JPH05281388A - Automatic depressurization system for boiling water reactor power plant - Google Patents

Abstract

PURPOSE:To depressurize with a variety of redundant water injection systems having improved safety by providing a set point of low and high reactor pressure and a judgement means indicating the operation of the water injection system driven by turbine. CONSTITUTION:The title system has a turbine driven water injection system and a low pressure water injection system. The operating reactor pressure is set above the isolation set pressure of the turbine driven steam pipe and the low reactor pressure signal 4 is set below the water injection initiation pressure for the low pressure injection system. And the set point of high reactor pressure signal 3 is below the injection initiation pressure for the low pressure injection system and over the set point of low reactor pressure signal 4. Also a judgment means generating operating signal 2 of the turbine driven water injection system is provided. When the automatic depressurization system automatically actuates to open the automatic depressurization valve, an automatic depressurization valve openned at the set point of the signal 4 is closed during the generation of the signal 2. When it reaches the set point of the signal 3, the automatic depressurization valve is opened again.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic depressurization system of a boiling water nuclear power plant for continuing water injection to a nuclear reactor in a turbine driven water injection system.

[0002]

2. Description of the Related Art A boiling water nuclear power plant is provided with a plurality of emergency water injection systems for injecting water into the reactor and cooling the core in the event of an accident or a transient change. Generally, these water injection systems include a low pressure water injection system and a turbine-driven high pressure water injection system in order to provide diversity.

An outline of a conventional turbine-driven water injection system will be described with reference to FIG. In FIG. 4, the reactor 40 is housed in a reactor containment vessel 41, and an isolation valve 31 is installed in a steam pipe 30 for driving the turbine from the reactor 40 to the turbine 32.
a and 31b are provided to separate the wall surface of the reactor containment vessel 41. A turbine drive pump 33 is connected to the turbine 32, and a pressure gauge 3 is installed in a water injection line 39 on the discharge side of the pump 33.
4. The minimum flow bypass line 35, the flow meter 36, the test bypass line 37, and the injection valve 38 are sequentially connected.

The turbine-driven water injection system is a system in which water is injected into the reactor 40 by the turbine-driven pump 33. This system drives the turbine 32 with steam generated in the reactor 40,
The drive source for the turbine drive pump 33. Therefore, the turbine 32 cannot be driven when the pressure of the nuclear reactor 40 decreases, so that the turbine drive steam pipe 30 that guides the nuclear reactor steam to the turbine 32 is isolated. Typically,
The reactor pressure for this isolation, that is, the minimum reactor pressure at which the turbine-driven water injection system can be injected is designed to be lower than the reactor pressure at which the low-pressure water injection system described below can be injected. ..

The low-pressure water injection system is a system for injecting water into the reactor 40 when cooling water cannot be supplied to the reactor 40 or the amount of water injection is insufficient due to a high-pressure water injection system including a turbine-driven water injection system, Generally, the amount of water injected is larger than that of the high-pressure water injection system, and a large amount of cooling water can be supplied to the reactor 40. However, since the discharge pressure of the turbine drive pump 33 is low, when the pressure of the reactor 40 is high, it is necessary to operate the automatic depressurization system to reduce the reactor pressure to a pressure at which the low-pressure water injection system can inject water.

In the automatic depressurization system, the shortage of the amount of water injected into the reactor 40 causes the reactor water level to continue to drop, or in addition to this, the high pressure inside the containment vessel 41 indicates the breakage of the piping inside the containment vessel 41. Judgment is based on what is occurring. Further, when the automatic pressure reducing system operates, the automatic pressure reducing valve opens to reduce the pressure of the reactor 40, but at this time, the water held in the reactor 40 becomes steam and flows out from the reactor 40, so low-pressure water injection is performed. In order to ensure water injection into the reactor by the system, it is configured to automatically start after confirming that the low-pressure water injection system is operating normally.

The once-operated automatic depressurization system continues to operate until the operator resets it after the factor causing the automatic start-up is removed, and depressurizes the reactor pressure to almost atmospheric pressure.

[0008]

As described above, the purpose of the automatic depressurization system is to depressurize the reactor and inject water by the low pressure water injection system when the flow rate of water injected into the reactor by the high pressure system is insufficient. However, the automatic depressurization system has the following problems.

That is, even if the turbine-driven water injection system is operating, if the automatic depressurization system operates when the water injection flow rate is insufficient, the reactor is brought to a pressure below the pressure at which the steam pipes of the turbine-driven water injection system are isolated. I will reduce the pressure. Therefore, although the water injection amount is insufficient, the turbine-driven water injection system that continues to inject water into the reactor becomes unusable, reducing the diversity and multiplicity of the water injection system into the reactor. , Reduce safety.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a turbine when an automatic depressurization system is required to operate while the turbine-driven water injection system is operating. Boiling that reduces pressure to improve the safety by ensuring the diversity and redundancy of the water injection system by maintaining the function of the low-pressure water injection system as designed without losing the drive water supply system. It is to provide an automatic decompression system for a water nuclear power plant.

[0011]

[Means for Solving the Problems] A reactor has a turbine-driven water injection system and a low-pressure water injection system, and the reactor pressure is not less than the isolation set pressure of the turbine drive steam pipe and not more than the injection start pressure of the low-pressure water injection system. It has a set point of low pressure, has a set point of reactor pressure high below the injection start pressure of the low pressure injection system and above the set point of low reactor pressure, and the turbine driven water injection system is operating. With means, when the automatic pressure reducing system is automatically activated and the automatic pressure reducing valve is opened, the automatic pressure reducing valve opened at the reactor pressure low set point is closed during operation of the turbine driven water injection system, After that, when the reactor pressure reaches the set point of the reactor pressure high, the automatic pressure reducing valve is configured to be opened again.

[0012]

[Operation] When the discharge pressure of the turbine drive pump is higher than a predetermined set value, or when the system flow rate of the turbine drive water injection system is If it is higher than a predetermined set value, or if the injection valve to the reactor of the water injection system driven by the turbine is open, or if a combination of the three is used.

Therefore, according to the present invention, when the automatic pressure reducing system is required while the turbine-driven water injection system is operating, the reactor pressure does not exceed the pressure for the low-pressure water injection system to function. Although the pressure is reduced, it is not reduced to the pressure at which the turbine-driven water injection system is isolated, ensuring the diversity and redundancy of the water injection system, improving the reliability of the reactor cooling means, and improving the safety of the reactor. It is possible to improve the property.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an automatic depressurization system of a boiling water nuclear power plant according to the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of an automatic depressurization system (hereinafter referred to as ADS) of the present invention. The ADS automatic start signal 1 is the same as that generated by the conventional ADS, and once generated, the cause of the generation is removed, and it is continuously generated unless the operator performs a reset operation. The turbine drive system operating signal 2 is a signal generated when the turbine drive water injection system is operating, and a method of generating this signal will be described later.

The high reactor pressure signal 3 and the low reactor pressure signal 4 are the maximum pourable pressure of the low pressure pouring system shown in FIG. 3 with respect to the reactor pressure, that is, the LPCS pourable point pressure 23, the high reactor pressure signal 3, The low pressure signal 4 and the turbine drive water injection system isolation pressure, that is, the RCIC isolation set point pressure 22 are set to decrease in this order. This setting method will be described later.

When the ADS automatic start signal 1 is generated,
When the turbine drive water injection system is not operating, the turbine drive system operating signal 2 is not generated, so NOT logic 6 is established, AND logic 5 and OR logic 11 are established, and the automatic pressure reducing valve (hereinafter ADS) is established. An open signal 13 (referred to as a valve) is generated, and the reactor is depressurized to a pressure below the pressure at which the low pressure water injection system can inject water, and this depressurized state is maintained. In this case, the conventional AD
Performs exactly the same operation as S.

When the turbine driven water injection system is operating, the turbine drive system operating signal 2 is generated.
AND logic 5 does not hold. At the initial stage of generation of the ADS automatic start signal 1, the reactor pressure is high, so that the reactor pressure high signal 3 is generated. Therefore, the AND logic 10 is established, the OR logic 11 is established, and the ADS valve open signal 13 is generated. This opens the ADS valve and depressurizes the reactor.

Once this ADS valve open signal 13 is generated,
Even if the reactor pressure high signal 3 does not hold, while the reactor pressure low signal 4 does not hold, NOT logic 7 and AN
Since D logic 10 is established, it is held by AND logic 8 and OR logic 9, AND logic 10 and OR logic 11 continue to be established, ADS valve open signal 13 continues to be established, and the ADS valve remains open. Then, the pressure reduction is continued, and the pressure is reduced to a pressure lower than the water injection pressure of the low pressure water injection system.

When the reactor pressure reduction progresses and the reactor pressure low signal 4 is satisfied, the NOT logic 7 is not satisfied, the AND logic 8 is not satisfied, and the reactor pressure high signal 3 is also satisfied. Since it disappears, OR logic 9, AND logic 10,
OR logic 11 is no longer valid. Therefore, NOT logic
12 is satisfied, the ADS valve closing signal 14 is generated, the ADS valve is closed, and the depressurization of the reactor is stopped, but at this point, the reactor pressure low signal 4 exceeds the isolation set pressure of the turbine driven water injection system. Since it is set, the turbine-driven water injection system can continue to inject water into the reactor.

When the ADS valve is closed, the decay pressure in the reactor causes the reactor pressure to gradually rise. When the reactor pressure rises until the high reactor pressure signal 3 is established, the ADS valve opening signal 13 is generated again by the same process as described above, and the reactor is depressurized until the low reactor pressure signal 4 is established again. It

As described above, according to the present invention, once the ADS automatic start signal 1 is established, the reactor pressure is maintained between the set point of the high reactor pressure signal 3 and the set point of the low reactor pressure signal 4. During this period, it is possible to continue injecting water into the reactor through both the low-pressure injection system and the turbine-driven injection system.

Next, a method of generating the in-operation signal 2 of the turbine-driven water injection system will be described. The turbine-driven water injection system has a schematic configuration as shown in FIG. The turbine 32 is configured to guide and drive the steam generated in the nuclear reactor 40 by the steam pipe 30 for driving the turbine. The steam pipe 30 is provided with isolation valves 31a and 31b inside and outside the containment vessel 41, and when the pressure in the reactor 40 becomes equal to or lower than the isolation set point pressure 22, these isolation valves 31a and 31b are closed to supply steam. Becomes impossible.

When the turbine-driven water injection system is operating, the injection valve 38 is opened, and the pump 33 driven by the turbine 32 causes water from a water source (not shown) to the reactor 40 via the water injection pipe 39. It is configured to inject water. Since the discharge pressure of the pump is established during operation of the turbine-driven water injection system, the pressure gauge 34 installed at the pump outlet shows a state higher than the standby pressure. Also the flow meter of the system
The amount of water injected into 36 reactors is shown. Therefore, when there is no abnormality in the turbine-driven water injection system and water is being injected into the reactor 40, the discharge pressure gauge 34 of the turbine-driven pump is higher than a predetermined set value, or the turbine-driven water injection system system. This can be detected by detecting either the case where the flow meter 36 is higher than a predetermined set value, or the case where the injection valve 38 to the reactor of the turbine driven water injection system is opened.

However, these respective signals do not always occur only when the turbine-driven water injection system is injecting water into the reactor 40. That is, the injection valve 38
Will also be opened in regular tests. Further, the discharge pressure gauge 34 is established even when the injection valve 38 is not opened and water is flowing only through the minimum flow rate bypass line 35 provided to avoid the shutoff operation of the pump 33. Further, the discharge pressure gauge 34 is established even during the flow rate test using the test bypass line 37 provided to test whether the pump can satisfy the predetermined flow rate, and the system flow meter 36 shows the predetermined flow rate.

Therefore, in order to reliably judge whether or not the turbine-driven water injection system is operating, it is desirable to appropriately combine the three signals. FIG. 2 is an example of the configuration, and is configured to determine that the turbine-driven water injection system is operating when all of the signals are satisfied.

With this configuration, when the turbine-driven water injection system is determined to be operating, it is operating reliably, but when no signal is generated, the turbine actually operating is in operation. It is possible to determine that the drive water injection system is not in operation. In such a case, if two or more of the three signals are satisfied, it may be determined that the turbine-driven water injection system is operating.

How to determine the combination of these three signals depends on how reliable the turbine driven water injection system is to design the operating signal in consideration of malfunction or non-operation. Entrusted to the design of.

Next, a method of setting the high reactor pressure signal 3 and the low reactor pressure signal 4 will be described. As an example, FIG. 3 shows an outline of the RCIC characteristic curve 20 as a reactor pressure and turbine driven water injection system of a boiling water reactor and the LPCS characteristic curve 21 as a low pressure water injection system. RC
The IC is designed to inject the rated flow up to a reactor pressure of approximately 10 kg / cm ² g, the RCIC isolation set point pressure 22 of the steam pipe 30 is set to approximately 3.5 kg / cm ² g and below this will work. It is designed to disappear. On the other hand, the LPCS allows injection of water into the reactor, and the LPCS injection point pressure 23
Is about 20 kg / cm ² g, and is designed so that the rated flow rate can be injected at about 8 kg / cm ² g.

In the embodiment shown in FIG. 3, the set point of the reactor pressure low signal 4 which is above the RCIC isolation set point pressure 22 of the RCIC steam pipe and below the LPCS water injection possible point pressure 23 is about 8 kg / cm ² g. Set to LPCS water injection point pressure 23
The set point of the reactor pressure high signal 3 which is less than or equal to the set point of the reactor pressure low signal 4 is set to about 14 kg / cm ² g.

By setting the set points of the high reactor pressure signal 3 and the low reactor pressure signal 4 in this manner, the ADS
Even after the operation of the reactor, the reactor pressure was about 8 kg / cm ² g and about 14 kg.
/ Cm ² g is maintained between, LPCS, RCIC together it is possible to injection flow rate of approximately 70% of the rated flow rate to the reactor.

In this case, it is not always possible to inject water into the reactor at the rated flow rate in both systems.
The PCS is designed with the required flow rate for the event that the reactor is decompressed so that the rated flow can be injected even if the ADS does not operate. Can cool the reactor sufficiently with a water injection volume less than the rated flow rate and maintain safety. Further, regarding RCIC, it contributes to the cooling of the nuclear reactor to a greater extent than when the water injection amount becomes zero, and it is possible to improve safety.

In the case of this embodiment, the set points of the high reactor pressure signal 3 and the low reactor pressure signal 4 are about 8 kg /
cm ² g and about 14 kg / cm ² g were set, but in general, these set points are the required amount of water injection of the low pressure water injection system and its injection characteristics, and the amount of water injection of the turbine driven water injection system and its isolation. Based on the set pressure, LPCS water injection possible point pressure 23, high reactor pressure signal 3, low reactor pressure signal 4, RCIC isolation set point pressure 22 for turbine drive water injection system You can get the effect
The diversity and multiplicity of the water injection system will increase more than before, and it will be possible to further improve the safety of the reactor.

Further, since it is sufficient to modify the existing plant only by adding the logic as shown in FIGS. 1 and 2, it is possible to improve the safety at low cost.

The above-described one embodiment of the present invention has been described for the case where the turbine driven water injection system and the low pressure water injection system of the boiling water reactor are each one system, but different characteristics (water injection amount with respect to the reactor pressure are described. , Rated injection volume, isolated set pressure) for reactors with multiple turbine-driven injection systems or low-pressure injection systems installed, the reactor pressure high and low set points and operating signals described above. Is set in multiple stages according to each water injection system and its combination, and by forming the logic described above for each,
The available water injection system may be maximized.

[0035]

According to the present invention, since the automatic pressure reducing system operates the turbine-driven water injection system that was normally operating before the automatic pressure reducing system operates, the original function of the turbine drive water injection system is not lost. It is possible to inject water into the reactor of the low-pressure water injection system, which is the purpose of. For this reason, the diversity and multiplicity of the water injection system will increase more than before, and it will be possible to further improve the safety of the nuclear reactor. Moreover, since the present invention can be applied to an existing plant only by modifying the existing logic, safety can be improved at low cost.

[Brief description of drawings]

FIG. 1 is a logic diagram for controlling opening / closing of an automatic pressure reducing valve in an embodiment of an automatic pressure reducing system of a boiling water nuclear power plant according to the present invention.

FIG. 2 is a logic diagram for determining that the turbine drive in FIG. 1 is operating.

FIG. 3 is a characteristic diagram showing a relationship between set points of high and low reactor pressures and water injection characteristics of a turbine driven water injection system and a low pressure driven water injection system in the present invention.

FIG. 4 is a schematic configuration diagram of a turbine-driven water injection system.

[Explanation of symbols]

1 ... ADS automatic start signal, 2 ... in-operation signal, 3 ... reactor pressure high signal, 4 ... reactor pressure low signal, 5,8,10,18 ...
AND logic, 6, 7, 12 ... NOT logic, 9, 11 ... OR logic, 13 ... ADS valve open signal, 14 ... ADS valve close signal, 15 ... Pump discharge pressure establishment signal, 16 ... High system flow rate signal, 17 ... Injection valve open signal, 20 ... RCIC characteristic curve, 21 ... LPCS characteristic curve, 22 ... RCIC isolation set point pressure, 23 ... LPCS water injection point pressure, 30 ... Steam pipe, 31a, 31b ... Isolation valve, 32 ... Turbine , 33 ... Turbine driven pump, 34 ... Pressure gauge, 35 ... Minimum flow bypass line, 36 ... Flow meter, 37 ... Test bypass line, 38 ... Injection valve, 39 ... Injection line, 40 ... Reactor,
41 ... Storage container.

Claims (1)

[Claims] 1. A low pressure reactor system having a turbine-driven water injection system and a low-pressure water injection system, in which the reactor pressure is higher than the isolation set pressure of the turbine drive steam pipe and lower than the water injection start pressure of the low-pressure water injection system. With a point, having a low pressure injection system water injection starting pressure and a reactor pressure high set point above the reactor pressure low set point and having a determination means that the turbine driven water injection system is operating, When the automatic pressure reducing system is automatically started and the automatic pressure reducing valve is opened, the automatic pressure reducing valve opened at the reactor pressure low set point is closed while the turbine-driven water injection system is operating, and then the reactor pressure is reduced. Is configured to reopen the automatic pressure reducing valve when the reactor pressure high set point is reached, the automatic pressure reducing system for a boiling water nuclear power plant.