functions and design documents of the accident discharge pipeline (2) to determine the test purpose. Step S2, determine the initial test conditions. According to the functions of the accident discharge pipeline (2), determine that the test is carried out in the hot functional test stage and the parameters of the steam generator (1) need to be set. Step S3, determine the acceptance criteria. Based on the sorting and analysis of the functions of the accident discharge pipeline (2), convert the acceptance method of the functions of the accident discharge pipeline (2) into a test method for on-site commissioning personnel to operate, so as to formulate the acceptance criteria under the hot functional test conditions. Step S4, determine the test content. It includes calculating the volume of discharged water by the drop value of the secondary side liquid level of the steam generator (1) within a certain period of time during the hot functional test stage, and then calculating the discharge mass flow rate. The certain period of time refers to the time from the start to the end of the discharge. It also includes determining the test process, test error analysis, and test result analysis according to the functions of the accident discharge pipeline (2), test purpose, parameter settings of the steam generator (1) during the design test process, and acceptance criteria. In step S1, the purpose of the test is to verify whether the discharge flow rate of the accident discharge pipeline (2) meets the requirements. Before step S2, it also includes selecting the discharge starting point and discharge ending point of the test. The discharge starting point is selected at the +0.6 m position of the water level of the steam generator (1), and the discharge ending point is selected at the +0 m position of the water level of the steam generator (1). In step S2, select the accident discharge pipeline (2) with the longest length and the greatest resistance for the test. The power supply of the drain isolation valve (3) on the selected accident discharge pipeline (2) has been connected. Before the test, the secondary side pressure of the steam generator (1) connected to the selected accident discharge pipeline (2) reaches 4.0 MPa.a, and the personnel in the plant have been evacuated. Adjust the water level of the steam generator (1) to the discharge starting point and the pressure to 4.0 MPa.a. In step S3, determine the acceptance criteria as the discharge capacity of the accident discharge pipeline (2) is discharge flow rate ≥ 4.74 kg / s, and at the same time the secondary side of the steam generator (1) is in a saturated state and the pressure is 4.0 MPa.a. The discharge flow rate meets the acceptance criteria, which indicates that the design requirements of the accident discharge pipeline (2) of the steam generator blowdown system are met. After the said test process, the discharge flow rate is calculated. The average value of the liquid level of the steam generator (1) measured by the measuring instrument at the discharge starting point is calculated; the average value of the liquid level measured by the measuring instrument at the discharge end point is calculated, the discharged water volume is calculated, and then the discharge flow rate is obtained according to the discharge time. After obtaining the discharge flow rate, the errors of the liquid level measurement channel, the pressure measurement channel, and the manufacturing error of the steam generator equipment in the test are analyzed, and the comprehensive error of the test is calculated. Considering the comprehensive error of the test, the acceptance criterion value of 4.74 kg / s is converted with a positive deviation to obtain the flow rate value, and the test value of the discharge flow rate is converted into the discharge flow rate at a pressure of 4.0 MPa.a. It is compared whether the test value of the converted discharge flow rate is greater than the flow rate value obtained by the positive deviation conversion. Moreover, the test value with a negative deviation is obtained by considering the comprehensive error of the test for the test value of the converted discharge flow rate, and it is compared whether the test value with a negative deviation is greater than the acceptance criterion value of 4.74 kg / s, so as to determine whether the test result meets the requirements of the acceptance criterion.

2. The commissioning method for the accident discharge pipeline of the steam generator blowdown system of a pressurized water reactor nuclear power plant as described in claim 1, characterized in that: during the test process of step S4, the full-open time of the drain isolation valve (3) is recorded as the start discharge time. When the water level of the steam generator (1) drops to the position of the discharge end point, the drain isolation valve (3) is closed to end the discharge, and the start closing time of the drain isolation valve (3) is the end discharge time, and the discharge time of the test is recorded.

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