A method for evaluating the availability of an active reactor cavity water injection system combined with a passive one

Abstract

The present invention belongs to the technical field of nuclear power plant safety assessment, and specifically relates to an availability assessment method for an active reactor cavity water injection system combined with a passive one. The method comprises the following steps: 1) drawing a simplified flow chart of a reactor cavity water injection cooling system; 2) constructing a system availability fault tree logic diagram: using AND gates, OR gates, and transfer gates, constructing a system failure fault tree logic diagram according to the simplified flow chart of the reactor cavity water injection cooling system, and the state of the terminal device is used as the basic event of the fault tree; 3) obtaining device status parameters: obtaining the status parameters of each device in the reactor cavity water injection cooling system, the available device is represented by 0, and the unavailable device is represented by 1; 4) by performing logical calculation on the fault tree, when the result is 0, the active reactor cavity water injection cooling system is available; when the result is 1, the active reactor cavity water injection cooling system is unavailable. The present invention saves the time used for evaluation, improves the efficiency of accident decision-making, and the availability evaluation is accurate.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power plant safety assessment, and in particular relates to an availability assessment method for an active reactor cavity water injection system combined with a passive one. Background Art

[0002] The function of the reactor cavity water injection cooling system is to cool the outer wall of the pressure vessel to remove the heat of the core melt, reduce the temperature of the outer wall of the reactor pressure vessel, maintain the integrity of the pressure vessel, retain the core melt in the pressure vessel, and prevent the radioactive melt from leaking into the containment vessel when a serious accident of core melting occurs. Therefore, it is necessary to obtain the equipment operation status of the reactor cavity water injection cooling system in real time.

[0003] According to the provisions of the Severe Accident Management Guidelines (SAMG) for nuclear power plants, the technical support personnel of the power plant are required to manually verify the status of the water supply source, pumps, valves, power supply and other equipment of the reactor cavity water injection cooling system step by step according to the chart in the guidelines, as shown in Table 1, and then comprehensively judge the availability of the system.

[0004]

[0005] The main disadvantages of this method are: (1) it takes a long time to judge and is inefficient; (2) it is time-consuming to obtain the status or availability information of these devices; and (3) it takes up more personnel and energy, and in the event of an accident, more manpower is required.

[0006] Based on the above problems existing in the prior art, it is urgent to design an improved availability evaluation method of active reactor cavity water injection system combined with passive one. Summary of the invention

[0007] The purpose of the present invention is to provide an availability evaluation method for an active reactor cavity water injection system combined with a passive one, so as to obtain a real-time and rapid system availability evaluation under accident conditions and improve the safety level of a nuclear power plant.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for evaluating the availability of an active reactor cavity water injection system combined with a passive one comprises the following steps:

[0010] 1) Draw a simplified flow chart of the reactor cavity water injection cooling system;

[0011] 2) Construct the system availability fault tree logic diagram: Use AND gates, OR gates, and transfer gates to construct the system failure fault tree logic diagram according to the simplified flow chart of the reactor cavity water injection cooling system in step 1), and the status of the terminal equipment is used as the basic event of the fault tree:

[0012] 3) Obtaining equipment status parameters: Obtaining the status parameters of each device in the reactor cavity water injection cooling system through the nuclear power plant information system and data interface. The available equipment is represented by 0, and the unavailable equipment is represented by 1;

[0013] 4) Availability evaluation: By performing logical calculations on the fault tree, when the result is 0, the active cavity water injection cooling system is available; when the result is 1, the active cavity water injection cooling system is unavailable.

[0014] Among them, the reactor cavity water injection cooling system in step 1) includes an active reactor cavity water injection system and a passive reactor cavity water injection system arranged in parallel; the passive reactor cavity water injection system includes a reactor cavity water injection cooling water tank and two passive water injection pipelines; the reactor cavity water injection cooling water tank is connected to the pressure vessel through two passive water injection pipelines arranged in parallel; the cooling water of the reactor cavity water injection cooling water tank relies on gravity to achieve passive reactor cavity injection.

[0015] The active reactor cavity water injection system comprises a refueling water tank, an A-row active water injection pipeline and a B-row active water injection pipeline arranged in parallel; the refueling water tank is connected to the pressure vessel through the A / B-row active water injection pipelines arranged in parallel.

[0016] Each active water injection pipeline includes an electric valve, a check valve, a manual valve, an electric water pump, a normally closed electric valve, a No. 2 check valve, and a No. 2 manual valve, which are connected in sequence. The left side of the electric valve is connected to the refueling water tank, and the right side of the No. 2 manual valve is connected to the pressure vessel. The fire water is connected to the No. 3 manual valve and then connected to the active water injection pipeline.

[0017] Fire water is provided between the check valve and the manual valve of each active water injection pipeline.

[0018] The active reactor cavity water injection system also includes a water injection pump, an AC / DC power supply, and an equipment cooling system.

[0019] In step 3), the initial value of pipeline equipment is set to 0. When the accident site reports that the pipeline is damaged and has lost its function, the status parameter of the pipeline equipment is set to 1; the initial value of the manual valve and check valve is 0, and the status parameter is set to 1 when the equipment is unavailable; the availability of the water tank is determined by the water tank liquid level. When the liquid level is higher than 2.1m, the equipment status is 0; when the liquid level is less than 2.1m, the equipment status is 1, which is considered unavailable.

[0020] In step 2), the fault tree of the active reactor cavity water injection system includes three layers of basic events: the first layer of basic events includes water injection valve failure, refueling water tank water intake failure, and fire water tank water intake failure; the above three basic events are in a logical or relationship.

[0021] The second-level basic events corresponding to the failure of the water injection valve include the failure of the manual valve and the failure of the check valve, which are logically related to each other.

[0022] The second-level basic events corresponding to the failure of water extraction from the refueling water tank include the failure of water extraction from the refueling water tank in column A and the failure of water extraction from the refueling water tank in column B, which are in a logical AND relationship with each other.

[0023] The third-level basic events corresponding to the failure of water intake from the refueling water tank of column A include three basic events with a logical OR relationship with each other: failure of water intake from the refueling water tank of column A, failure of the electric water intake pump of column A, and failure of the pipeline behind the pump of column A; each of the above three basic events is provided with a transfer gate.

[0024] The third-level basic events corresponding to the failure of water intake from the B-train refueling water tank include three basic events with a logical OR relationship between each other: failure of water intake from the B-train refueling water tank, failure of the B-train electric water intake pump, and failure of the pipeline behind the B-train pump; each of the above three basic events is provided with a transfer gate.

[0025] The second-level basic events corresponding to the failure of fire water tank water intake include the failure of fire water tank water intake in column A and the failure of fire water tank water intake in column B, which are logically ANDed to each other. The third-level basic events corresponding to the failure of fire water tank water intake in column A include three basic events with logical OR relationship: failure of fire water tank water intake in column A, failure of electric water intake pump in column A, and failure of pipeline behind pump in column A; each of the above three basic events is provided with a transfer gate. The third-level basic events corresponding to the failure of fire water tank water intake in column B include three basic events with logical OR relationship: failure of fire water tank water intake in column B, failure of electric water intake pump in column B, and failure of pipeline behind pump in column B; each of the above three basic events is provided with a transfer gate.

[0026] The fault tree of the failure of the water intake pipeline of the refueling water tank of column A or column B includes four basic events. The first basic event includes the failure of the refueling water tank, the failure of the electric valve, and the failure of the water intake pipeline, which are logically related to each other.

[0027] The second-level basic events corresponding to the failure of the refueling water tank include the refueling water tank filter blockage and the refueling water tank water level low, which are in a logical AND relationship with each other.

[0028] The second-level basic events corresponding to the failure of the water intake pipeline include manual valve failure, check valve failure, electric valve failure, and pipeline failure, which are logically related to each other.

[0029] The third-level basic events corresponding to the electric valve failure include the electric valve power failure and the electric valve body failure, which are logically ORed to each other. The third-level basic events corresponding to the electric valve power failure include the 380V AC power failure, the 110V DC power failure, and the 48V DC power failure, which are logically ORed to each other.

[0030] The A / B water intake pump failure fault tree includes two levels of basic events. The first level of basic events includes pump body failure, pump power loss, and pump cooling water loss, which are logically related to each other.

[0031] The second-level basic events corresponding to the loss of pump power include the loss of 6.6kV emergency AC power supply and the loss of 110V DC power supply, which are logically OR-related to each other.

[0032] The fault tree for failure of the water intake pipeline after the A or B column pump includes four basic events. The first basic event includes failure of the pipeline valve inside the containment, failure of the pipeline, and failure of the pipeline valve outside the containment, which are logically ORed. The second basic event corresponding to the failure of the pipeline valve inside the containment includes failure of the check valve and failure of the manual valve, which are logically ANDed. The second basic event corresponding to the failure of the pipeline valve outside the containment includes failure of the manual valve, failure of the electric valve of the A / B column, and failure of the check valve, which are logically ORed. The third basic event corresponding to the failure of the electric valve of the A / B column includes failure of the electric valve power supply and failure of the electric valve body, which are logically ORed. The fourth basic event corresponding to the failure of the electric valve power supply includes loss of 380V AC power supply, loss of 110V DC power supply, and loss of 48V DC power supply, which are logically ORed.

[0033] The fault tree of fire water intake pipeline failure in column A or B includes three layers of basic events. The first layer of basic events includes manual valve failure, pipeline failure, and fire water production / distribution system pipeline failure, which are logically ORed to each other. The second layer of basic events corresponding to the fire water production / distribution system pipeline failure include manual valve failure of nuclear island fire water production system and manual valve failure of nuclear island fire water distribution system, which are logically ORed to each other. Manual valve failure of nuclear island fire water production system includes manual valve 1 failure and manual valve No. 3 failure, which are logically ANDed to each other.

[0034] The availability evaluation method of the active reactor cavity water injection system combined with the passive one provided by the present invention can also be used to evaluate the availability of the passive reactor cavity water injection system.

[0035] The beneficial effects achieved by the present invention are:

[0036] 1. Accurate usability evaluation;

[0037] 2. Save the time used for evaluation, improve the efficiency of accident decision-making, and obtain system availability in real time and quickly under accident conditions;

[0038] 3. The evaluation results will help formulate strategies for injecting water into the reactor cavity to mitigate severe accidents;

[0039] 4. The fault tree method adopted is easy to promote and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Methods for confirming the availability of equipment for injecting water into the reactor cavity for existing technologies;

[0041] Figure 2 A flow chart of the availability evaluation method for an active reactor cavity water injection system combined with a passive one;

[0042] Figure 3 Simplified flow chart of the reactor cavity water injection cooling system;

[0043] Figure 4 Fault tree for the active reactor cavity water injection cooling system;

[0044] Figure 5 This is the fault tree for the failure of water intake from the A / B train refueling tank;

[0045] Figure 6 This is the fault tree for the failure of the A / B water intake pump;

[0046] Figure 7 This is the fault tree for the failure of the water intake pipeline after the A / B train pumps;

[0047] Figure 8 This is the fault tree for the failure of the fire water intake pipeline of train A / B;

[0048] Fig. 9 Defines a table for device status parameters.

[0049] In the figure: 11: logic OR gate, 12: basic event, 13: logic AND gate, 14: transfer gate; 1: electric valve, 2: check valve, 3: manual valve, 4: electric water pump, 5: normally closed electric valve. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] like Figure 1 As shown, the present invention provides an availability evaluation method for an active reactor cavity water injection system combined with a passive one, comprising the following steps:

[0052] 1) Draw a simplified flow chart of the reactor cavity water injection cooling system;

[0053] 2) Construct the system availability fault tree logic diagram: Use AND gates, OR gates, and transfer gates to construct the system failure fault tree logic diagram according to the simplified flow chart of the reactor cavity water injection cooling system in step 1), and the status of the terminal equipment is used as the basic event of the fault tree:

[0054] 3) Obtaining equipment status parameters: Obtaining the status parameters of each device in the reactor cavity water injection cooling system through the nuclear power plant information system and data interface. The available equipment is represented by 0, and the unavailable equipment is represented by 1;

[0055] 4) Availability evaluation: By performing logical calculations on the fault tree, when the result is 0, the active cavity water injection cooling system is available; when the result is 1, the active cavity water injection cooling system is unavailable.

[0056] Among them, the reactor cavity water injection cooling system in step 1) includes an active reactor cavity water injection system and a passive reactor cavity water injection system arranged in parallel; the passive reactor cavity water injection system includes a reactor cavity water injection cooling water tank and two passive water injection pipelines; the reactor cavity water injection cooling water tank is connected to the pressure vessel through two passive water injection pipelines arranged in parallel; the cooling water of the reactor cavity water injection cooling water tank relies on gravity to achieve passive reactor cavity injection.

[0057] The active reactor cavity water injection system comprises a refueling water tank, an A-row active water injection pipeline and a B-row active water injection pipeline arranged in parallel; the refueling water tank is connected to the pressure vessel through the A / B-row active water injection pipelines arranged in parallel.

[0058] Each active water injection pipeline includes an electric valve 1, a check valve 2, a manual valve 3, an electric water pump 4, a normally closed electric valve 5, a No. 2 check valve, and a No. 2 manual valve, which are connected in sequence. The left side of the electric valve 1 is connected to the refueling water tank, and the right side of the No. 2 manual valve is connected to the pressure vessel. The fire water is connected to the No. 3 manual valve and then connected to the active water injection pipeline.

[0059] Fire water is provided between the check valve 2 and the manual valve 3 of each active water injection pipeline.

[0060] The active reactor cavity water injection system also includes a water injection pump, an AC / DC power supply, and an equipment cooling system.

[0061] Each of the A column active water injection pipeline and the B column active water injection pipeline is equipped with a 380V emergency AC power supply, a 110V DC power supply, a 48V DC power supply, and a 6.6kV emergency AC power supply.

[0062] In step 3), the initial value of pipeline equipment is set to 0. When the accident site reports that the pipeline is damaged and lost its function, the status parameter of the pipeline equipment is set to 1; the initial value of the manual valve and check valve is 0, and the status parameter is set to 1 when the equipment is unavailable; the availability of the water tank is determined by the water tank level. When the liquid level is higher than 2.1m, the equipment status is 0; when the liquid level is less than 2.1m, the equipment status is 1, which is considered unavailable. The status parameters of each device are Fig. 9As shown. The judgment standard for the availability of 380V emergency AC power supply in A / B column is voltage ≥ 342V. The judgment standard for the availability of 110V DC power supply in A / B column is voltage > 102.3V. The judgment standard for the availability of 48V DC power supply in A / B column is voltage > 30V. The judgment standard for the availability of 6.6kV emergency AC power supply in A / B column is voltage > 0.8Un. The judgment standard for the availability of electric pump cooling water is that the cooling water flow rate of the pump motor winding is > 0.8Qn and the winding temperature is ≤ 95℃; the judgment standard for unavailability is that the cooling water flow rate of the pump motor winding is ≤ 0.8Qn or the winding temperature is > 95℃.

[0063] In step 2), the fault tree of the active reactor cavity water injection system includes three layers of basic events: the first layer of basic events includes water injection valve failure, refueling water tank water intake failure, and fire water tank water intake failure; the above three basic events are in a logical or relationship.

[0064] The second-level basic events corresponding to the failure of the water injection valve include the failure of the manual valve and the failure of the check valve, which are logically related to each other.

[0065] The second-level basic events corresponding to the failure of water extraction from the refueling water tank include the failure of water extraction from the refueling water tank in column A and the failure of water extraction from the refueling water tank in column B, which are in a logical AND relationship with each other.

[0066] The third-level basic events corresponding to the failure of water intake from the refueling water tank of column A include three basic events with a logical OR relationship with each other: failure of water intake from the refueling water tank of column A, failure of the electric water intake pump of column A, and failure of the pipeline behind the pump of column A; each of the above three basic events is provided with a transfer gate.

[0067] The third-level basic events corresponding to the failure of water intake from the B-train refueling water tank include three basic events with a logical OR relationship between each other: failure of water intake from the B-train refueling water tank, failure of the B-train electric water intake pump, and failure of the pipeline behind the B-train pump; each of the above three basic events is provided with a transfer gate.

[0068] The second-level basic events corresponding to the failure of fire water tank water intake include the failure of fire water tank water intake in column A and the failure of fire water tank water intake in column B, which are logically ANDed to each other. The third-level basic events corresponding to the failure of fire water tank water intake in column A include three basic events with logical OR relationship: failure of fire water tank water intake in column A, failure of electric water intake pump in column A, and failure of pipeline behind pump in column A; each of the above three basic events is provided with a transfer gate. The third-level basic events corresponding to the failure of fire water tank water intake in column B include three basic events with logical OR relationship: failure of fire water tank water intake in column B, failure of electric water intake pump in column B, and failure of pipeline behind pump in column B; each of the above three basic events is provided with a transfer gate.

[0069] The fault tree of the failure of the water intake pipeline of the refueling water tank of column A or column B includes four basic events. The first basic event includes the failure of the refueling water tank, the failure of the electric valve, and the failure of the water intake pipeline, which are logically related to each other.

[0070] The second-level basic events corresponding to the failure of the refueling water tank include the refueling water tank filter blockage and the refueling water tank water level low, which are in a logical AND relationship with each other.

[0071] The second-level basic events corresponding to the failure of the water intake pipeline include manual valve failure, check valve failure, electric valve failure, and pipeline failure, which are logically related to each other.

[0072] The third-level basic events corresponding to the electric valve failure include the electric valve power failure and the electric valve body failure, which are logically ORed to each other. The third-level basic events corresponding to the electric valve power failure include the 380V AC power failure, the 110V DC power failure, and the 48V DC power failure, which are logically ORed to each other.

[0073] The A / B water intake pump failure fault tree includes two levels of basic events. The first level of basic events includes pump body failure, pump power loss, and pump cooling water loss, which are logically related to each other.

[0074] The second-level basic events corresponding to the loss of pump power include the loss of 6.6kV emergency AC power supply and the loss of 110V DC power supply, which are logically OR-related to each other.

[0075] The fault tree for failure of the water intake pipeline after the A or B column pump includes four basic events. The first basic event includes failure of the pipeline valve inside the containment, failure of the pipeline, and failure of the pipeline valve outside the containment, which are logically ORed. The second basic event corresponding to the failure of the pipeline valve inside the containment includes failure of the check valve and failure of the manual valve, which are logically ANDed. The second basic event corresponding to the failure of the pipeline valve outside the containment includes failure of the manual valve, failure of the electric valve of the A / B column, and failure of the check valve, which are logically ORed. The third basic event corresponding to the failure of the electric valve of the A / B column includes failure of the electric valve power supply and failure of the electric valve body, which are logically ORed. The fourth basic event corresponding to the failure of the electric valve power supply includes loss of 380V AC power supply, loss of 110V DC power supply, and loss of 48V DC power supply, which are logically ORed.

[0076] The fault tree of fire water intake pipeline failure in column A or B includes three layers of basic events. The first layer of basic events includes manual valve failure, pipeline failure, and fire water production / distribution system pipeline failure, which are logically ORed to each other. The second layer of basic events corresponding to the fire water production / distribution system pipeline failure include manual valve failure of nuclear island fire water production system and manual valve failure of nuclear island fire water distribution system, which are logically ORed to each other. Manual valve failure of nuclear island fire water production system includes manual valve 1 failure and manual valve No. 3 failure, which are logically ANDed to each other.

[0077] The availability evaluation method of the active reactor cavity water injection system combined with the passive one provided by the present invention can also be used to evaluate the availability of the passive reactor cavity water injection system.

Claims

1. A method for evaluating the availability of an active reactor cavity water injection system combined with a passive one, characterized in that: The following steps are involved: 1) Draw a simplified flow chart of the reactor cavity water injection cooling system; 2) Construct the system availability fault tree logic diagram: Use AND gates, OR gates, and transfer gates to construct the system failure fault tree logic diagram according to the simplified flow chart of the reactor cavity water injection cooling system in step 1). The status of the terminal equipment is used as the basic event of the fault tree: 3) Obtaining equipment status parameters: Obtain the status parameters of each device in the reactor cavity water injection cooling system through the nuclear power plant information system and data interface. The available equipment is represented by 0, and the unavailable equipment is represented by 1; 4) Availability evaluation: By performing logical calculations on the fault tree, when the result is 0, the active cavity water injection cooling system is available; when the result is 1, the active cavity water injection cooling system is unavailable.

2. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive one as claimed in claim 1, characterized in that: In the step 1), the reactor cavity water injection cooling system comprises an active reactor cavity water injection system and a passive reactor cavity water injection system arranged in parallel; the passive reactor cavity water injection system comprises a reactor cavity water injection cooling water tank and two passive water injection pipelines; the reactor cavity water injection cooling water tank is connected to the pressure vessel via the two passive water injection pipelines arranged in parallel; the cooling water in the reactor cavity water injection cooling water tank is passively injected into the reactor cavity by gravity.

3. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive one as claimed in claim 2, characterized in that: In the step 1), the active reactor cavity water injection system comprises a refueling water tank, an A column active water injection pipeline and a B column active water injection pipeline arranged in parallel; the refueling water tank is connected to the pressure vessel via the A / B column active water injection pipelines arranged in parallel; each active water injection pipeline comprises an electric valve (1), a check valve (2), a manual valve (3), an electric water pump (4), a normally closed electric valve (5), a No. 2 check valve, and a No. 2 manual valve connected in sequence, wherein the left side of the electric valve (1) is connected to the refueling water tank, and the right side of the No. 2 manual valve is connected to the pressure vessel; fire water is arranged between the check valve (2) and the manual valve (3) of each active water injection pipeline; and the fire water is connected to the No. 3 manual valve and then connected to the active water injection pipeline.

4. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive one as claimed in claim 3, characterized in that: In the step 3), the initial value of the pipeline equipment is set to 0, and when the equipment is unavailable, the state parameter is set to 1; the initial value of the manual valve and the check valve is 0, and when the equipment is unavailable, the state parameter is set to 1; the availability of the water tank is determined by the water tank liquid level, when the liquid level is higher than 2.1m, the equipment state is 0; when the liquid level is less than 2.1m, the equipment state is 1.

5. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive one as claimed in claim 4, characterized in that: In the step 2), the fault tree of the active reactor cavity water injection system includes three layers of basic events: the first layer of basic events includes water injection valve failure, refueling water tank water intake failure, and fire water tank water intake failure, and the above three basic events are in a logical OR relationship; the second layer of basic events corresponding to the water injection valve failure include manual valve failure and check valve failure, which are in a logical OR relationship with each other; the second layer of basic events corresponding to the refueling water tank intake failure include A column refueling water tank intake failure and B column refueling water tank intake failure, which are in a logical AND relationship with each other; the third layer of basic events corresponding to the A column refueling water tank intake failure include three basic events in a logical OR relationship with each other: A column refueling water tank intake failure, A column electric water intake pump failure, and A column pump rear pipeline failure, and the above three basic events are all provided with a transfer gate; the third layer of basic events corresponding to the B column refueling water tank intake failure include The third layer of basic events corresponding to the failure of water intake from the fire water tank in the column A include three basic events with a logical OR relationship: failure of water intake from the refueling water tank in the column B, failure of the electric water intake pump in the column B, and failure of the pipeline behind the pump in the column A. A transfer gate is set for each of the three basic events; the third layer of basic events corresponding to the failure of water intake from the fire water tank in the column A include three basic events with a logical OR relationship: failure of water intake from the fire water tank in the column A, failure of the electric water intake pump in the column A, and failure of the pipeline behind the pump in the column A. A transfer gate is set for each of the three basic events; the third layer of basic events corresponding to the failure of water intake from the fire water tank in the column B include three basic events with a logical OR relationship: failure of water intake from the fire water tank in the column B, failure of the electric water intake pump in the column B, and failure of the pipeline behind the pump in the column B. A transfer gate is set for each of the three basic events.

6. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive one as claimed in claim 5, characterized in that: The fault tree of the failure of the water intake pipeline of the refueling water tank in column A or column B in the step 2) includes four layers of basic events; the first layer of basic events includes failure of the refueling water tank, failure of the electric valve, and failure of the water intake pipeline, which are logically related to each other; the second layer of basic events corresponding to the failure of the refueling water tank includes blockage of the refueling water tank filter and low water level in the refueling water tank, which are logically related to each other; the second layer of basic events corresponding to the failure of the water intake pipeline includes failure of the manual valve, failure of the check valve, failure of the electric valve, and failure of the pipeline, which are logically related to each other; the third layer of basic events corresponding to the failure of the electric valve includes failure of the electric valve power supply and failure of the electric valve body, which are logically related to each other; the third layer of basic events corresponding to the failure of the electric valve power supply includes power failure of 380V AC power supply, power failure of 110V DC power supply, and power failure of 48V DC power supply, which are logically related to each other.

7. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive one as claimed in claim 6, characterized in that: The A / B water intake pump failure fault tree in step 2) includes two layers of basic events; the first layer of basic events includes pump body failure, pump power loss, and pump cooling water loss, which are logically OR-related to each other; the second layer of basic events corresponding to the pump power loss include 6.6kV emergency AC power loss and 110V DC power loss, which are logically OR-related to each other.

8. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive one as claimed in claim 7, characterized in that: The fault tree of the failure of the water intake pipeline after the A or B column pump in the step 2) includes four layers of basic events; the first layer of basic events includes failure of the pipeline valve inside the containment, pipeline failure, and failure of the pipeline valve outside the containment, which are logically ORed to each other; the second layer of basic events corresponding to the failure of the pipeline valve inside the containment includes failure of the check valve and failure of the manual valve, which are logically ANDed to each other; the second layer of basic events corresponding to the failure of the pipeline valve outside the containment includes failure of the manual valve, failure of the electric valve of the A / B column, and failure of the check valve, which are logically ORed to each other; the third layer of basic events corresponding to the failure of the electric valve of the A / B column includes failure of the electric valve power supply and failure of the electric valve body, which are logically ORed to each other; the fourth layer of basic events corresponding to the failure of the electric valve power supply includes power failure of 380V AC power supply, power failure of 110V DC power supply, and power failure of 48V DC power supply, which are logically ORed to each other.

9. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive system as claimed in claim 8, characterized in that: The fire water intake pipeline failure fault tree of column A or B in step 2) includes three layers of basic events; the first layer of basic events includes manual valve failure, pipeline failure, and fire water production / distribution system pipeline failure, which are logically ORed to each other; the second layer of basic events corresponding to the fire water production / distribution system pipeline failure include nuclear island fire water production system manual valve failure and nuclear island fire water distribution system manual valve failure, which are logically ORed to each other; the nuclear island fire water production system manual valve failure includes manual valve (3) failure and No. 3 manual valve failure, which are logically ANDed to each other.

10. The method for evaluating the availability of an active reactor cavity water injection system combined with a passive system according to any one of claims 1 to 9, characterized in that: The availability evaluation method of the active reactor cavity water injection system combined with the passive one can also be used to evaluate the availability of the passive reactor cavity water injection system.

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