Automatic control method for nitrogen purging of key equipment in primary circuit of nuclear power plant

Abstract

This invention belongs to the field of nuclear power plant reactor operation and automatic control technology, specifically relating to an automatic control method for nitrogen purging of key primary circuit equipment in a nuclear power plant. It includes: Step 1: Opening the electric valve of the emergency exhaust manifold to the hydrogen combustion system; Step 2: Monitoring and determining whether to perform nitrogen purging of the key primary circuit equipment; Step 3: Starting nitrogen purging; Step 4: Timing for 30 minutes; Step 5: Changing the purging direction; Step 6: Timing for 30 minutes, then returning to Step 3; Step 7: Monitoring that the pressure measured by the reactor core outlet pressure gauge is less than 0.1 MPa, closing the electric valves of the emergency exhaust manifold to the hydrogen combustion system, the low-pressure nitrogen supply valve to the reactor pressure vessel, the steam generator emergency exhaust valve, the pressurizer emergency exhaust valve, and the reactor pressure vessel emergency exhaust valve, restoring the initial state. The beneficial effect is that this invention completely avoids the operation of releasing hydrogen and radioactive gases into the reactor building.

Description

Technical Field

[0001] This invention belongs to the field of nuclear power plant reactor device operation and automatic control technology, specifically relating to an automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant. Background Technology

[0002] Before the reactor pressure vessel of a pressurized water reactor nuclear power plant is desealed and opened (during the transition from "cold state" to "maintenance cold shutdown"), when the reactor liquid level drops to the central axis of the hot section, low-pressure nitrogen needs to be introduced to purge the space under the top cover of the reactor pressure vessel and the steam generator manifold to reduce the hydrogen concentration and prevent hydrogen from accumulating and concentrating locally in key equipment of the primary loop to reach explosive concentrations.

[0003] Traditional nitrogen purging of critical primary circuit equipment is manually controlled, and the purged gas is directly discharged into the reactor building lobby. During nitrogen purging, operators must manually operate numerous electric valves while closely monitoring critical parameters such as hydrogen concentration and dose levels in the reactor lobby, radioactivity instruments at the exhaust fan inlet and outlet, and ARMS radiation monitoring instruments in the exhaust stack. The operators have to monitor numerous parameters and bear a heavy workload. Furthermore, the discharge of purged gas into the reactor building lobby poses a risk of localized hydrogen explosions and uncontrolled radioactive releases, potentially leading to reported operational events. Summary of the Invention

[0004] The purpose of this invention is to provide an automated control method for nitrogen purging of critical primary circuit equipment in nuclear power plants. Traditional nitrogen purging methods for critical primary circuit equipment are manual, requiring operators to monitor numerous parameters and bear a heavy workload during purging, and carrying the risk of localized hydrogen explosions or uncontrolled releases of radioactive materials, leading to operational incident reports. This invention provides an automated control method for nitrogen purging of critical primary circuit equipment in nuclear power plants, avoiding human error and the release of hydrogen and radioactive gases into the reactor building, effectively controlling risks, and improving the efficiency and safety of nitrogen purging.

[0005] The technical solution of the present invention is as follows: An automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant, wherein before the reactor pressure vessel is unsealed and the cover is removed, when the reactor liquid level drops to the central axis of the hot section, a purging time is set and the following steps are executed to perform nitrogen purging of the key equipment in the primary loop, specifically including: Step 1: Open the emergency exhaust manifold to the electric valve of the hydrogen combustion system, then proceed to Step 2; Step 2: Monitor and determine whether to perform nitrogen purging of critical primary circuit equipment; Step 3: Begin nitrogen purging; Step 4: Set the timer, and proceed to Step 5 after the timer expires; Step 5: Change the flow direction and purge; Step 6: Set the timer, and after it ends, proceed to Step 3; Step 7: If the pressure measured by the reactor core outlet pressure gauge is less than 0.1 MPa, close the electric valve of the emergency exhaust manifold to the hydrogen combustion system, and restore the electric valves supplying low-pressure nitrogen to the reactor pressure vessel, the steam generator emergency exhaust electric valve, the pressurizer emergency exhaust electric valve, and the reactor pressure vessel emergency exhaust electric valve to their initial states.

[0006] If the pressure measured by the reactor core outlet pressure gauge in step 2 is less than 0.1 MPa, proceed to step 3.

[0007] In step 3, the electric valve supplying low-pressure nitrogen to the reactor pressure vessel is opened.

[0008] In step 3, the pressurizer emergency exhaust electric valve that supplies low-pressure nitrogen to the reactor pressure vessel is opened.

[0009] In step 3, the emergency exhaust electric valve of the steam generator supplying low-pressure nitrogen to the reactor pressure vessel is opened, and the process proceeds to step 4.

[0010] In step 5, the electric valve supplying low-pressure nitrogen to the reactor pressure vessel is closed, the electric valve supplying low-pressure nitrogen to the steam generator is opened, the emergency exhaust valve of the steam generator is closed, the emergency exhaust valve of the reactor pressure vessel is opened, and then the process proceeds to step 6.

[0011] In step 6, steps 3 to 6 are repeated. If the total purging time meets the preset time, proceed to step 7.

[0012] The beneficial effects of this invention are as follows: This invention completely avoids the operation of releasing hydrogen and radioactive gases into the reactor building; reduces the risk of radioactive gas release into the environment; reduces the risk of local hydrogen explosions within the reactor building; and reduces the difficulty of manual operation by operators through automatic control, thus reducing the possibility of human error. Attached Figure Description

[0013] Figure 1 This is a simplified diagram of the nitrogen purging process for a key piece of equipment in the primary loop of a nuclear power plant.

[0014] In the diagram: 1 Reactor pressure vessel; 2 Steam generator manifold; 3 Pressurizer; 4 Pressure relief tank; 5 Hydrogen combustion system; 6, 7: Low-pressure nitrogen system; 8 Reactor building lobby; 9 Emergency exhaust valve for reactor pressure vessel; 10 Emergency exhaust valve for pressurizer; 11 Emergency exhaust valve for steam generator; 12 Electric valve supplying low-pressure nitrogen to steam generator; 13 Electric valve from emergency exhaust manifold to hydrogen combustion system; 14 Electric valve from emergency exhaust manifold to reactor building lobby; 15 Electric valve from emergency exhaust manifold to pressure relief tank; 16 Hot section centerline; 17 Emergency exhaust manifold for critical equipment; 18 Reactor core outlet pressure gauge; 19 Electric valve supplying low-pressure nitrogen to reactor pressure vessel. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] This invention provides an automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant. It has the advantages of automatic step-by-step operation, precise control, and real-time monitoring of the hydrogen concentration of the purging gas. At the same time, the equipment exhaust is directly discharged into the hydrogen combustion system (KPL), which completely avoids the release of hydrogen and radioactive gases into the reactor building, effectively controls the risks during purging, and improves purging efficiency.

[0017] An automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant is proposed, and the solution adopted is as follows: Design and apply an automatic control program for nitrogen purging of critical equipment, which can automatically determine whether the primary circuit pressure allows the execution of nitrogen purging of critical equipment and has inherent safety. The program was optimized to set the purging path, and the nitrogen purging gas for the key equipment in the primary loop was discharged to the hydrogen combustion system through the emergency exhaust system, which avoided the release of hydrogen and radioactive gases into the reactor building hall and reduced the risk of local hydrogen explosions and the release of radioactive gases into the environment within the reactor building. The program can collect the hydrogen concentration of the gas after purging in real time. The program determines that purging is complete based on the set venting time or manual sampling results, and automatically places the system in its initial state.

[0018] like Figure 1 As shown, an automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant is described. Before the reactor pressure vessel 1 is unsealed and the cover is removed, when the reactor liquid level drops to the central axis 16 of the hot section, a purging time is set and the following steps are executed to purge the key equipment in the primary loop with nitrogen. Specifically, the method includes: Step 1: Open the emergency exhaust manifold to the hydrogen combustion system electric valve 13, then proceed to Step 2; Step 2: Monitor and determine whether to perform nitrogen purging of critical primary circuit equipment; If the pressure measured by pressure gauge 18 at the reactor core outlet is less than 0.1 MPa, proceed to step 3. Nitrogen parameters: Concentration (by volume) not less than 99.6%; Oxygen content (by volume) not more than 0.4%; Water vapor content not more than 0.07 g / m³ 3 Temperature: 20-40℃; Pressure: 0.98±0.005 MPa; Flow rate: 6.5~7.5 Nm³ 3 / h.

[0019] Step 3: Begin nitrogen purging; Open the electric valve 19 for supplying low-pressure nitrogen to the reactor pressure vessel, the electric valve 10 for emergency exhaust of the pressurizer, and the electric valve 11 for emergency exhaust of the steam generator, and proceed to step 4. Step 4: Set a timer for 30 minutes, then proceed to Step 5; Step 5: Change the flow direction and purge; Close the electric valve 19 for supplying low-pressure nitrogen to the reactor pressure vessel, open the electric valve 12 for supplying low-pressure nitrogen to the steam generator, close the electric valve 11 for emergency exhaust from the steam generator, open the electric valve 9 for emergency exhaust from the reactor pressure vessel, and proceed to step 6. Step 6: Time for 30 minutes. After the time is up, go to step 3. Repeat steps 3 to 6. If the total purging time meets the preset time, go to step 7. Step 7: If the pressure measured by the reactor core outlet pressure gauge 18 is less than 0.1 MPa, close the electric valve 13 of the emergency exhaust manifold to the hydrogen combustion system, the electric valve 19 of the low-pressure nitrogen supply to the reactor pressure vessel, the electric valve 11 of the steam generator emergency exhaust, the electric valve 10 of the pressurizer emergency exhaust, and the electric valve 9 of the reactor pressure vessel emergency exhaust. The system is then restored to its initial state.

[0020] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. An automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant, characterized in that: Before unsealing and removing the cover from the reactor pressure vessel, when the reactor liquid level drops to the central axis of the hot section, a purging time is set and the following steps are performed to purge the critical primary circuit equipment with nitrogen, specifically including: Step 1: Open the emergency exhaust manifold to the electric valve of the hydrogen combustion system, then proceed to Step 2; Step 2: Monitor and determine whether to perform nitrogen purging of critical primary circuit equipment; Step 3: Begin nitrogen purging; Step 4: Set the timer, and proceed to Step 5 after the timer expires; Step 5: Change the flow direction and purge; Step 6: Set the timer, and after it ends, proceed to Step 3; Step 7: If the pressure measured by the reactor core outlet pressure gauge is less than 0.1 MPa, close the electric valve of the emergency exhaust manifold to the hydrogen combustion system, and restore the electric valves supplying low-pressure nitrogen to the reactor pressure vessel, the steam generator emergency exhaust electric valve, the pressurizer emergency exhaust electric valve, and the reactor pressure vessel emergency exhaust electric valve to their initial states.

2. The automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant as described in claim 1, characterized in that: If the pressure measured by the reactor core outlet pressure gauge in step 2 is less than 0.1 MPa, proceed to step 3.

3. The automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant as described in claim 1, characterized in that: In step 3, the electric valve supplying low-pressure nitrogen to the reactor pressure vessel is opened.

4. The automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant as described in claim 3, characterized in that: In step 3, the pressurizer emergency exhaust electric valve that supplies low-pressure nitrogen to the reactor pressure vessel is opened.

5. The automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant as described in claim 4, characterized in that: In step 3, the emergency exhaust electric valve of the steam generator supplying low-pressure nitrogen to the reactor pressure vessel is opened, and the process proceeds to step 4.

6. The automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant as described in claim 1, characterized in that: In step 5, the electric valve supplying low-pressure nitrogen to the reactor pressure vessel is closed, the electric valve supplying low-pressure nitrogen to the steam generator is opened, the emergency exhaust valve of the steam generator is closed, the emergency exhaust valve of the reactor pressure vessel is opened, and then the process proceeds to step 6.

7. The automatic control method for nitrogen purging of key equipment in the primary loop of a nuclear power plant as described in claim 1, characterized in that: In step 6, steps 3 to 6 are repeated. If the total purging time meets the preset time, proceed to step 7.

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