JPS62237395A - Emergency core cooling device - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an emergency core cooling system used in a nuclear power plant.

(Prior technology) When a rupture of the reactor pressure vessel boundary occurs in a nuclear power plant, resulting in a loss of coolant accident, in conventional nuclear reactors, an emergency core cooling system using a pump, which is a dynamic device, is used. (hereinafter abbreviated as ECC5) is used to cool the core and ensure its integrity. That is, in the case of a small-diameter rupture (hereinafter abbreviated as small LOGA), there is little coolant flowing out from the rupture port, and the reactor pressure is maintained at a high pressure. Therefore, in this case, by injecting cooling water into the reactor using the high-pressure ECC 5, cooling can be performed without exposing the reactor core. On the other hand, in the case of a large-diameter rupture (hereinafter abbreviated as large LOCA), a large amount of cooling water flows out from the rupture port and is temporarily exposed in the reactor core, causing a significant drop in reactor pressure. However, in this case, by injecting cooling water into the reactor using the large-capacity, low-pressure ECC 5, it is possible to re-flood the reactor core and ensure cooling. In the latter case, the situation is more severe than in the former case, but the maximum temperature of the fuel cladding tube is kept sufficiently lower than the limit value.

On the other hand, in recent years, from the viewpoint of streamlining ECC5 and improving reliability, the practical application of a nuclear reactor having an emergency core cooling system as shown in FIG. 3 has been proposed.

In addition, the emergency core cooling system shown below is
This is called the dPool method. Here, a conventional emergency core cooling system will be explained with reference to FIG. In FIG. 3, a reactor core 2 is housed within a reactor pressure vessel 1. As shown in FIG. A dry well 3 is formed around the reactor pressure vessel 1, and a pool 5 for storing a coolant 4 is arranged on the upper side of the dry well 3. Above these pools 5, there is provided an upper structure 6 that forms a fuel exchange area. Further, a water supply pipe 7 is connected to the reactor pressure vessel 1 through the dry well 3, and coolant is supplied to the water supply pipe 7 from the pool 5 via a check valve 8 in the event of an accident. A coolant injection pipe 9 leading into the pipe 7 is connected.

In the above configuration, the pool that serves as the cooling water source is located above the reactor, so coolant can be injected into the reactor by the difference in the coolant head without using a pump like in the conventional ECC5. . Therefore, the ECC 5 does not use a pump, which is a dynamic device, and is composed only of static devices such as piping, ascending, etc., and therefore has the advantage of high reliability and low cost.

However, as mentioned above, in the case of a small LOCA, the reactor pressure is maintained at a high pressure (approximately 70 kg/cot), so the E
It is impossible to inject coolant into the reactor using only the weight of the coolant in the levated pool. Therefore, E
Small LO in a levated pool reactor
When a CA occurs, the steam inside the reactor is released to the outside by an automatic decompression device to lower the reactor pressure, and then
Inject the vated pool coolant into the reactor.

During the depressurization process using an automatic decompression device, the core is temporarily exposed, but the core is then re-submerged with water by injection of coolant, ensuring cooling.

(Problem to be solved by the invention) When assuming that a loss of coolant accident occurs in a nuclear reactor with an elevated pool type containment vessel, a small LOCA is expected to occur relatively more frequently than a large LOCA. In the case of LOCA, coolant from the Elevated Pool can only be injected into the reactor after the reactor pressure is reduced using an automatic decompression device. Despite the small LOCA during this depressurization process, the reactor core is temporarily exposed, and although the core is eventually re-flooded and core cooling is ensured, the reactor core is relatively likely to occur during a small LOCA. Exposure is an undesirable problem.

The purpose of the present invention is to prevent core exposure by injecting cooling water into the reactor without depressurizing the reactor during a small LOCA in a nuclear reactor equipped with an elevated pool type emergency core cooling system, thereby maintaining the health of the reactor core. An object of the present invention is to provide an emergency core cooling system that can ensure safety.

[Structure of the invention]

(Means for solving problems) In order to achieve the above object, in the present invention.

a high-pressure tank arranged adjacent to the pool and connected to the reactor pressure vessel via a coolant injection pipe; a gas phase part of the high-pressure tank; and a gas phase part of the reactor pressure vessel. a pressurized pipe that connects the high pressure tank and has a valve that opens only when injecting from the high pressure tank to the reactor pressure vessel;
a pressure reducing pipe having one end connected to the upper part of the high pressure tank and the other end open to the liquid phase part of the pool and having a valve that opens when the cooling water in the high pressure tank falls below a certain value;
An emergency core cooling system is provided, comprising a coolant supply pipe connecting the liquid phase part of the tank and a high-pressure tank.

(Function) In the emergency core cooling system configured in this way, in the case of an event where the reactor pressure is maintained at a high pressure and the reactor water level drops, such as during a small LOCA or a feed water loss transient, Coolant is supplied into the reactor by applying reactor pressure as back pressure to a high-pressure tank storing coolant. Furthermore, if the coolant stored in the tank is depleted, the pressure supply from the reactor is first isolated and then the tank is depressurized.
The coolant stored in the Pool is injected into the high pressure tank by its own weight. If two or more systems consisting of such high-pressure tanks are installed, even if one high-pressure tank is replenishing cooling water from the Elevated Pool, cooling water can be injected into the reactor from the remaining tank. ,
Water can be continuously injected into the reactor.

In this way, high-pressure cooling water can be continuously injected into the reactor, so the reactor pressure is maintained at a high level and the reactor water level drops during a small LOCA, during a feed water loss transient, etc. 6. (Example) An example of the present invention will be described below with reference to FIG. 1. Note that in FIG. 1, the same parts as in FIG. 3 are given the same reference numerals, and explanations of their configurations will be omitted.

As shown in FIG. 1, a reactor pressure vessel 1 containing a reactor core 2
There is a pool above. A high pressure tank 10 is installed adjacent to this pool 5.

This high pressure tank 10 includes a coolant injection pipe 11 for injecting coolant into the reactor pressure vessel 1, and a check valve 12.
is provided. Further, when the coolant inside the high-pressure tank 10 is depleted, a coolant replenishment pipe 13 and a check valve 14 connect the liquid phase part of the pool 5 and the high-pressure tank 10 in order to replenish the coolant from the pool 5. are connected and provided. However, when replenishing the high-pressure tank 10 with the coolant from the pool 5, it is necessary to temporarily lower the internal pressure of the high-pressure tank 10. A depressurizing pipe 15 and an electric valve 16 for discharging high pressure gas in the air conditioner 10 are provided.

In addition, in order to additionally pressurize the high-pressure tank 10 to the same pressure as the internal pressure of the reactor pressure vessel 1 while the high-pressure tank 10 is being supplied with coolant, the gas phase part of the high-pressure tank 10 is A pressurizing pipe 17 and an electric valve 18 are provided. In order to prevent fatigue caused by reactor steam flowing into the high-pressure tank 10 via this pressurizing pipe 17, a float 19 made of highly insulating ceramics is arranged at the gas-liquid interface in the high-pressure tank IO.

The inner surface of the high-pressure tank 10 is also coated with highly insulating ceramic to prevent fatigue due to thermal cycles within the high-pressure tank 10.

In a reactor equipped with such an emergency core cooling system, an event such as an OCA or feed water loss transient in which the reactor pressure is maintained at a high pressure and the reactor water level drops occurs. If the reactor pressure is applied as back pressure to the high-pressure tank storing cooling water by opening the electric valve of the pressurizing pipe, cooling water will be supplied into the reactor pressure vessel due to the water head difference between the high-pressure tank and the reactor. Ru. Furthermore, when the cooling water stored in the high-pressure tank is depleted, first close the electric valve on the pressure piping to isolate the pressure from the reactor, then open the electric valve on the pressure reduction piping to reduce the high pressure. The tank is depressurized, the check valve on the coolant supply pipe is opened, and the coolant is injected into the high-pressure tank using the water head difference from the pool. Next, the valve of the pressure reducing pipe is closed and the electric valve on the pressurizing pipe 10 is opened to apply additional pressure to the high pressure tank equal to the reactor pressure. Furthermore, since the valve of the coolant supply pipe is a check valve, it is automatically closed at this time.

When the high pressure tank is pressurized by the reactor pressure.

Coolant can be injected into the reactor through the coolant injection pipe using the water head difference between the high-pressure tank and the reactor pressure vessel. In addition, in order to automate such a series of operations, it is also possible to install a water level gauge in the high pressure tank and interlock the valves of the pressure piping and the valves of the pressure reduction piping.

Furthermore, by installing two or more systems consisting of such high-pressure tanks, etc., even when one tank is replenishing cooling water, coolant can be injected into the reactor pressure vessel from the remaining high-pressure tank. This enables continuous supply of coolant.

In this way, high-pressure coolant can be continuously injected into the reactor pressure vessel, so the reactor pressure can be maintained at a high level, and even in the case of a small LOCA where the reactor water level drops, the reactor core can be exposed. This makes it possible to prevent this and at the same time ensure sufficient core cooling.

Furthermore, even in the case of a transient situation in which the reactor pressure is maintained at a high pressure and the yK sub-reactor water level decreases, such as during a feed water loss transient, it is possible to replenish reactor water at a high pressure.

Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same parts as in FIG. 1 are given the same reference numerals, and the explanation of the structure of those parts will be omitted. In FIG. 2, a high pressure tank 1o is provided with a nitrogen gas filling device 2o for constant pressurization. That is, this nitrogen gas filling device 2o includes a nitrogen gas cylinder 21 for storing nitrogen gas, and a compressor 22 for pressurizing the nitrogen gas.
and a nitrogen supply pipe 24 that guides high-pressure nitrogen from the compressor 22 to the high-pressure tank 10 via a check valve 23.

With the above configuration, the emergency core cooling system according to another embodiment of the present invention pressurizes the nitrogen gas in the nitrogen gas cylinder 21 with the compressor 22.
The structure is such that high-pressure nitrogen gas is always sealed into the gas phase portion of the high-pressure tank 10 from 2 through the nitrogen supply pipe 24. Therefore, it is possible to maintain the high pressure tank 10 at high pressure at all times. Therefore, high-pressure coolant can be injected into the reactor pressure vessel 1 without the time delay caused by applying back pressure of the reactor pressure to the gas phase portion of the high-pressure tank 10.

As mentioned above, in a reactor equipped with an emergency core cooling system, if an event occurs in which the reactor pressure is maintained at a high pressure and the reactor water level drops, such as a small LOGA or a transient loss of feed water, nitrogen gas High-pressure cooling water can be immediately injected into the reactor from the pressurized high-pressure tank.
The core cooling performance can be further improved compared to the first embodiment.

〔Effect of the invention〕

According to the present invention, in a nuclear reactor equipped with an emergency core cooling system, during a feed water loss transient or a small LOCA, the reactor water level decreases in this way, and the reactor pressure is maintained at a high pressure. Since it is possible to continuously inject cooling water into the reactor pressure vessel without depressurizing the reactor even in the case of a nuclear reactor, it is possible to prevent core exposure and ensure sufficient cooling of the reactor. I can do it.

[Brief explanation of drawings]

Figure 1 is a schematic system diagram of an emergency core cooling system showing one embodiment of the present invention, Figure 2 is a schematic system diagram of an emergency core cooling system showing another embodiment of the invention, and Figure 3 is an emergency core cooling system diagram showing another embodiment of the present invention. FIG. 2 is a schematic longitudinal sectional view showing a conventional example of a core cooling system. 1...Reactor pressure vessel 2...Reactor core 5...Pool 10...High pressure tank 11...Coolant injection pipe 13...Coolant supply pipe 15...
・Reducing pressure piping 17... Pressurizing piping agent Patent attorney Norihiro Chika Hirofumi Mitsumata Figure 1 Figure 2 Figure a

Claims (1)

[Claims] (1) A reactor pressure vessel that houses the reactor core inside, a pool that is placed above the reactor pressure vessel and holds coolant inside, and a coolant injection pipe that is placed adjacent to the pool. A high pressure tank connected to the reactor pressure vessel, a gas phase part of this high pressure tank and a gas phase part of the reactor pressure vessel are connected, and the opening operation is performed only when injecting from the high pressure tank to the reactor pressure vessel. A pressurized pipe having a valve, and a valve that connects one end to the upper part of the high pressure tank and opens the other end to the liquid phase part of the pool, and opens when the cooling water in the high pressure tank falls below a certain value. 1. An emergency core cooling system comprising: a decompression pipe having a pressure reduction pipe; and a coolant supply pipe connecting a liquid phase portion of the tank and a high pressure tank.