Hydraulic pressure test method for strength of primary loop of nuclear power unit

Abstract

The invention relates to the technical field of nuclear power, in particular to a nuclear power unit primary circuit strength water pressure test method. The nuclear power unit primary circuit strength hydraulic pressure test method comprises the following steps: preparing equipment participating in the test; completing system online according to a hydrostatic test boundary, and performing a hydrostatic test in a primary loop cold state; reducing the pressure and the liquid level of the primary loop, establishing a nitrogen cushion in a pressure stabilizer, and starting a main pump to heat the primary loop to a hydrostatic test temperature after exhausting; the frequency converter adjusts the charging pump to gradually increase the primary loop pressure to each test platform for leak detection, then the frequency converter is used to gradually increase the outlet flow of the strength hydrostatic test pump, the primary loop pressure is increased to the pressure of the strength hydrostatic test platform, and then the primary loop pressure is reduced to the leak detection platform for leak detection; carrying out secondary loop strength hydraulic pressure test in cooperation with primary loop pressure reduction; recovering the system state after the hydrostatic test and preparing to heat the reactor. According to the invention, the accuracy and reliability of the test are effectively improved, the potential damage risk to the component is reduced, and the test period is shortened.

Description

Technical Field

[0001] The present invention relates to the field of nuclear power technology, and particularly to a method for strength hydrostatic test of the primary loop of a nuclear power unit. Background Art

[0002] In accordance with the requirements of nuclear safety regulations, in order to test the strength and integrity of pipelines and equipment, the operating unit of a nuclear power plant needs to regularly conduct pressure tests during the operation of the unit. According to different inspection purposes, the pressure tests are divided into strength hydrostatic tests and leak tightness tests.

[0003] As a highly complex and extremely safety - demanding energy system, the pressure - bearing components of a nuclear power plant (such as pressure vessels, primary coolant pumps, steam generators, pressurizers, primary pipes, valves, etc.) need to withstand extremely high pressures and temperatures under normal operation and accident conditions. Hydrostatic test, as an important means to test the strength and leak tightness of these components, is crucial for ensuring the safety of nuclear power plants. However, the traditional primary loop hydrostatic test method has the following defects:

[0004] (1) Long test duration: The test requires the unit to be shut down, which affects power generation efficiency and economy. The equipment operates at a pressure higher than the design pressure for a long time, with a relatively high potential damage risk to the primary loop pressure - bearing components. Moreover, with the long - term heating of the reactor residual heat, there is a high risk of false operation of the reactor and the dedicated safety system protection due to the over - limit temperature of the primary coolant.

[0005] (2) High over - pressure risk: It is difficult to control the pressure platform using the recirculation valve of the strength hydrostatic test pump, and there is a risk that the equipment exceeds the leak detection pressure platform, which may cause a primary loop over - pressure break, with relatively high nuclear safety risks and industrial safety risks.

[0006] (3) High operation difficulty: Using the recirculation valve of the strength hydrostatic test pump to control the pressure rise rate requires high skills and fine operation levels of on - site operators. It is difficult to control the pressure rise rate, and the uncontrollable pressure rise and fall process of the primary loop will bring greater stress to the equipment. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: to provide a method for strength hydrostatic test of the primary loop of a nuclear power unit, which effectively improves the accuracy and reliability of the test, reduces the potential damage risk to components, shortens the test cycle, improves work efficiency, and provides a strong guarantee for the safe operation of nuclear power plants by optimizing the test process and precisely controlling the test conditions and process.

[0008] The present invention provides a method for strength hydrostatic test of the primary loop of a nuclear power unit, including the following steps:

[0009] Step 1: Prepare the equipment participating in the test;

[0010] Step 2: Complete the system online according to the hydraulic test boundary and conduct a cold hydraulic test on the primary circuit;

[0011] Step 3: Reduce the pressure and liquid level of the primary circuit, and build a nitrogen cushion in the regulator. After exhausting, start the main pump to heat the primary circuit to the water pressure test temperature;

[0012] Step 4: The inverter adjusts the charging pump to gradually increase the primary circuit pressure to each test platform for leak detection. Then, the inverter is used to gradually increase the outlet flow of the strength water pressure test pump to raise the primary circuit pressure to the strength water pressure test platform pressure, and then reduce the pressure to the leak detection platform for leak detection.

[0013] Step 5: Reduce the pressure of the primary circuit and conduct a water pressure test on the secondary circuit;

[0014] Step 6: After the hydrostatic test, restore the system to prepare for heating the reactor.

[0015] In a specific embodiment of the present invention, step 1 specifically includes:

[0016] Step 1-1: Confirm that the equipment involved in the test is in good condition;

[0017] The equipment involved in the test includes primary circuit main equipment, charging pump, water pressure test pump, and discharge regulating valve;

[0018] Step 1-2: Connect the inverter cable of a charging pump to the strength water pressure test pump, and test run the strength water pressure test pump to ensure that the inverter is usable;

[0019] Step 1-3: Check and close all valves and channels within the primary circuit hydrostatic test boundary to ensure that pressure does not leak to other systems during the test.

[0020] In a specific embodiment of the present invention, step 2 specifically includes:

[0021] Step 2-1: Fill the primary circuit and exhaust it fully to ensure that the primary circuit is completely filled;

[0022] Step 2-2: Use the charging pump to inject coolant into the primary circuit, increase the primary circuit pressure to 3.2 MPa at a rate not exceeding 0.98 MPa / min, and perform a leak check.

[0023] In a specific embodiment of the present invention, step 3 specifically includes:

[0024] Step 3-1: After the cold test is completed, reduce the pressure and liquid level of the primary circuit, and fill the pressure regulator with nitrogen to ensure the suction pressure head for starting the main pump;

[0025] Step 3-2: Start the reactor primary coolant pump for a short time to conduct dynamic exhaust of the primary loop, ensuring that the non-condensable gases in the primary loop equipment and pipelines are fully discharged;

[0026] Step 3-3: Start the reactor primary coolant pump again to heat the primary loop to the hydrostatic test temperature, preventing cold embrittlement of the equipment.

[0027] In a specific embodiment of the present invention, the pressure of the primary loop drops to 1.5 - 1.8 Mpa; the hydrostatic test temperature is not lower than 115 °C.

[0028] In a specific embodiment of the present invention, the specific steps of Step 4 are as follows:

[0029] Step 4-1: Stop the reactor primary coolant pump and the residual heat removal system;

[0030] Step 4-2: Drain the nitrogen in the pressurizer, restore the hydrostatic test boundary according to the program requirements, and refill the primary loop main equipment and the connected pipelines;

[0031] Step 4-3: Use a temporary device to lock the pressurizer safety valve group to prevent the pressurizer safety valve from operating during the hydrostatic test;

[0032] Step 4-4: Adjust the charging pump to increase the pressure of the primary loop to each test pressure platform at a rate not exceeding 0.98 MPa / min and maintain it. During this period, control the pressure increase rate of the primary loop not to exceed the limit, and conduct leak detection at the same time;

[0033] During the hydrostatic test of the primary loop, control the feed water temperature of the steam generator and the main steam discharge amount of the secondary loop to ensure that the temperature of the primary loop coolant is within the range required for the hydrostatic test;

[0034] Step 4-5: Gradually increase the outlet flow of the intensity hydrostatic test pump using a temporary frequency converter to raise the pressure of the primary loop to the intensity hydrostatic test platform. During this period, control the pressure increase rate of the primary loop not to exceed the limit. After maintaining for 10 - 20 minutes, reduce the pressure to the leak detection platform for leak detection.

[0035] In a specific embodiment of the present invention, in Step 4-4, there are 4 test pressure platforms, and the pressures of each test platform are 3.2 MPa, 9.8 MPa, 15.7 MPa, and 17.6 MPa respectively.

[0036] In a specific embodiment of the present invention, in Step 4-5, the temporary frequency converter adjusts the frequency of the intensity hydrostatic test pump of the primary loop to continue increasing the pressure of the primary loop to the 22 MPa intensity hydrostatic test platform at a rate not exceeding 0.98 MPa / min.

[0037] In a specific embodiment of the present invention, the specific steps of Step 5 are as follows:

[0038] Step 5-1: By adjusting the letdown flow rate and the frequency of the hydrostatic test pump, reduce the primary loop pressure at a rate not exceeding 0.98 MPa / min to 12 MPa, then maintain this pressure and conduct the secondary loop strength hydrostatic test in coordination;

[0039] Step 5-2: After the secondary loop strength hydrostatic test is completed, continue to reduce the primary loop pressure to the range required by the technical regulations.

[0040] In a specific embodiment of the present invention, the said Step 6 specifically includes:

[0041] Step 6-1: The primary loop continues to depressurize to 1.5 - 1.8 MPa and establish a nitrogen cushion in the pressurizer;

[0042] Step 6-2: Resume the operation of the reactor auxiliary system and start the reactor primary coolant pump to heat the reactor to the hot state.

[0043] Compared with the prior art, the method for the primary loop strength hydrostatic test of the nuclear power unit of the present invention has the following

[0044] Advantages:

[0045] (1) The present invention uses a temporary device to externally connect a frequency converter to the strength hydrostatic test pump. The operator controls the output and flow rate of the strength hydrostatic test pump by adjusting the frequency converter, so as to realize the stable and controllable rise of the primary loop pressure during the strength hydrostatic test and maintain it at the pressure platform required by the test;

[0046] (2) The present invention uses a frequency converter to precisely control the test pressure during the pressure rise process, which can effectively avoid overpressure in the primary loop during the hydrostatic test operation, reduce the nuclear safety risk and operation risk;

[0047] (3) The present invention can effectively control the residual heat of the reactor during the test by controlling the feed water temperature of the steam generator and the main steam discharge amount of the secondary loop, avoid misoperation of the reactor and the dedicated safety system protection caused by the overlimit of the primary loop coolant temperature, and reduce the nuclear safety risk and operation risk;

[0048] (4) The present invention cancels the use of the hydrostatic test pump recirculation valve to control the pressure rise speed, can effectively control the pressure change rate of the primary loop equipment and pipelines during the test, shortens the operation time of the equipment in the high-pressure range, and reduces the potential damage risk to the components;

[0049] (5) The present invention uses a frequency converter to precisely control the test pressure during the pressure rise process, can significantly shorten the test duration, reduce the unit outage time, and increase the economic benefits of the generating unit;

[0050] (6) The present invention cancels the use of the recirculation valve of the hydrostatic test pump to control the pressure rising speed, significantly reducing the operation difficulty of personnel during the hydrostatic test, improving the work efficiency and saving manpower.

[0051] (7) The present invention controls the pressure precisely, actually reducing the test pressure and the industrial safety and radiation safety risks of the inspection personnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It shows a simplified diagram of the boundary of the primary circuit strength hydrostatic test of the reactor;

[0053] In the figure,

[0054] 1 - Reactor; 2 - Primary coolant pump; 3 - Steam generator; 4 - Pressurizer; 5 - Primary coolant pipe of the reactor; 6 - Medium-pressure safety injection pipe; 7 - Pressurizer emergency spray pipe; 8 - Emergency boron injection pipe; 9 - High-pressure safety injection pipe; 10 - Low-pressure safety injection pipe; 11 - Residual heat removal pipe; 12 - Volume and boron control system pipe; 13 - Primary circuit strength hydrostatic test pump. DETAILED DESCRIPTION OF THE INVENTION

[0055] In order to further understand the present invention, the implementation scheme of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the present invention.

[0056] The present invention uses a temporary device to externally connect a frequency converter to the primary circuit strength hydrostatic test pump, and controls the output and flow of the strength hydrostatic test pump by adjusting the frequency converter, so as to realize the stable and controllable rise of the primary circuit pressure during the strength hydrostatic test and maintain it at the pressure platform required by the test.

[0057] As Figure 1 shown, the primary coolant of the reactor 1 enters the reactor through the primary coolant pipe driven by the primary coolant pump 2. After the coolant absorbs the heat released by the fission reaction in the reactor, it flows out of the reactor, enters the steam generator 3 through the primary coolant pipe, is cooled by the secondary circuit medium in the steam generator, and then returns to the inlet of the main pump of each loop to form a closed cycle. A pressurizer 4 is arranged on the third and fourth loops to maintain the primary circuit pressure during the reactor power operation; a medium-pressure safety injection pipe 6, a high-pressure safety injection pipe 9, a low-pressure safety injection pipe 10, an emergency boron injection pipe 8, a residual heat removal pipe 11, and a pressurizer emergency spray pipe 7 are arranged on the primary coolant pipe of the reactor for ensuring the safe shutdown of the reactor in case of an accident; a volume and boron control system pipe 12 is also arranged on the primary coolant pipe 5 of the reactor for filling the primary circuit and compensating for the change in the coolant water inventory.

[0058] When conducting the primary circuit strength hydrostatic test, externally connect a frequency converter to the primary circuit strength hydrostatic test pump 13, and control the outlet flow of the strength hydrostatic test pump by adjusting the frequency of the frequency converter, so as to achieve a smooth rise in the primary circuit pressure and maintain it at the pressure platform required by the test.

[0059] An embodiment of the present invention discloses a method for the primary circuit strength hydrostatic test of a nuclear power unit, including the following steps:

[0060] Step 1: Prepare the equipment participating in the test;

[0061] Specifically,

[0062] Step 1-1: Confirm that the equipment participating in the test is in good condition;

[0063] The equipment participating in the test includes the primary circuit main equipment, charging pump, hydrostatic test pump, and letdown regulating valve;

[0064] Step 1-2: Connect the frequency converter cable of a charging pump to the strength hydrostatic test pump, and conduct a trial run on the strength hydrostatic test pump to ensure that the frequency converter is available;

[0065] Step 1-3: Check and close all valves and channels at the primary circuit hydrostatic test boundary to ensure that the pressure will not leak to other systems during the test;

[0066] Step 2: Complete the system online according to the hydrostatic test boundary, and conduct the primary circuit hydrostatic test under cold conditions;

[0067] Specifically, it includes:

[0068] Step 2-1: Charge the primary circuit and conduct sufficient exhaust to ensure that the primary circuit is completely filled;

[0069] Step 2-2: Use the charging pump to inject coolant into the primary circuit, raise the primary circuit pressure to the 3.2 MPa platform at a speed not exceeding 0.98 MPa / min, and conduct leak detection;

[0070] Step 3: Heat the primary circuit to the hydrostatic test temperature;

[0071] Specifically, it includes:

[0072] Step 3-1: After the cold test is completed, lower the primary circuit pressure and liquid level, and charge nitrogen into the pressurizer to ensure the suction head for starting the main pump;

[0073] The primary circuit pressure drops to 1.5 - 1.8 Mpa;

[0074] Step 3-2: Short-time start the reactor primary coolant pump to conduct dynamic exhaust of the primary circuit to ensure that the non-condensable gas in the primary circuit equipment and pipelines is fully discharged;

[0075] Step 3-3: Restart the reactor primary coolant pump to heat the primary loop to the hydrostatic test temperature to prevent cold embrittlement of the equipment;

[0076] The hydrostatic test temperature is not lower than 115 °C;

[0077] Step 4: Hydrostatic strength test of the primary loop;

[0078] Specifically, it includes:

[0079] Step 4-1: Stop the reactor primary coolant pump and the residual heat removal system;

[0080] Step 4-2: Drain the nitrogen in the pressurizer, restore the hydrostatic test boundary according to the program requirements, and refill the primary loop main equipment and the connected pipelines;

[0081] Step 4-3: Use a temporary device to lock the pressurizer safety valve group to prevent the pressurizer safety valve from operating during the hydrostatic test;

[0082] Step 4-4: Gradually increase the primary loop pressure to each test pressure platform and maintain it. During this period, control the pressure increase rate of the primary loop not to exceed the limit, and at the same time conduct leak detection;

[0083] Specifically, adjust the charging pump to increase the primary loop pressure to test platforms such as 3.2 MPa, 9.8 MPa, 15.7 MPa, 17.6 MPa, etc. at a rate not exceeding 0.98 MPa / min and maintain the pressure for leak detection;

[0084] During the hydrostatic test of the primary loop, control the feed water temperature of the steam generator and the main steam discharge of the secondary loop to ensure that the primary loop coolant temperature is within the range required for the hydrostatic test;

[0085] Step 4-5: Use a temporary frequency converter to gradually increase the outlet flow of the strength hydrostatic test pump, raise the primary loop pressure to the strength hydrostatic test platform. During this period, control the pressure increase rate of the primary loop not to exceed the limit, maintain for 10 - 20 min and then reduce the pressure to the leak detection platform for leak detection;

[0086] The temporary frequency converter adjusts the frequency of the primary loop strength hydrostatic test pump to continue increasing the primary loop pressure to the 22 MPa strength hydrostatic test platform at a rate not exceeding 0.98 MPa / min;

[0087] Step 5: Reduce the primary loop pressure to 12 MPa and cooperate with the strength hydrostatic test of the secondary loop;

[0088] Specifically, it includes:

[0089] Step 5-1: Lower the primary loop pressure by adjusting the letdown flow and the frequency of the hydrostatic test pump and cooperate with the strength hydrostatic test of the secondary loop;

[0090] The rate of pressure reduction does not exceed 0.98 MPa / min. After the pressure is reduced to 12 MPa, maintain this pressure;

[0091] Step 5-2: After the strength hydrostatic test of the secondary circuit is completed, continue to reduce the pressure of the primary circuit to the range required by the technical regulations.

[0092] Step 6: Restore the system state after the hydrostatic test and prepare to heat the reactor;

[0093] Specifically include:

[0094] Step 6-1: The primary circuit continues to depressurize to 1.5 - 1.8 MPa and establish a nitrogen cushion in the pressurizer;

[0095] Step 6-2: Restore the operation of the reactor auxiliary system and start the reactor primary coolant pump to heat the reactor to the hot state.

[0096] Through tests, it is proved that for the strength hydrostatic test of the primary circuit, a frequency converter is externally connected to the hydrostatic test pump for the hydrostatic test, avoiding the uncontrollable risk of the primary circuit pressure caused by adjusting the manual valve, greatly reducing the operation difficulty and saving manpower.

[0097] In this strength hydrostatic test of the primary circuit, the average rate of pressure increase and decrease is maintained between 0.2 - 0.4 MPa / min, meeting the requirements of the procedure. The control accuracy of the test pressure is improved from ±0.3 MPa to ±0.05 MPa, significantly reducing the risk of test overpressure. At the same time, the test time is shortened by about 6 h, reducing the waiting time under the high-pressure platform and reducing the potential damage risk of stress to components.

[0098] The present invention uses a temporary device to externally connect a frequency converter to the strength hydrostatic test pump to realize the frequency conversion operation of the hydrostatic test pump and control the pressure increase and decrease rates of the primary circuit;

[0099] The present invention uses a temporary device to block the safety valve at the outlet of the hydrostatic test pump to avoid the misoperation of the safety valve due to overpressure during the test;

[0100] The present invention implements I&C changes to introduce the start-stop logic of the hydrostatic test pump into the frequency converter to ensure that the operation logic of the hydrostatic test pump remains unchanged;

[0101] The present invention uses a temporary device to lock the safety valve group of the pressurizer to avoid the loss of water in the primary circuit caused by the action of the safety valve and reduce the damage to the safety valve group components during the hydrostatic test;

[0102] The present invention uses the method of establishing a nitrogen cushion in the pressurizer to ensure the suction head of the primary coolant pump, start the primary coolant pump to heat the primary circuit coolant, and increase the coolant heating rate;

[0103] In the experiment of the present invention, the cooling of the primary coolant is controlled by the feed water temperature of the steam generator and the main steam discharge amount of the secondary circuit, so as to avoid the misoperation of the protection caused by the continuous heating of the residual heat of the reactor during the experiment.

[0104] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0105] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for the strength hydrostatic test of the primary circuit of a nuclear power unit, characterized in that, It includes the following steps: Step 1: Prepare the equipment participating in the test; Step 2: Complete the system online according to the hydrostatic test boundary and conduct a hydrostatic test on the primary loop under cold conditions; Step 3: Reduce the pressure and liquid level of the primary loop, establish a nitrogen cushion in the pressurizer, exhaust, and then start the main pump to heat the primary loop to the hydrostatic test temperature; Step 4: The frequency converter adjusts the charging pump to gradually increase the pressure of the primary loop to each test platform for leak detection. Then, use the frequency converter to gradually increase the outlet flow of the intensity hydrostatic test pump, raise the pressure of the primary loop to the pressure of the intensity hydrostatic test platform, and then reduce the pressure to the leak detection platform for leak detection; Step 5: The primary loop reduces pressure and cooperates with the intensity hydrostatic test of the secondary loop; Step 6: After the hydrostatic test, restore the system state and prepare to heat the reactor.

2. The method for the strength hydrostatic test of the primary circuit of a nuclear power unit according to claim 1, wherein The specific content of Step 1 includes: Step 1-1: Confirm that the equipment participating in the test is in good condition; The equipment participating in the test includes primary loop main equipment, charging pump, hydrostatic test pump, and letdown regulating valve; Step 1-2: Connect the frequency converter cable of one charging pump to the intensity hydrostatic test pump and conduct a trial run on the intensity hydrostatic test pump to ensure that the frequency converter is available; Step 1-3: Check and close all valves and channels of the primary loop hydrostatic test boundary to ensure that the pressure will not leak to other systems during the test.

3. The method for the strength hydraulic test of the primary circuit of a nuclear power unit according to claim 1, characterized in that, The specific content of Step 2 includes: Step 2-1: Fill the primary loop and conduct sufficient exhaust to ensure that the primary loop is completely filled; Step 2-2: Use the charging pump to inject coolant into the primary loop and raise the pressure of the primary loop to the 3.2 MPa platform at a speed not exceeding 0.98 MPa / min, and conduct leak detection.

4. The method for the strength hydrostatic test of the primary circuit of a nuclear power unit according to claim 1, characterized in that The specific content of Step 3 includes: Step 3-1: After the cold test is completed, reduce the pressure and liquid level of the primary loop, and charge nitrogen into the pressurizer to ensure the suction head for starting the main pump; Step 3-2: Start the reactor primary coolant pump briefly for dynamic exhaust of the primary loop to ensure that the non-condensable gas in the primary loop equipment and pipelines is fully discharged; Step 3-3: Start the reactor primary coolant pump again to heat the primary loop to the hydrostatic test temperature to prevent cold embrittlement of the equipment.

5. The method for the strength hydrostatic test of the primary circuit of a nuclear power unit according to claim 4, wherein The pressure of the primary loop drops to 1.5 - 1.8 Mpa; the hydrostatic test temperature is not lower than 115 °C.

6. The method for the strength hydrostatic test of the primary circuit of a nuclear power unit according to claim 1, characterized in that, The specific content of Step 4 includes: Step 4-1: Stop the reactor primary coolant pump and the residual heat removal system; Step 4-2: Drain the nitrogen in the pressurizer, restore the hydrostatic test boundary according to the procedure requirements, and refill the primary loop main equipment and the connected pipelines; Step 4-3: Use a temporary device to lock the pressurizer safety valve group to avoid the action of the pressurizer safety valve during the hydrostatic test; Step 4-4: Adjust the charging pump to increase the pressure of the primary loop to each test pressure platform at a speed not exceeding 0.98 MPa / min and maintain it. During this period, control the pressure rise rate of the primary loop not to exceed the limit, and conduct leak detection at the same time; During the hydrostatic test of the primary loop, control the feed water temperature of the steam generator and the main steam discharge of the secondary loop to ensure that the temperature of the primary loop coolant is within the range required for the hydrostatic test; Step 4-5: Gradually increase the outlet flow of the intensity hydrostatic test pump using a temporary frequency converter, and raise the primary circuit pressure to the intensity hydrostatic test platform. During this period, control the pressure increase rate of the primary circuit not to exceed the limit. After maintaining for 10 - 20 minutes, reduce the pressure to the leak detection platform for leak detection.

7. The method for the strength hydrostatic test of the primary circuit of a nuclear power unit according to claim 6, characterized in that, In the said step 4-4, there are 4 test pressure platforms, and the pressures of each test platform are 3.2 MPa, 9.8 MPa, 15.7 MPa, and 17.6 MPa respectively.

8. The method for the strength hydrostatic test of the primary circuit of a nuclear power unit according to claim 6, wherein, In the said step 4-5, the temporary frequency converter adjusts the frequency of the intensity hydrostatic test pump of the primary circuit to continue raising the primary circuit pressure to the 22 MPa intensity hydrostatic test platform at a rate not exceeding 0.98 MPa / min.

9. The method for the strength hydrostatic test of the primary circuit of a nuclear power unit according to claim 1, wherein The said step 5 specifically includes: Step 5-1: By adjusting the letdown flow and the frequency of the hydrostatic test pump, reduce the primary circuit pressure to 12 MPa at a rate not exceeding 0.98 MPa / min, then maintain this pressure and cooperate with the secondary circuit intensity hydrostatic test. Step 5-2: After the secondary circuit intensity hydrostatic test is completed, continue to reduce the primary circuit pressure to the range required by the technical regulations.

10. The method for the strength hydrostatic test of the primary circuit of a nuclear power unit according to claim 1, wherein The said step 6 specifically includes: Step 6-1: The primary circuit continues to depressurize to 1.5 - 1.8 MPa and establish a nitrogen cushion in the pressurizer. Step 6-2: Resume the operation of the reactor auxiliary system, start the reactor primary coolant pump to heat the reactor to the hot state.

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