JPH058997B2 - - Google Patents

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, leading to 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 ECCS) is used to cool the core and ensure its integrity. That is, in the case of a small diameter rupture (hereinafter abbreviated as small LOCA), 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 high-pressure ECCS, 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, temporarily exposing the reactor core, and the reactor pressure drops significantly. However, in this case, by injecting cooling water into the reactor using a large-capacity, low-pressure ECCS, it is possible to re-flood the 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 ECCS and improving reliability, the practical application of a nuclear reactor equipped with an emergency core cooling system as shown in Figure 3 has been proposed. In addition, the emergency core cooling system shown below is installed.
This is called the ElevatedPool 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 conventional ECCS. . Therefore, ECCS does not use pumps, which are dynamic equipment, and
Since it is composed only of static equipment such as piping and valves, it 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/ ^cm2 ), so it is not possible to inject coolant into the reactor using only the dead weight of the coolant in the Elevated Pool. It's impossible. Therefore, in an elevated pool reactor,
In the event of a LOCA, automatic depressurization equipment releases steam inside the reactor to the outside to lower the reactor pressure, and then coolant from the Elevated Pool is injected 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 through the injection of coolant, ensuring cooling.

(Problems to be solved by the invention) Assuming that a loss of coolant accident occurs in a nuclear reactor with an elevated pool type containment vessel,
In the case of small LOCA, which is assumed to occur relatively more frequently than large LOCA, coolant from the Elevated Pool can only be injected into the reactor after reducing the reactor pressure using an automatic decompression device. It becomes possible.
During this depressurization process, the core is temporarily exposed despite a small LOCA, and although the core is eventually re-flooded and core cooling is ensured, the core is exposed during a small LOCA, which is relatively likely to occur. 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 ensuring the safety 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 the Problems) In order to achieve the above object, the present invention includes a reactor pressure vessel that houses a reactor core therein, and a reactor pressure vessel that is arranged above the reactor pressure vessel and that has a coolant inside. a high-pressure tank located adjacent to the pool and connected to the reactor pressure vessel side through a coolant injection pipe provided with a check valve that opens the reactor pressure vessel; , a pressurizing pipe connecting the gas phase part of the high pressure tank and the gas phase part of the reactor pressure vessel and having a valve that opens only when injecting from the high pressure tank to the reactor pressure vessel; One end is connected to the upper part, the other end is opened to the liquid phase part of the pool, and when the cooling water in the high pressure tank falls below a certain value, it opens to guide the pressure in the high pressure tank to the pool. A pressure reducing pipe having an on-off valve is connected to the liquid phase part of the tank and the high-pressure tank, and a check valve is disposed on the high-pressure tank side that opens when the on-off valve opens and the pressure inside the high-pressure tank is reduced. The present invention provides an emergency core cooling system characterized by comprising a coolant supply pipe.

(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 transient loss of feed water, 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 Elevated Pool is depleted, first isolate the pressure supply from the reactor and then depressurize the tank, thereby increasing the pressure of the coolant stored in the Elevated Pool under its own weight. Inject into the tank. 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. , it is possible to continuously inject water into the reactor.

In this way, high-pressure cooling water can be continuously injected into the reactor, so the reactor pressure can be maintained at a high pressure and the reactor water level can be lowered.
Even during LOCA, water supply loss transition, etc., it is possible to prevent core exposure and at the same time ensure sufficient core cooling.

(Example) An example of the present invention will be described below based on FIG. In FIG. 1, the same parts as in FIG. 3 are given the same reference numerals, and the explanation of the structure will be omitted. As shown in FIG. 1, a pool is provided above a reactor pressure vessel 1 containing a reactor core 2.
A high pressure tank 10 is installed adjacent to this pool 5. This high pressure tank 10 has a coolant injection pipe 1 for injecting coolant into the reactor pressure vessel 1.
1 and a check valve 12 are provided. Furthermore,
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 when the coolant inside the high pressure tank 10 is depleted. It is 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 pressure reduction pipe 15 and an electric valve 16 are provided to release high pressure gas from the tank 10.

In addition, in order to pressurize the high-pressure tank 10 to a pressure equal to the internal pressure of the reactor pressure vessel 1 while the high-pressure tank 10 is supplied with coolant, the gas phase of the high-pressure tank 10 is transferred from the gas phase of the reactor pressure vessel 1 to the gas phase of the high-pressure tank 10. A pressurizing pipe 17 and an electric valve 18 are provided. In order to prevent fatigue due to reactor steam flowing into the high pressure tank 10 through the pressurizing pipe 17, a float 19 made of highly insulating ceramics is placed at the gas/liquid interface within the high pressure tank 10.

The inner surface of the high-pressure tank 10 is also coated with highly insulating ceramics 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 a small LOCA or a loss of feedwater transient in which the reactor pressure is maintained at a high pressure and the reactor water level drops occurs. case,
When the electric valve in the pressurizing pipe is opened and reactor pressure is applied as back pressure to the high-pressure tank storing cooling water, cooling water is supplied into the reactor pressure vessel due to the water head difference between the high-pressure tank and the reactor. Furthermore, when the cooling water stored in the high-pressure tank is depleted, the electric valve of the pressurized piping is closed to temporarily isolate the pressure from the reactor, and then
The electric valve on the pressure reduction pipe is opened to reduce the pressure in the high pressure tank, and the check valve on the coolant supply pipe is opened to inject cooling water from the pool into the high pressure tank using the head difference. Next, the valve of the pressure reducing pipe is closed and the electric valve on the pressurizing pipe 10 is opened to pressurize the high pressure tank to a pressure 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 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. In addition, even in the case of a transient in which the reactor pressure is maintained at a high pressure and the reactor water level decreases, such as during a transient in which the reactor water is lost, it is possible to replenish the reactor water while maintaining the 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, the high pressure tank 10
is equipped with a nitrogen gas filling device 20 for constant pressurization. That is, this nitrogen gas filling device 2
0 is a nitrogen gas cylinder 21 that stores nitrogen gas
and compressor 2 for pressurizing nitrogen gas.
2, 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 in the gas phase portion of the high-pressure tank 10 from the compressor 22 via 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 LOCA or a transient loss of feed water, nitrogen Since high-pressure cooling water can be immediately injected into the reactor from the high-pressure tank pressurized with gas, 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 having an emergency core cooling system, it is possible to
During LOCA, cooling water can be continuously injected into the reactor pressure vessel without depressurizing the reactor, even when the reactor water level is low and the reactor pressure is maintained at a high pressure. This makes it possible to prevent core exposure and ensure sufficient cooling of the reactor.

[Brief explanation of the drawing]

FIG. 1 is a schematic system diagram of an emergency core cooling system showing one embodiment of the present invention, FIG. 2 is a schematic system diagram of an emergency core cooling system showing another embodiment of the invention, and FIG.
The figure is a schematic longitudinal sectional view showing a conventional example of an emergency 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... Decompression pipe, 17... Pressure piping.

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 pool that is placed adjacent to the pool and that opens on the side of the reactor pressure vessel. A high pressure tank is connected to the reactor pressure vessel via a coolant injection pipe provided with a check valve, and a gas phase part of the high pressure tank is connected to a gas phase part of the reactor pressure vessel. and a pressurizing pipe having a valve that opens only when injecting from the high pressure tank to the reactor pressure vessel, one end connected to the upper part of the high pressure tank, the other end open to the liquid phase part of the pool, and inside the high pressure tank. A pressure reducing pipe having an on-off valve that opens and closes to guide the pressure in the high-pressure tank to the pool when the cooling water of the tank falls below a certain value, and a liquid phase part of the tank and the high-pressure tank are connected to the high-pressure tank. An emergency core cooling system comprising a coolant supply pipe provided with a check valve that opens on the high-pressure tank side when the on-off valve opens and the pressure inside the high-pressure tank is reduced.