A pressurized water reactor automatic depressurization system

Abstract

This invention belongs to the technical field of nuclear reactor systems, specifically relating to an automatic depressurization system for a pressurized water reactor. It includes four stages of depressurization valves. The first three stages are connected to the pressurizer steam chamber and share a connecting pipe with two of the three pressurizer safety valves. The discharge from the first three stages is collected and then enters the depressurization water pool inside the containment via a sprayer, and is subsequently discharged into the containment through the depressurization water pool. The automatic depressurization system proposed in this invention has a simpler configuration, reduces the number of devices by 20%, has higher reliability, simplifies operation, and reduces the power supply load. The fourth stage uses an electric valve instead of the explosion valve in units such as the AP1000, meeting the start-up and operation requirements of the passive safety injection system and improving the safety of the nuclear power unit.

Description

Technical Field

[0001] This invention belongs to the field of nuclear reactor system technology, specifically relating to an automatic depressurization system for a pressurized water reactor. Background Technology

[0002] To ensure the safe operation of pressurized water reactor nuclear power units, safety injection systems (such as AP1000 and Hainan Changjiang small modular reactor) are installed to cool the reactor core in emergencies, maintaining the integrity of the fuel cladding and protecting public health and safety. To ensure the reliability of the safety injection system, it is typically designed to operate passively, requiring no active equipment such as pumps, fans, or AC power supplies, relying solely on passive equipment and processes such as gravity injection and compressed gas expansion.

[0003] To meet the overall requirements of fully passive design under the Design Basis Condition (DBA) of pressurized water reactor nuclear power plants, ensure the smooth operation of the passive safety injection system, and provide long-term cooling for the reactor core, an automatic depressurization system (ADS) is implemented. The ADS works in conjunction with the passive safety injection system to perform safety functions. In the event of a hypothetical design basis accident, the ADS must be activated to depressurize the reactor coolant system, allowing the passive safety injection system to smoothly inject water into the reactor core for passive cooling and mitigate the consequences of the accident. To ensure the smooth operation of the passive safety injection system, the ADS design must possess high reliability and meet the single failure criterion. Therefore, nuclear power projects such as AP1000 and Hainan Changjiang small modular reactor (SMR) have designed their ADS with four stages and a total of 20 valves. The system is complex, requires a large power supply load, and the fourth-stage ADS valves are rupture valves, posing safety hazards, high costs, and non-reusability. To address the aforementioned issues and further improve the reliability of automatic depressurization systems, this invention proposes an automatic depressurization system for pressurized water reactors. This system simplifies system configuration, enhances system reliability, and improves the safety of nuclear power units while meeting the startup and operation requirements of passive safety injection systems. Summary of the Invention

[0004] The purpose of this invention is to provide an automatic depressurization system for pressurized water reactors, which has a simpler configuration, reduces the number of devices by 20%, has higher reliability, simplifies the operation mode, reduces the power supply load, and uses electric valves in the fourth stage instead of the explosion valves of AP1000 and other units, meeting the start-up and operation requirements of the passive safety injection system and improving the safety of nuclear power units.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] An automatic depressurization system for pressurized water reactors includes four stages of depressurization valves. The first three stages of depressurization valves are connected to the pressurizer steam chamber and share a pipe with two of the three pressurizer safety valves. The discharge from the first three stages of depressurization valves is collected and then enters the depressurization water pool inside the containment via a sprayer, and is discharged into the containment through the depressurization water pool.

[0007] Each of the four pressure relief valves has a redundant design.

[0008] Each of the first three stages of the pressure relief valve has two columns, A and B, and the arrangement of series A and series B is the same.

[0009] The first-stage automatic pressure relief function of Series A is performed by a single pressure regulator pilot-operated safety valve RCS018VP.

[0010] The Series A second-stage pressure relief valve includes one normally closed electric gate valve RCS421VP and one normally closed electric stop valve RCS423VP, arranged in series.

[0011] The Series A third-stage pressure relief valve includes one normally closed electric gate valve RCS431VP and one normally closed electric stop valve RCS433VP, arranged in series.

[0012] The fourth-stage pressure relief valve is set in three rows, with each row consisting of two normally closed electric gate valves connected in series, which are respectively connected to the hot section of the main pipelines #1, #2, and #3.

[0013] Normally closed electric gate valves RCS441VP and RCS442VP are connected to the hot section of main pipeline #1, and normally closed electric gate valves RCS443VP and RCS444VP are connected to the hot section of main pipeline #2.

[0014] Normally closed electric gate valves RCS445VP and RCS446VP are connected to the hot section of the No. 3 main pipeline and are directly discharged into the atmosphere inside the containment when pressure is released.

[0015] When the water level in the replenishment tank drops by 1, the first-stage pressure relief valve is automatically opened 5 seconds later. 50 seconds after the first-stage pressure relief valve opens, the second-stage pressure relief valve is triggered to open. 120 seconds after the second-stage pressure relief valve opens, the third-stage pressure relief valve is triggered to open. When the water level in the replenishment tank drops by 2, the fourth-stage pressure relief valve is triggered to open 60 seconds after the third-stage pressure relief valve opens.

[0016] The beneficial effects achieved by this invention are as follows:

[0017] The automatic depressurization system proposed in this invention has a simpler configuration, reduces the number of devices by 20%, has higher reliability, simplifies the operation mode, reduces the power supply load, and uses electric valves in the fourth stage instead of the explosion valves of AP1000 and other units, which meets the start-up and operation requirements of the passive safety injection system and improves the safety of nuclear power units. Attached Figure Description

[0018] Figure 1 This is a diagram of an automatic depressurization system for a pressurized water reactor.

[0019] Figure 2 This is the logic diagram for the start signal. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0021] The automatic depressurization system for pressurized water reactors described in this invention mainly comprises four stages of depressurization valves, each with redundant design. The first three stages of automatic depressurization valves are connected to the pressurizer steam chamber and share a connecting pipe with two of the three pressurizer safety valves. After the discharge from the first three stages of depressurization valves is collected, it enters the depressurization water pool inside the containment via a sprayer, and is then discharged into the containment through the depressurization water pool. Each of the first three stages of automatic depressurization valves has two rows (A and B), and series A and series B are arranged identically. The series is described using series A as an example. The first-stage automatic pressure relief function of Series A is performed by a single pressure regulator pilot-operated safety valve (RCS018VP); the second-stage automatic pressure relief valve of Series A includes a normally closed electric gate valve (RCS421VP) and a normally closed electric stop valve (RCS423VP), arranged in series; the third-stage automatic pressure relief valve of Series A includes a normally closed electric gate valve (RCS431VP) and a normally closed electric stop valve (RCS433VP), arranged in series. The fourth-stage pressure relief valve is arranged in three rows, each row including two normally closed electric gate valves connected in series, which are respectively connected to the hot sections of the main pipelines #1, #2, and #3. Among them, normally closed electric gate valves RCS441VP and RCS442VP are connected to the hot section of the main pipeline #1, normally closed electric gate valves RCS443VP and RCS444VP are connected to the hot section of the main pipeline #2, and normally closed electric gate valves RCS445VP and RCS446VP are connected to the hot section of the main pipeline #3. During pressure relief, the valves are directly discharged into the atmosphere inside the containment.

[0022] The automatic pressure relief system for pressurized water reactors described in this invention includes three stages of automatic pressure relief pipelines connected to a pressurizer and located on top of the pressurizer. Ten automatic pressure relief valves (stages 1-3) are arranged in two groups, separated by a steel structure. Each group consists of three parallel paths, one for each stage, with a separate main pipe leading from the top of the pressurizer and another main pipe directing the exhaust steam to its respective pressure relief nozzle. The fourth stage of automatic pressure relief pipeline is arranged in three rows on the main hot-pipe sections of the three loops. Each row has two electrically operated gate valves; the second valve has no downstream connection, allowing the pressure relief steam to be directly released into the containment atmosphere during pressure relief.

[0023] The first-stage automatic depressurization function of the automatic depressurization system for pressurized water reactors described in this invention is undertaken by the pressurizer safety valve. The pressurizer safety valve primarily provides overpressure protection for the primary circuit. Under conditions that cause an increase in primary circuit pressure, it automatically opens according to a pressure setpoint to prevent primary circuit overpressure. The automatic depressurization function is mainly used for primary circuit depressurization under different fault location and acceleration (LOCA) conditions, enabling the safety injection system to successfully achieve emergency core cooling. These two functions are used in different accident scenarios; the pressurizer safety valve's role in providing the first-stage automatic depressurization function does not affect the original overpressure protection function.

[0024] The automatic depressurization system for pressurized water reactors described in this invention features a fourth-stage depressurization valve arranged in three rows, with each row comprising two normally closed electric gate valves connected in series to the hot section of the main pipeline. The use of electric gate valves in the fourth stage meets the functional requirements of the automatic depressurization system, significantly reduces costs, and provides more mature, reliable, and safer valves that can be reused.

[0025] In the automatic depressurization system for pressurized water reactors described in this invention, when a LOCA accident occurs in the RCS system and passive safety injection is required, the core makeup water tank of the passive core cooling system is activated first, and the automatic depressurization system automatically opens step by step according to the corresponding signals. Besides automatic activation upon activation signal, the operator can also manually activate it. The actions, activation signals, and activation times for each stage are as follows: 5 seconds after the makeup water tank level drops below 1 level, the first-stage depressurization valve is automatically activated; 50 seconds after the first-stage depressurization valve opens, the second-stage depressurization valve opens; 120 seconds after the second-stage depressurization valve opens, the third-stage depressurization valve opens; 60 seconds after the makeup water tank level drops below 2 levels and the third-stage depressurization valve opens, the fourth-stage depressurization valve opens.

[0026] In the automatic depressurization system for pressurized water reactors described in this invention, all equipment and pipelines are redundantly designed. Each of the first three automatic depressurization valves has two rows, and the fourth-stage depressurization valve has three rows. The system design meets the single fault criterion, and the automatic depressurization valves meet the operation and qualification requirements under the design baseline accident conditions.

[0027] An automatic depressurization system for pressurized water reactors according to the present invention is shown in the schematic diagram below. Figure 1 As shown.

[0028] The automatic depressurization system for pressurized water reactors described in this invention mainly includes four stages of depressurization valves. The first, second, and third stages of automatic depressurization pipelines are connected to the pressurizer and are located on top of the pressurizer. The fourth stage of automatic depressurization pipeline is divided into three rows, arranged on the main hot pipe sections of the three loops. When a LOCA accident occurs in the RCS system requiring passive safety injection, the core makeup water tank of the passive core cooling system is activated first, and the automatic depressurization system automatically opens stage by stage according to the corresponding signals. The actions and activation signals for each stage are shown in Table 1. The activation signal logic is as follows: Figure 2 As shown.

[0029] In the event of a LOCA (Lowest Response Capacity) accident, the safety injection system needs to be activated for emergency cooling of the primary circuit to ensure the water level in the reactor core and long-term cooling. The safety injection system mainly relies on the full-pressure makeup water tank and the external high-level water tank to achieve high-pressure and low-pressure safety injection, respectively. Due to the limitations of the high-pressure safety injection water volume and the low-pressure safety injection head, for minor LOCA conditions, an automatic depressurization subsystem is required to depressurize the primary circuit, thereby effectively connecting the high, medium, and low-pressure safety injection.

[0030] According to the requirements of small LCOA accidents, when the water level in the total pressure water supply tank drops to the corresponding set value, the automatic pressure relief subsystem is put into operation. Before the total pressure water supply tank is emptied, the valves at each level of the automatic pressure relief valve are opened in sequence, so as to achieve complete pressure relief of the primary loop system, thereby enabling the low-pressure safety injection of the high-level water tank outside the shell to be effectively injected into the primary loop.

[0031] For large LOCA conditions, the primary circuit system can be completely depressurized by relying on the breach. The automatic depressurization subsystem will still be triggered during the accident, but it is not a restrictive condition.

[0032] For non-LOCA accidents such as main steam pipeline rupture or steam generator heat transfer tube rupture, although the full-pressure water tank of the safety injection system will be put into operation, the cooling of the passive waste heat discharge system will not cause the liquid level of the full-pressure water tank to drop to the set value that triggers the automatic pressure relief subsystem, so the system does not need to be put into operation.

[0033] The first-stage automatic depressurization function of the automatic depressurization system for pressurized water reactors described in this invention is undertaken by the pressurizer safety valve. Because the automatic depressurization subsystem needs to perform safety functions, the isolation valves at each stage of the system must meet the functional level 1 requirements, resulting in high cost per valve. Furthermore, due to reliability and availability requirements under accident conditions for the safety / dedicated system, each stage of the automatic depressurization subsystem requires at least two redundant rows; if conventional isolation valves are used, each row would require two isolation valves. Using the pressurizer safety valve for the first-stage automatic depressurization function can correspondingly reduce the number of first-stage depressurization valves in the four automatic depressurization systems. Given the current overall layout of the reactor building, the space at the top of the pressurizer is limited. Using the pressurizer safety valve as the first-stage automatic depressurization effectively reduces the number of valves and the number and length of depressurization pipelines at the top of the pressurizer, effectively reducing the arrangement pressure of the depressurization pipelines at the top of the pressurizer. Furthermore, by directly reducing the number of first-stage depressurization valves in the four RPPS systems, the power supply load of the safety-grade DC power supply system can be effectively reduced.

[0034] The automatic depressurization system for pressurized water reactors described in this invention features a fourth-stage depressurization valve system with three rows, each row comprising two normally closed electric gate valves connected in series to the hot section of the main pipeline. The fourth stage utilizes electric gate valves. Compared to the burst valves used in units such as the AP1000, the CDF (probability of core meltdown) calculated using the Risk Spectrum program is 2.15E-7 for the AP1000 RS model, while the CDF value obtained using the scheme described in this invention is 2.15E-7, thus offering higher safety. Furthermore, electric valves are more technologically mature, lower in cost, and reusable than burst valves.

[0035] The automatic depressurization system for pressurized water reactors described in this invention activates the core makeup water tank of the passive core cooling system first when a LOCA accident occurs in the RCS system and passive safety injection is required. The automatic depressurization system then automatically activates step-by-step based on corresponding signals. Besides automatic activation upon activation signal, the operator can also manually activate the system.

[0036] In the automatic depressurization system for pressurized water reactors described in this invention, all equipment and pipelines are redundantly designed. Each of the first three automatic depressurization valves has two rows, and the fourth-stage depressurization valve has three rows. The system design meets the single fault criterion, and the automatic depressurization valves meet the operation and qualification requirements under the design baseline accident conditions.

[0037] This invention discloses an automatic depressurization system for pressurized water reactors, comprising four stages of depressurization valves. The first, second, and third stages of automatic depressurization pipelines are connected to the pressurizer and are located on top of the pressurizer. The fourth stage of automatic depressurization pipelines is divided into three rows, each arranged on the main pipeline heat pipe section of one of the three loops. The system configuration of this invention is simpler, reducing the number of devices by 20% compared to existing nuclear power units such as the AP1000, resulting in higher reliability, simplified operation, and reduced power supply load. The fourth stage uses an electric valve instead of the burst valves of units like the AP1000, meeting the start-up and operation requirements of the passive safety injection system and improving the safety of the nuclear power unit.

[0038] This invention includes four levels of pressure relief valves, fully ensuring the start-up and operation requirements of the passive safety injection system and improving the safety of nuclear power units. The first, second, and third level automatic pressure relief pipelines are connected to the pressurizer, while the fourth level automatic pressure relief pipeline is arranged on the main pipeline hot pipe section of the three loops. The first level automatic pressure relief function is handled by the pressurizer safety valve, reducing the number of valves by four compared to similar systems in existing nuclear power units such as AP1000, resulting in fewer pieces of equipment. The first level automatic pressure relief is divided into two rows, each executed by a pressurizer pilot-operated safety valve, satisfying the single fault criterion. The first level automatic pressure relief function being handled by the pressurizer safety valve reduces the power supply load. The system flow is further simplified by having the first level automatic pressure relief function handled by the pressurizer safety valve. This effectively reduces the number of valves and the number and length of the pressure relief pipeline at the top of the pressurizer, effectively alleviating the arrangement pressure of the pressure relief pipeline at the top of the pressurizer due to limited space. The second-stage automatic pressure relief valves consist of two rows, each containing one normally closed electrically operated gate valve and one normally closed electrically operated shut-off valve, arranged in series to meet the single-failure criterion. The third-stage automatic pressure relief valves also consist of two rows, each containing one normally closed electrically operated gate valve and one normally closed electrically operated shut-off valve, arranged in series to meet the single-failure criterion. The fourth-stage automatic pressure relief valves consist of three rows, each containing two normally closed electrically operated gate valves connected in series, connected to the hot sections of the 1#, 2#, and 3# main pipelines respectively. During pressure relief, the valves directly release pressure into the atmosphere within the containment, effectively ensuring the maximum pressure relief capacity requirement while meeting the single-failure criterion. In the event of a LOCA accident in the RCS system requiring passive safety injection, the passive core cooling system... The reactor core makeup water tank is put into operation first, and the automatic depressurization system automatically opens step by step according to the corresponding signals. When a LOCA accident occurs in the RCS system and passive safety injection is required, the operator can manually operate the valves of the automatic depressurization system. It should include at least 3 stages of depressurization valves. The combination of 124 and 134 stages of depressurization valves in the aforementioned 4-stage depressurization system can be used according to the actual situation of the nuclear power plant, or a combination of more than 4 stages of depressurization valves can be used. All equipment and pipelines are designed with redundancy. Each of the first three stages of automatic depressurization valves has two rows, and the fourth stage of depressurization valves has three rows. The system design meets the single fault criterion, and the automatic depressurization valves meet the operation and qualification requirements under the design basis accident condition.

[0039] Table 1 Automatic pressure relief operation under accident conditions

[0040]

Claims

1. An automatic depressurization system for a pressurized water reactor, characterized in that: It includes four stages of pressure relief valves. The first three stages of pressure relief valves are connected to the steam chamber of the pressure regulator and share a pipe with two of the three pressure regulator safety valves. After the discharge from the first three stages of pressure relief valves is collected, it enters the pressure relief water pool inside the containment through the sprayer and is discharged into the containment through the pressure relief water pool inside the containment.

2. The automatic depressurization system for pressurized water reactors according to claim 1, characterized in that: Each of the four pressure relief valves has a redundant design.

3. The automatic depressurization system for pressurized water reactors according to claim 1, characterized in that: Each of the first three stages of the pressure relief valve has two columns, A and B, and the arrangement of series A and series B is the same.

4. The automatic depressurization system for pressurized water reactors according to claim 3, characterized in that: The first-stage automatic pressure relief function of Series A is performed by a single pressure regulator pilot-operated safety valve RCS018VP.

5. The automatic depressurization system for pressurized water reactors according to claim 3, characterized in that: The Series A second-stage pressure relief valve includes one normally closed electric gate valve RCS421VP and one normally closed electric stop valve RCS423VP, arranged in series.

6. The automatic depressurization system for pressurized water reactors according to claim 3, characterized in that: The Series A third-stage pressure relief valve includes one normally closed electric gate valve RCS431VP and one normally closed electric stop valve RCS433VP, arranged in series.

7. The automatic depressurization system for pressurized water reactors according to claim 1, characterized in that: The fourth-stage pressure relief valve is set in three rows, with each row consisting of two normally closed electric gate valves connected in series, which are respectively connected to the hot section of the main pipelines #1, #2, and #3.

8. The automatic depressurization system for pressurized water reactors according to claim 7, characterized in that: Normally closed electric gate valves RCS441VP and RCS442VP are connected to the hot section of main pipeline #1, and normally closed electric gate valves RCS443VP and RCS444VP are connected to the hot section of main pipeline #2.

9. The automatic depressurization system for pressurized water reactors according to claim 7, characterized in that: Normally closed electric gate valves RCS445VP and RCS446VP are connected to the hot section of the No. 3 main pipeline and are directly discharged into the atmosphere inside the containment when pressure is released.

10. The automatic depressurization system for pressurized water reactors according to claim 1, characterized in that: When the water level in the replenishment tank drops by 1, the first-stage pressure relief valve is automatically opened 5 seconds later. 50 seconds after the first-stage pressure relief valve opens, the second-stage pressure relief valve is triggered to open. 120 seconds after the second-stage pressure relief valve opens, the third-stage pressure relief valve is triggered to open. When the water level in the replenishment tank drops by 2, the fourth-stage pressure relief valve is triggered to open 60 seconds after the third-stage pressure relief valve opens.

Images