JPS6375691A - Natural circulation type reactor - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to natural circulation nuclear reactors, and is particularly suitable for application to boiling water reactors in the event of a loss of coolant accident and control rod insertion in the event of a control rod insertion. This invention relates to a natural circulation nuclear reactor equipped with an emergency core cooling system that can ensure core cooling in the event of a power outage.

[Prior Art] Figure 2 shows the emergency core cooling system of a conventional natural circulation nuclear reactor.

In this nuclear reactor, a pool 14 storing water is installed above the reactor containment vessel 13. The reactor core 2 inside the reactor pressure vessel 1 is structured so that it is located below the pool 4.
In the event of an accident, water can be injected into the reactor core 2 from the pool 14 by falling due to gravity. Furthermore, an isolation condenser 15 is installed in the pool 14 to condense the steam in the reactor pressure vessel 1 to remove heat, and a pressure relief valve 7 is installed between the main steam pipe and the pool 14. There is.

In the event of a loss of coolant accident, the steam in the reactor pressure vessel 1 is released into the pool 14 by the pressure relief valve 7, the pressure is reduced, and water is injected into the reactor core by gravity fall.

[Problems to be solved by the invention] In the above-mentioned conventional technology, the emergency core cooling system considers water injection into the reactor core by gravity falling from a pool, but this water injection is only for the purpose of maintaining the submergence of the reactor core. Ta.

The purpose of the present invention is to reduce dynamic equipment and improve reliability by combining a pressure relief valve in a reactor pressure vessel with a plurality of tanks storing pressurized water or boric acid water.
The objective is to provide an emergency core cooling system that has an effective combination to safely shut down and cool the core in the event of a loss of coolant accident or in the unlikely event that a control rod cannot be inserted. Means for Achieving] The above objective is achieved by the following two points.

1) Reduce dynamic equipment and increase reliability by combining a pressure relief valve with a pressurized tank or a tank placed above the pressure vessel to account for gravity fall.

2) Combining a pressurized tank or a gravity drop water tank and injecting boric acid water into some of the tanks will deal with coolant loss accidents and the unlikely event that a control rod cannot be inserted.

[Operation] It becomes possible to combine the pressure relief valve provided in the main steam pipe of the reactor with a pressurized tank or a gravity drop water tank. In addition, this injection uses the natural force of tank pressurization or gravity falling, so it is more reliable than water injection using a pump.

In addition, by injecting mature wood into some of the multiple tanks, it is possible to improve control in the event of a nuclear reactor with poor self-control, where the void reactivity in the reactor core is zero or negative. If the rod cannot be inserted, boric acid water can be injected, making it possible to safely shut down the reactor.

[Example] FIG. 1 shows an example of the present invention. The present invention will be described below with reference to Examples.

In the embodiment of the present invention, a boiling water reactor type natural circulation nuclear reactor is considered. A natural@ring type nuclear reactor has a reactor pressure vessel 1 which has a reactor core 2 that generates heat due to a nuclear fission reaction, a main steam pipe 3 that sends steam generated in the reactor core 2 to a turbine 5, and a condenser 6 that recycles condensed water. It consists of a water supply pipe 4 that supplies water to the reactor pressure vessel 1. The flow of water inside the reactor pressure vessel 1 is caused by the water supplied by the water supply pipe 4 being naturally connected to the shroud 11 by the ring.
The steam passes through the outside of the reactor core, reaches the lower part of the reactor core, receives heat in the reactor core 2, becomes steam, and is supplied to the turbine 5 through the main steam pipe 3.

In this embodiment, a pressure relief safety valve 7 is provided in the main steam pipe 3, and the steam discharged from the relief valve 7 is condensed in a suppression chamber 8. In addition, as a response to an accident, boric acid water is stored in a low-pressure water injection tank 9 with an internal pressure of about 2 to 5 atm, which is placed above the FA child reactor pressure vessel 1 and can inject water into the pressure vessel 1 by falling due to gravity. The reactor pressure vessel 1 is composed of high-pressure water injection tanks 10 with an internal pressure of about 5 to 10 atmospheres, and these tanks are connected to the reactor pressure vessel 1 by injection piping.

An example of the operation of the system of the present invention during a loss of coolant accident (LOCA) will be described below.

A loss of coolant accident is caused by a rupture in the piping connected to the reactor pressure vessel 1, causing the coolant inside the pressure vessel 1 to leak to the outside.If water is not injected into the reactor core, the reactor core will be exposed and the integrity of the reactor core will be compromised. This was an accident that resulted in damage to the equipment.

In the present invention, a high pressure water injection tank 10 is used as a water injection function to the reactor core.
Although a low-pressure water injection tank 9 is provided, the internal pressure is low, so it is necessary to reduce the pressure inside the reactor pressure vessel 1 in order to operate this equipment.

In the present invention, by opening the pressure relief safety valve 7, the steam in the reactor pressure vessel 1 is kept submerged in water.

In addition, in a boiling water reactor, if the reactor deviates from normal operating conditions for some reason, control rods are inserted to shut down the reactor, but in the unlikely event that the control rods cannot be inserted, As the number of voids in the reactor core increases, the nuclear reaction inside the reactor core will be suppressed. However, even if we assume that the reactivity due to these voids is O or negative, it is still very small. In the present invention, after the pressure is reduced by operating the pressure relief safety valve 7, the reactor can be safely stopped by injecting water into the high-pressure water injection tank 10.

Note that in this embodiment, two large-capacity low-pressure water injection tanks 9 are provided to maintain the reactor core flooding, and a low-volume high-pressure water injection tank 10 is provided to control the core output. The capacity of the high-pressure water injection tank can be optimized based on the amount of water that can safely shut down the reactor.

FIG. 4 shows another embodiment of the invention.

In this embodiment, the reactor isolation cooling system (RCIC) 12, which is a combination of the present invention and the reactor solar radiation cooling system 12, is used when condensate water and water supply are stopped for some reason after the reactor is shut down. In order to maintain the reactor water level, the purpose is to inject water from the suppression chamber 8 into the reactor core 2 using a turbine-driven pump that uses part of the reactor steam. Water injection is possible.

The operation of the system in the event of a loss of coolant accident according to this embodiment will be described below.

In the previous embodiment, the operating pressure of the high pressure water injection tank 10 was RCI
("l: It was lower than the pump pressure, so a significant depressurization was necessary. However, in this example, the shutoff pressure of the RCIC pump is high, so it is possible to inject water at a time when the pressure is high, and as a result, the reactor pressure drops.

In combination with the low-pressure water injection tank 9, the core can be maintained submerged even in the event of a loss of coolant accident.

Further, in this embodiment, the high-pressure water injection tank is used to safely stop the reactor only if the control rods cannot be inserted for some reason.

[Effect of the invention] According to the present invention, there are the following effects.

Engineering) Reduce dynamic equipment such as pumps from the emergency core cooling system,
It has a highly reliable ECC5 configuration.

2) Even if the void reactivity in the core is zero or negative, it is possible to safely shut down the reactor in a very small natural circulation reactor in the unlikely event that a control rod cannot be inserted.

3) By providing a plurality of water injection tanks, it is possible to change the purpose of operation of this tank by changing the injection pressure, tank capacity, and water in the tank.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram of an ECC 5 of a conventional natural circulation reactor. FIG. 3 is a block diagram of another embodiment of the present invention. 1... Reactor pressure vessel, 2... Reactor core, 3... Main steam pipe, 4... Water supply pipe, 5... Turbine, 6... Condenser, 7... Pressure relief Safety valve, 8... Suppression chamber, 9... Low pressure water injection tank, 10... High pressure water injection tank, 11... Shroud, 12... Reactor alternate cooling system, 13... Reactor containment Container, 14...
Pool, 15...Isolation capacitor
：、－＼E；ト：、”：に51 Agent Patent attorney Katsuma Ogawa ”：u：Jth is X2 Ennon

Claims (1)

[Claims] 1. In a boiling water reactor consisting of a pressure vessel, a reactor core, and a shroud surrounding the reactor core, in the event of a loss of coolant accident or when it is difficult to shut down the reactor due to the inability to insert control rods, the reactor pressure vessel A pressure relief safety valve is designed to promote depressurization within the pressure vessel by releasing the steam inside the vessel, and a pressure relief valve that stores water pressurized to a pressure that allows water to be injected into the pressure vessel through gravity fall after depressurization of the pressure vessel. A natural circulation nuclear reactor characterized by an emergency core cooling system consisting of a tank. 2. In claim 1, a plurality of tanks storing water are provided, one of which stores boric acid water, and an emergency core cooling system is provided in which each tank has a different capacity and pressure. A natural circulation nuclear reactor featuring 3. A natural circulation nuclear reactor according to claim 1 or 2, characterized in that the void reactivity in the reactor core is zero or small and negative.