JPH0943381A - Operation method of residual heat removal system of nuclear reactor - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent human error, ensure the containment vessel is cooled, and improve the safety of the reactor. [Structure] The pump 4 that takes water from the suppression pool 1 due to a loss of coolant accident is started, the test bypass valve 12 on the suppression pool return line 11 is closed, and the bypass valve 7 on the heat exchanger bypass line 6 is closed.
Further, the injection valve 10 on the reactor water injection line 9 is opened, and the bypass valve 7 is automatically closed after a predetermined time elapses in this state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating a residual heat removal system of a nuclear reactor, and more particularly to an operation method of a residual heat removal system for efficiently removing heat from a containment vessel of a boiling water reactor.

[0002]

2. Description of the Related Art The residual heat removal system of a boiling water reactor works together with other emergency core cooling systems in the event of a coolant loss accident to prevent damage to the fuel cladding by recovering and maintaining the reactor water level. It is also installed for the purpose of transferring the heat inside the containment vessel of the reactor to the outside of the containment vessel.

A conventional method of operating the residual heat removal system will be described below with reference to FIG.

As shown in the schematic configuration of FIG. 6, the residual heat removal system of a boiling water reactor is generally a suppression pool 1
A suction line 3 for taking out the suppression pool water 2 from the suction line 3, a residual heat removal pump 4, a heat exchanger 5, a line 6 bypassing the heat exchanger 5, and an isolation valve 7 on the line 6.
(Hereinafter referred to as a heat exchange bypass valve), a line 9 for injecting water into the reactor 8 and an isolation valve 10 (hereinafter referred to as an injection valve) on the line 9, a return line 11 to the suppression pool 1, and an isolation on the line 11. A valve 12 (hereinafter referred to as a test bypass valve) is provided. The suction line 3 and the residual heat removal pump 4 connected to the suppression pool 1 may be multiplexed to improve reliability. Reference numeral 13 is a dry well, 14 is a vent pipe connecting the dry well 13 and the suppression pool 1, and 15 is a relief safety valve. Further, the residual heat removal system shown in FIG. 6 is in a standby state, the heat exchange bypass valve 7 is open, and the injection valve 10 and the test bypass valve 12 are closed.

In this way, the residual heat removal system has a low-pressure water injection function of injecting the water 2 of the suppression pool 1 into the reactor 8 in the event of loss of the coolant, and cooling the suppression pool water 2 with the heat exchanger 5. Suppression pool 1 again
It is a system that has a versatile function of cooling the suppression pool.

The low pressure water injection function is automatically activated when a loss of coolant accident occurs. FIG. 7 shows the logic of this automatic start-up, when the pressure in the drywell 13 is equal to or higher than the preset pressure high set point and the D / W pressure high signal 20 is generated, or when the reactor water level is preset. When a reactor water level low signal 21 occurs below the set reactor water level low set point (referred to as L-1), it is determined that a coolant loss accident has occurred, and a coolant loss accident signal 22 is established. To do. Once the coolant loss accident signal 22 is satisfied, it is held until the reset operation is performed. In response to the establishment of the loss-of-coolant signal 22, the residual heat removal pump start signal 2
3, the injection valve opening signal 24, the heat exchange bypass valve opening signal 25, and the test bypass valve closing signal 26 are output respectively, and the suppression pool water 2 is designed to be automatically injected into the reactor 8.

The capacity of the residual heat removal pump 4 is designed so that a predetermined amount can be injected into the reactor 8 in the event of a loss of coolant accident when the heat exchange bypass valve 7 is open.

It is a routine test that the open signal is output to the heat exchange bypass valve 7 in the open state and the close signal is output to the test bypass valve 12 in the closed state during the standby due to the occurrence of the loss of coolant. Even if the valve is not in standby,
This is because it is possible to automatically shift to a state in which a loss of coolant accident occurs.

On the other hand, the suppression pool cooling function is
When the temperature of the suppression pool water 2 rises,
The residual heat removal pump 4 is started, the test bypass valve 12 is opened, and the heat exchange bypass valve 7 is closed by manual operation, and operation is performed via the heat exchanger 5 so that a cooling effect is produced.

Further, it is necessary to cool the containment vessel in the event of a loss of coolant. In the event of a loss of coolant, the cooling water injected into the reactor 8 flows into the dry well 13 from the breakage port, and circulates to the suppression pool 1 via the vent pipe 14 that connects the dry well 13 and the suppression pool 1. Therefore, heat removal from the containment vessel is achieved by cooling the circulating cooling water with the heat exchanger 5,
If necessary, the heat exchange bypass valve 7 on the line 6 that bypasses the heat exchanger 5 is manually closed.

[0011]

After the accident of loss of coolant or when the temperature of the suppression pool water 2 becomes high, it is necessary to cool the containment vessels. However, as mentioned above, these containment vessels are cooled. The operation of the residual heat removal system to do so had to be manually started.

Further, the valves (heat exchange bypass valve 7, injection valve 10, test bypass valve 12) that need to be operated at this time are all designed to allow fine adjustment of the opening for other purposes. Therefore, to move these valves from the fully open state to the fully closed state or from the fully closed state to the fully open state, it is necessary to keep holding the operation switch, and operate the residual heat removal system to cool the containment vessel. To do so, it took a considerable amount of time to operate the switches.

Further, since the cooling of the containment vessel is less urgent than the injection of the coolant into the nuclear reactor, even if the cooling operation of the containment vessel is started, in the case of a loss of coolant, etc. Frequent emergency operations often interrupted the containment vessel cooling operation.

When another urgent operation is interrupted during the operation of the residual heat removal system in the containment vessel cooling mode, the operator is less likely to concentrate on the other operation. However, there is a possibility of human error such as forgetting that the operation to put the residual heat removal system into the containment vessel cooling mode was being performed, and the reliability of the containment vessel cooling operation may be uncertain. It was

Moreover, such a situation is highly likely to occur when the containment vessel cooling operation needs to be carried out more reliably, such as after a loss of coolant, and is a factor that reduces the safety of the entire reactor. Conceivable.

As an improvement plan for solving these problems, a residual heat removing system disclosed in, for example, Japanese Patent Laid-Open No. 17598/1993 is known. However, in this residual heat removal system, it is conceivable that the reactor water level will not shift to the containment vessel cooling mode in the event of a large loss of coolant loss accident that does not recover to L-1. If the other emergency core cooling system does not operate and the residual heat removal system independently secures the reactor water level, the containment vessel cooling mode is set when the reactor water level is restored to L-1. , It became impossible to secure the reactor water level, the reactor water level became L-1 or less again, the low pressure injection mode was entered, and the reactor water level was restored to L-1 again, the containment vessel again. There is a possibility of repeating the cycle of shifting to the cooling mode.

The present invention has been made in view of the above circumstances. By automating the cooling operation of the containment vessel, human error caused by interruption of the cooling operation of the containment vessel due to another operation can be prevented, and the containment vessel Ensure cooling,
An object of the present invention is to provide a method for operating a residual heat removal system that improves the safety of a nuclear reactor.

[0018]

In order to achieve the above object, the present invention comprises a pump for taking water from a suppression pool, a heat exchanger for cooling the taken suppression pool water, and a heat exchange with a bypass valve. The heat exchanger bypass line that bypasses the reactor, the reactor water injection line that injects the suppression pool water that has passed through the heat exchanger or the heat exchanger bypass line into the reactor through the injection valve, and the branch upstream of the injection valve. In the operation method of the residual heat removal system having a heat exchanger via the test bypass valve or the suppression pool water that has passed through the heat exchanger bypass line and returning the suppression pool water to the suppression pool, the suppression pool returns due to a loss of coolant accident. Close the test bypass valve on the line and bypass the heat exchanger bypass line. It is characterized by opening the injection valve and the injection valve on the reactor water injection line, driving the pump, and automatically closing the bypass valve on the heat exchanger bypass line after a lapse of a predetermined time. .

In this operating method, the predetermined fixed time is at least the time required to recover to the predetermined reactor water level after the coolant loss accident occurs.

The predetermined reactor water level is
It should be above the minimum reactor water level required to prevent core damage.

Further, according to the present invention, a pump for taking water from the suppression pool, a heat exchanger for cooling the taken-in suppression pool water, a heat exchanger bypass line having a bypass valve for bypassing the heat exchanger, and a heat exchange Reactor water injection line that injects suppression pool water that has passed through the reactor or heat exchanger bypass line into the reactor through the injection valve, and a heat exchanger or heat exchanger that branches off on the upstream side of the injection valve and through the test bypass valve In the operation method of the residual heat removal system that has a suppression pool return line that returns the suppression pool water that has passed through the bypass line to the suppression pool, the test bypass valve on the suppression pool return line was closed due to the loss of coolant accident, and the heat exchanger bypass By-pass valve on line and injection valve on reactor water injection line When the pump is opened, the pump is driven, and when the reactor water level recovers above the predetermined reactor water level after the elapse of a predetermined time, the bypass valve on the heat exchanger bypass line is automatically closed. It is characterized by

Further, according to the present invention, in the above operating method, after the bypass valve bypassing the heat exchanger is automatically closed, the loss of coolant accident is not a major breakage accident, and another emergency core cooling system is used. Is operating, the injection valve on the reactor water injection line is closed and the test bypass valve on the suppression pool return line is opened.

The fact that the coolant loss accident is a major breakage accident is judged by the fact that the reactor water level does not recover to the upper part of the reactor after the elapse of the predetermined time. Alternatively, it is judged by the fact that the reactor water level once fell below the minimum required reactor water level to prevent core damage.

Further, the fact that the other emergency core cooling system is operating means that the pump is driven in the emergency core cooling system, the injection valve is open, the test bypass valve is closed,
Judgment is made when the system flow rate is equal to or higher than a predetermined flow rate.

Further, the present invention is directed to a pump for taking water from the suppression pool, a heat exchanger for cooling the taken-in suppression pool water, a heat exchanger bypass line for bypassing the heat exchanger with a bypass valve, and a heat exchange. Reactor water injection line that injects suppression pool water that has passed through the reactor or heat exchanger bypass line into the reactor through the injection valve, and a heat exchanger or heat exchanger that branches off on the upstream side of the injection valve and through the test bypass valve In the operation method of the residual heat removal system that has the suppression pool return line that returns the suppression pool water that has passed through the bypass line to the suppression pool, the water temperature of the suppression pool is the predetermined temperature when no loss of coolant accident has occurred. Automatically, the pump will automatically start and the heat exchanger bypass Closing operation of the bypass valve on emissions, and is characterized by performing the opening operation of the test bypass valve of the suppression pool return line.

Furthermore, the present invention provides a pump for taking in water from the suppression pool, a heat exchanger for cooling the taken-in suppression pool water, a heat exchanger bypass line provided with a bypass valve for bypassing the heat exchanger, Heat exchanger or heat exchange via a test bypass valve that is branched upstream of the injection valve and the reactor water injection line that injects the suppression pool water that has passed through the exchanger or heat exchanger bypass line into the reactor through the injection valve. In the operation method of the residual heat removal system that has a suppression pool return line that returns the suppression pool water that has passed through the reactor bypass line to the suppression pool, the pressure of the suppression pool is predetermined when no loss of coolant accident has occurred. When it becomes higher than the pressure, the pump will start automatically and the heat exchanger Closing operation of the bypass valve on the line,
And the operation of opening the test bypass valve on the suppression pool return line.

[0027]

In the method for operating the residual heat removal system of the reactor of the present invention, the bypass valve on the heat exchanger bypass line is automatically operated after the low pressure water injection function is operated for a certain time after the occurrence of the loss of coolant accident. Close it. In addition, other than the accident of loss of coolant due to large breakage and during the operation of the emergency core cooling system other than the relevant system, the residual heat removal system is automatically circulated to cool the suppression pool water to cool the containment vessel. Line up.

Even when no coolant loss accident occurs, when the temperature or pressure of the suppression pool becomes high, the suppression pool water is automatically circulated to cool the containment vessel. Lineup of residual heat removal system.

As a result, it is possible to prevent the human error in the operation of cooling the containment vessel and ensure the cooling of the containment vessel, thereby improving the safety of the nuclear reactor.

[0030]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a flow chart showing an embodiment of the operating method of the residual heat removal system of the present invention.

First, referring to FIG. 1, an operation method at the time of a loss of coolant accident will be described. In step 100, as shown in FIG. 7, the coolant loss accident signal 22 is generated by the D / W high pressure signal 20 or the reactor water level low (L-1) signal 21.
Occurs, the pump start signal 23, the injection valve open signal 24, the heat exchange bypass valve open signal 25,
Each signal of the test bypass valve closing signal 26 is generated and each operation is executed. Up to this point, it is the same as the conventional one.

Then, step 102 of the timer is inserted in order to allow a predetermined fixed time to elapse. The delay time of this timer should be set longer than the time required for the reactor to be re-submerged after the loss of coolant accident. This required time is set based on the reactor water level motion during a typical coolant loss accident such as a large break accident shown in FIG. 2 and a small and medium break accident shown in FIG.

Since cooling of the core is ensured by water injection after the elapse of this set time, in order to cool the containment vessel, a heat exchange bypass valve closing signal for closing the heat exchange bypass valve 7 is sent in step 103. appear.

By the way, since these typical reactor water level motions are for a particular accident scenario,
Cooling of the core is ensured even after a certain period of time, but there is a possibility that the core has not been re-submerged. In such a case, in order to give priority to water injection into the reactor, it is determined in step 104 whether the reactor water level is at or above the core upper end (TAF), and it is confirmed that re-submersion is performed at TAF or above.

Here, if the reactor is not re-submerged, it is a large breakage coolant loss accident, and further recovery of the reactor water level cannot be expected, but the heat exchange bypass valve 7 is closed. Accordingly, the cooled coolant is injected into the reactor 8 and circulated from the breakage port to the suppression pool 2 through the vent pipe 14, whereby the containment vessel cooling is secured.

On the other hand, when the nuclear reactor is re-submerged, it is determined in step 105 whether or not another emergency core cooling system maintaining the sub-submersion is operating. This determination is, for example,
As shown in FIG. 4, regarding the emergency core cooling system, the pump is operating 40, the injection valve is opened 41, and the test bypass valve is closed 4.
2. When all the signals of system flow rate 43 are satisfied, it is determined that the system is operating 44.

In the example of FIG. 4, these four signals 40-
Although it is configured to judge that the system is in operation 44 when all of 43 are satisfied at the same time, the determination accuracy is slightly lowered, but it is determined that the system is in operation only when a part of these 4 signals is satisfied. It may be configured to do so.

If it is determined in step 105 that the other emergency core cooling system is operating, the cooling of the core is ensured by the other operating emergency core cooling system, so the containment vessel In order to increase the efficiency of heat removal from the reactor, the water injection line 9 to the nuclear reactor of the residual heat removal system is closed, the return line 11 to the suppression pool is opened, and the suppression pool water 2 is directly cooled. Therefore, in step 106, an injection valve closing signal and a test bypass valve opening signal are generated.

On the other hand, when the other emergency core cooling system is not operating, it is necessary to maintain the injection of water into the reactor, and therefore the suppression pool water 2 cannot be directly cooled. However, even in this case, since the heat exchange bypass valve 7 is in the closed state, the cooled coolant is injected into the reactor 8 and circulated in the suppression pool 1 via the relief safety valve 15, Although a little less efficient, some containment vessel cooling is secured.

Further, when the temperature or pressure of the suppression pool increases in step 107 instead of the loss of coolant accident in step 100, the activation signal of the residual heat removal pump 4 is used to cool the suppression pool water 2. A signal for closing the heat exchange bypass valve 7 and an signal for opening the test bypass valve 12 are generated to promptly start cooling the suppression pool water 2.

FIG. 5 is a flow chart showing another embodiment of the method for operating the residual heat removal system of the present invention. In this example, in order to confirm that the reactor water level has recovered to the reactor water level (L-0) or higher, which is the minimum required to prevent damage to the core,
After setting a timer for the time at which L-0 recovery can be viewed reliably (step 102), a condition for determining whether the reactor water level is L-0 or higher (step 102 ') is inserted.

If the reactor water level is L-0 or higher,
The subsequent operating procedure is similar to that of the embodiment shown in FIG.

On the other hand, in this step 102 ', when the reactor water level is below L-0 which is the minimum required to prevent damage to the core, it is necessary to promptly inject water into the reactor, and hence the subsequent operation is performed. It will be interrupted and will wait further in the low pressure water injection mode until the reactor water level is restored to L-0 or higher.

[0045]

As described above, according to the present invention, the cooling of the containment vessel is automated, the human error caused by the interruption of the cooling operation of the containment vessel due to another operation is prevented, and the containment vessel is cooled. It is possible to improve the safety of the nuclear reactor by operating the residual heat removal system so that the above can be surely performed.

Further, since the part to be improved is limited to a part of the logic circuit relating to the start signal of the pump and the opening / closing signal of the valve, no large-scale mechanical modification is required, and it is inexpensive and easily introduced into the existing plant. It becomes possible to do.

[Brief description of drawings]

FIG. 1 is a flowchart showing a method of operating a residual heat removal system according to an embodiment of the present invention.

FIG. 2 is a graph showing the re-submersion behavior of a nuclear reactor at the time of a major breakage accident.

FIG. 3 is a graph showing the re-submersion behavior of a nuclear reactor at the time of a small-to-medium-sized break accident.

FIG. 4 is a diagram showing a logic for determining the operation of the emergency core cooling system.

FIG. 5 is a flowchart showing a method of operating a residual heat removal system according to another embodiment of the present invention.

FIG. 6 is a block diagram showing a schematic configuration of a residual heat removal system of a boiling water reactor.

FIG. 7 is a diagram showing a conventional automatic operation logic when a loss of coolant accident occurs in a residual heat removal system.

[Explanation of symbols]

 1 ... Suppression pool 3 ... Suction line 4 ... Residual heat removal pump 5 ... Heat exchanger 6 ... Heat exchanger bypass line 7 ... Heat exchange bypass valve 8 ... Reactor 9 Reactor water injection line 10 Injection valve 11 Suppression pool return line 12 Test bypass valve 13 Drywell 14 Vent pipe 15 Relief safety valve

Claims (10)

[Claims] 1. A pump for taking in water from a suppression pool, a heat exchanger for cooling the taken-in suppression pool water, a heat exchanger bypass line having a bypass valve for bypassing the heat exchanger, and the heat exchanger. Or a reactor water injection line for injecting the suppression pool water that has passed through the heat exchanger bypass line into the reactor through an injection valve, and the heat exchanger or the heat exchanger through the test bypass valve that is branched upstream of the injection valve. In a method for operating a residual heat removal system having a suppression pool return line that returns suppression pool water that has passed through a heat exchanger bypass line to the suppression pool, a test bypass valve on the suppression pool return line is closed due to a loss of coolant accident. A bypass valve on said heat exchanger bypass line and said The injection valve on the reactor water injection line is opened, the pump is driven, and after a lapse of a predetermined time, the bypass valve on the heat exchanger bypass line is automatically closed. Operation method of residual heat removal system of furnace. 2. The predetermined time period is set to be at least a time period required for recovering at least a predetermined reactor water level after a coolant loss accident occurs. A method for operating a residual heat removal system of a nuclear reactor described. 3. The method for operating a residual heat removal system of a reactor according to claim 2, wherein the predetermined reactor water level is equal to or higher than a minimum reactor water level required to prevent core damage. . 4. A pump for taking in water from the suppression pool, a heat exchanger for cooling the taken-in suppression pool water, a heat exchanger bypass line for bypassing the heat exchanger, comprising a bypass valve, and the heat exchanger. Or a reactor water injection line for injecting the suppression pool water that has passed through the heat exchanger bypass line into the reactor through an injection valve, and the heat exchanger or the heat exchanger through the test bypass valve that is branched upstream of the injection valve. In a method for operating a residual heat removal system having a suppression pool return line that returns suppression pool water that has passed through a heat exchanger bypass line to the suppression pool, a test bypass valve on the suppression pool return line is closed due to a loss of coolant accident. A bypass valve on said heat exchanger bypass line and said When the injection valve on the reactor water injection line is opened, the pump is driven, and after the elapse of a predetermined time, when the reactor water level is restored to a predetermined reactor water level or higher, the heat exchanger bypass line A method for operating a residual heat removal system of a reactor characterized by automatically closing the upper bypass valve. 5. When the bypass valve that bypasses the heat exchanger is automatically closed and the loss-of-coolant accident is not a major breakage accident, and another emergency core cooling system is operating. 5. The injection valve on the reactor water injection line is closed, and the test bypass valve on the suppression pool return line is opened.
The method for operating the residual heat removal system of a nuclear reactor according to any one of 1. 6. The method according to claim 5, wherein the loss of coolant accident is a major breakage accident is determined by the fact that the reactor water level does not recover to the upper part of the reactor after the elapse of the predetermined fixed time. A method for operating a residual heat removal system of a nuclear reactor described. 7. The coolant loss accident is judged to be a major breakage accident by determining that the reactor water level has once dropped below the minimum reactor water level required to prevent core damage. Item 5. A method for operating a residual heat removal system of a nuclear reactor according to Item 5. 8. A pump is driven in the emergency core cooling system, an injection valve is open, a test bypass valve is closed, and the other emergency core cooling system is operating.
The method for operating a residual heat removal system of a nuclear reactor according to claim 5, wherein the judgment is made based on whether the system flow rate is equal to or higher than a predetermined flow rate. 9. A pump for taking water from the suppression pool, a heat exchanger for cooling the taken suppression pool water, a heat exchanger bypass line having a bypass valve for bypassing the heat exchanger, and the heat exchanger. Or a reactor water injection line for injecting the suppression pool water that has passed through the heat exchanger bypass line into the reactor through an injection valve, and the heat exchanger or the heat exchanger through the test bypass valve that is branched upstream of the injection valve. In a method of operating a residual heat removal system having a suppression pool return line that returns suppression pool water that has passed through a heat exchanger bypass line to the suppression pool, when the loss of coolant accident has not occurred, the water temperature of the suppression pool is When the temperature becomes higher than a predetermined temperature, the pump will automatically start. A method of operating a residual heat removal system of a nuclear reactor, comprising: closing a bypass valve on the heat exchanger bypass line and opening a test bypass valve on the suppression pool return line. 10. A pump for taking water from the suppression pool, a heat exchanger for cooling the taken-in suppression pool water, a heat exchanger bypass line having a bypass valve for bypassing the heat exchanger, and the heat exchanger. Or a reactor water injection line for injecting the suppression pool water that has passed through the heat exchanger bypass line into the reactor through an injection valve, and the heat exchanger or the heat exchanger through the test bypass valve that is branched upstream of the injection valve. In a method of operating a residual heat removal system having a suppression pool return line for returning suppression pool water that has passed through a heat exchanger bypass line to the suppression pool, when the loss of coolant accident has not occurred, the pressure of the suppression pool is When the pressure rises above a predetermined pressure, the pump will automatically start up. Operation, closing the bypass valve on the heat exchanger bypass line, and opening the test bypass valve on the suppression pool return line.