JPH06201880A - Boric acid flowout prevention device - Google Patents

Abstract

PURPOSE:To prevent flowout of boric acid water by terminating the water injection to the core when the activation signal of low pressure emergency core cooling system, the activation signal of boric acid water injection system and the reactor water level high signal are actuated simultaneously. CONSTITUTION:The activation signal 40 of a low pressure core spray system as an activation signal of low pressure core cooling system actuated when the water level in a reactor pressure vessel lowers below a certain level, and the activation signals 41, 42 of low pressure coolant system are input to an OR gate 43. The output signal 44 of this OR gate 43 and the activation signal 45 of boric acid water injection system 45 are input to an AND gate 46. The output signal 47 of the gate 46 and reactor water level high signal 48 which is activated when the water level in the reactor pressure vessel is higher than a main steam line nozzle, are input to the AND circuit 49. If both conditions agree, this circuit 49 outputs a termination signal 50 of low pressure emergency core cooling system. When the temination signal 50 is actuated, the water injection and water level rise are terminated and the boric acid is kept in the core without flowout of coolant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boric acid outflow prevention device related to a boric acid water injection system of a boiling water nuclear power plant.

[0002]

2. Description of the Related Art Generally, a boiling water reactor is constructed as shown in FIG. In FIG. 2, the inside of the reactor containment vessel 1 is divided into a dry well 3 for accommodating the reactor pressure vessel 2 and a pressure suppression chamber 5 for accommodating the pool water 4. Further, a vent pipe 6 is arranged below the dry well 3 and the other end is opened to the pool water 4. A reactor core 7 is housed in the reactor pressure vessel 2. The reactor water whose temperature has been raised in the reactor core 7 evaporates, and the steam and water are separated by a steam separator 9 provided above the shroud head 8, and then the steam is dried by a steam dryer 10. The dried steam is introduced from the main steam pipe 11 to the turbine 14 through the main steam isolation valves 12 and 13. The steam worked in the turbine 14 is condensed by the condenser 15 to become condensed water, and is again injected into the reactor pressure vessel 2 from the water supply pipe 16 via the water supply pump 17. The injected feed water is boosted by the recirculation pump 19 through the recirculation pipe 18, sucks the surrounding feed water through the jet pump 20 arranged in the reactor pressure vessel 2, and moves below the reactor core 7. Be guided. A main steam relief valve is provided on the upstream side of the main steam isolation valve 12 in the main steam pipe 11.
21 is provided, which operates when the pressure in the main steam pipe 11 becomes equal to or higher than a predetermined value, and the steam in the main steam pipe 11 is released from the pressure suppression chamber 5 via the main steam release pipe 22. It is designed to lead into pool water 4. Further, when the water level in the reactor pressure vessel 2 falls below a predetermined value from the pressure suppression chamber 5 via the low pressure core spray pump 23 and the high pressure core spray pump 24, the pool water 4 is guided above the core 7. A low-pressure core spray pipe 25 and a high-pressure core spray pipe 26 are arranged like a crank. Then, a low-pressure water injection pipe 30 for injecting water from the pressure suppression chamber 5 into the core 7 via a low-pressure water injection pump 29.
Is provided. Further, a boric acid water injection tank 28 is arranged in the reactor pressure vessel 2 via a boric acid water injection pipe 27.

In the normal operation state of the boiling water reactor having the above-mentioned structure, the steam generated in the core 7 is generated by rotating the turbine 14 through the main steam pipe 11. At this time, if a transient change occurs that shuts off the main steam for some reason, such as the main steam isolation valves 12 and 13 being fully closed, the pressure rises and the voids generated in the core are crushed, increasing the deceleration effect. Will be done. In response to this, the output of the nuclear reactor also rises. Further, when the pressure rises to a certain set point, the relief safety valve 21 is actuated to release the shut off main steam into the pool water 4 in the pressure suppression chamber 5 to suppress the pressure rise.

In this way, when a transient change occurs due to the rapid increase in the pressure of the turbine main steam control valve, the turbine main steam stop valve, and the main steam isolation valve, the output and the pressure increase. In order to suppress the
It detects the 0% stroke position and safely shuts down the reactor.

However, the probability of occurrence is very small and usually need not be considered, but when scram by the reactor safety protection system fails during transient change (abbreviated as ATWS above).
In response to the high reactor pressure signal, the recirculation pump trip signal is activated and the recirculation pump is stopped. Then, the output is suppressed by decreasing the core flow rate and increasing the core void rate. Even if the output is suppressed in this way, since the output is still maintained, main steam is continuously released from the relief safety valve 21, and the pool water temperature in the pressure suppression chamber 5 continues to rise. Therefore, in such a case, the boric acid water injection system can be manually operated to inject boric acid water into the core to add a negative reactivity to finally stop the reactor.

When the main steam is shut off, there is no return water to the condenser, so the supply of water will be lost when the main steam is shut off, and thereafter the high pressure emergency core cooling system (high pressure core spray system, high pressure injection system) Water injection is continued to maintain the reactor water level. At this time, even if this high-pressure emergency core cooling system does not operate, the low-pressure core cooling system (low-pressure core spray system, low-pressure water injection system) as a reserve is configured to inject water to maintain the water level. .

[0007]

However, since this low-pressure emergency core cooling system was originally designed assuming a coolant loss accident, after the start of water injection, water injection is continued without stopping as much as possible. ing. Further, since the low pressure emergency core cooling system has a large capacity, the reactor is filled with water in a short time after the start of water injection.

Therefore, when the low-pressure emergency core cooling system operates while the boric acid water system is operating, the reactor is filled with water and the injected boric acid escapes through the safety valve due to the above reasons. -There was a risk that she would be washed away. The present invention has been made to solve the above problems, and an object of the present invention is to obtain a boric acid outflow prevention device that can prevent the flow of boric acid water.

[0009]

In order to achieve the above object, the first aspect of the present invention is to start a water injection pump of a low pressure emergency core cooling system for injecting a coolant into a reactor core in the event of an accident. A start signal and a second start signal for starting a water injection pump of a boric acid water injection system for injecting boric acid water into the core when a control rod is not inserted into the core at the time of an accident;
When three signals of a reactor water level high signal transmitted when the reactor water level in the reactor pressure vessel accommodating the reactor core exceeds a predetermined value, the low pressure emergency core cooling system Provided is a boric acid outflow prevention device characterized by transmitting a stop signal for stopping water injection to a core.

[0010]

In the boric acid outflow prevention device configured as described above, after the boric acid water is injected into the reactor and the cooling water is injected from the low pressure emergency core cooling system, the reactor water level is set to a predetermined value. When the above is reached, water injection from the low pressure emergency core cooling system is stopped. Therefore, the boric acid released from the boric acid water injection system is not released to the outside of the system due to full water in the reactor, so that it is effectively retained in the reactor.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the boric acid outflow prevention device according to the present invention will be described below with reference to FIG.

In FIG. 1, a low-pressure core spray system operation signal 40 and a low-pressure water injection system operation signal 41, which are operation signals of the low-pressure core cooling system, which are transmitted when the water level in the reactor pressure vessel falls below a certain value. 42 is input to the OR gate 43.
The output signal 44 of the OR gate 43 and the boric acid water injection system operation signal 45 for operating the boric acid water injection system are input to the AND gate 46. The output signal 47 of the AND gate 46 and the reactor water level high signal 48 output when the water level in the reactor pressure vessel is higher than the main steam pipe nozzle position are input to the AND circuit 49.
The AND circuit 49 outputs the low pressure emergency core cooling system stop signal 50 when both conditions are met.

Therefore, when the low-pressure emergency core cooling system stop signal is issued, the injection of water into the low-pressure emergency core cooling system is stopped, the rise of the water level is stopped, and the coolant of the reactor does not flow out from the main steam pipe nozzle. Are held in the reactor.

[0014]

As is apparent from the above description, in the boric acid outflow prevention device of the present invention, the high pressure emergency core system does not function for some reason during ATWS, and the low pressure emergency core system must depend on water injection only. The excellent effect of preventing the outflow of boric acid out of the reactor is obtained when it is necessary.

[Brief description of drawings]

FIG. 1 is a block diagram of a logical operation unit incorporated in an embodiment of a boric acid outflow prevention device according to the present invention.

FIG. 2 is a schematic system diagram showing a conventional example of a boiling water nuclear power plant.

[Explanation of symbols]

2 ... Reactor pressure vessel 7 ... Core 11 ... Main steam pipe 23 ... Low pressure core spray pump 25 ... Low pressure core spray pipe 27 ... Boric acid water injection pipe 28 ... Boric acid water injection tank 29 ... Low pressure water injection pump 30 ... Low pressure water injection pipe

Claims (1)

[Claims] 1. A first start signal for starting a water injection pump of a low pressure emergency core cooling system for injecting a coolant into a reactor core at the time of an accident, and a core when a control rod is not inserted in the core at the time of the accident. A second activation signal for activating a water injection pump of a boric acid water injection system for injecting boric acid water into the reactor, and a signal when the reactor water level in the reactor pressure vessel accommodating the core exceeds a predetermined value. A boric acid outflow prevention device, which transmits a stop signal for stopping water injection into the core of the low-pressure emergency core cooling system when three signals of the reactor water level high signal are simultaneously transmitted.