JPH0377096A - Vent device of reactor container - Google Patents

Abstract

PURPOSE:To attenuate the radioactivity of fission products by providing a scrubbing piping which introduces the gap in a wet well to the vapor phase part of a hermetic vessel, a dry well connecting piping, a release piping, a connecting piping for releasing the gas in the hermetic vessel, etc. CONSTITUTION:The vapor phase part of the wet well 4 and the liquid phase part of the hermetic vessel 10 are connected by the scrubbing piping 6. A scrubbing valve 7 which is operated to open when the pressure in the reactor container rises is installed to this piping 6. The vapor phase parts of the dry well 2 and the vessel 10 are connected by the dry well connecting piping 8 and the connecting pipe 9 to discharge the gas from the dry well 2 to the vessel 10 when the pressure in the reactor container rises are installed to this piping 8. Water 11 for scrubbing is housed in the vessel 10 and the fission products are removed when the gas introduced from the dry well 2 or the wet well 4 passes the water 11. The vapor phase part of the vessel 10 and the atm. releasing port 15 are connected by the connecting piping 16 and a stop valves 12 are installed to this piping 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a nuclear reactor containment vessel venting device used in a nuclear power plant.

(Prior art) Reactor containment vessels used in nuclear power plants isolate the reactor from the outside environment in the event of an accident and prevent radioactive fission products (hereinafter referred to as FP) from being released outside the reactor pressure vessel. Even in such cases, it is installed to act as a barrier to the release of FP into the external environment and to prevent radioactivity from being released into the external environment.

The reactor containment vessel of a boiling water reactor (hereinafter referred to as BWR) is generally divided into two compartments: a dry well and a wet well. The reactor pressure vessel is housed in the dry well, and the pressure suppression vessel is housed in the wet well. Water is stored. An accident in which piping connected to the reactor pressure vessel ruptured and high-temperature, high-pressure primary cooling water was released into the dry well (
During LOCA (hereinafter referred to as LOCA), the atmospheric gas mainly composed of water vapor in the dry well is guided into the pressure suppression water via the vent pipe, where it is cooled and condensed, thereby suppressing the pressure rise inside the reactor containment vessel. . In addition, in the event of a LOCA, the emergency core cooling system is activated to replenish the lost primary cooling water, ensuring core cooling, and at the same time, the decay heat removal system is activated to remove heat from the pressure suppression water. Temperature rise is suppressed.

In a nuclear power plant with such a reactor containment vessel, an abnormal event occurs, which is impossible in reality, and the means of supplying cooling water to the reactor pressure vessel is lost for both regular and emergency purposes. Assuming an accident in which the core cooling function is completely lost, or an accident in which the heat removal function from the reactor containment vessel is completely lost (hereinafter referred to as a "severe accident"), the safety of the nuclear power plant is still lost. Measures may be taken to prevent this from happening.

If we assume a severe accident in which the reactor core cooling function is completely lost, the reactor core will be heated by decay heat and the core will melt, penetrating the reactor pressure vessel and falling into the lower pedestal of the reactor pressure vessel.

The fallen molten core reacts with the concrete in the lower pedestal, generating a large amount of non-condensable gases such as CO and H2, and at the same time raising the temperature inside the dry well and increasing the internal pressure of the dry well. As the internal pressure of the dry well increases, it is guided to pressure suppression water via the atmosphere guide vent pipe, but since the main component of the atmospheric gas is a non-condensable gas, it does not condense and no pressure suppression effect can be expected. The wet well internal pressure also increases. As a result, the reactor containment vessel will be damaged by overpressure, and a large amount of FP within the reactor containment vessel will be released into the environment.

Furthermore, in the event of a severe accident in which the heat removal function is completely lost from the reactor containment vessel, the core cooling function is intact and the core is cooled. However, as high-temperature steam generated by decay heat in the reactor core is continuously released into the pressure suppression water, the temperature of the pressure suppression water rises, eventually reaching a saturation temperature and losing its pressure suppression effect.

After that, the temperature and pressure inside the reactor containment vessel continued to rise, leading to overpressure damage. If the reactor containment vessel is damaged, there is a high possibility that the emergency core cooling system, which uses pressure suppression water as a water source, will lose its functionality. In this case, the core cooling function is lost, core melting occurs, and FP is released into the reactor containment vessel. Since the reactor containment vessel has already been damaged, FP will eventually be released into the environment.

Probabilistic safety evaluations have shown that the probability of a severe accident occurring is extremely small; however, in view of the importance of the consequences of releasing a large amount of FP into the environment, in recent years many countries have begun to investigate damage to the reactor containment vessel in the event of a severe accident. Devices to prevent this are being considered.

In this way, in each device, before the reactor containment vessel reaches a failure pressure that causes overpressure failure, the FP is removed using a filter, etc., and the atmospheric gas inside the reactor containment vessel is released into the environment. ) It suppresses the increase in the internal pressure of the reactor containment vessel.

For this reason, FP nuclides that cannot be removed by filters, such as radioactive rare gases, are directly released into the environment, and furthermore, it is necessary to release them into the environment before the reactor containment vessel is overpressured. Therefore, there is little time to spare and it is not possible to expect a radioactivity attenuation effect. As a result, there was a risk that highly radioactive rare gases would be released into the environment when the containment vessel was vented in the event of a severe accident.

(Problems to be Solved by the Invention) As described above, in the event of a severe accident, there is a risk that a large amount of FP whose reactor containment vessel has been damaged due to overpressure may be released into the environment. Although the probability of this severe accident occurring is extremely small, considering the importance of the consequences, it is necessary to maintain the integrity of the reactor containment vessel and prevent a large amount of FP from being released.

However, in the case of reactor containment vessel venting devices that have recently been proposed in other countries as a measure to prevent overpressure damage, when the internal pressure of the reactor containment vessel is reduced (during venting), it is possible to directly release Because there is FP released,
There was a risk that highly radioactive noble gases would be released into the environment.

The purpose of the present invention is to reduce the internal pressure of the reactor containment vessel in the event of a severe accident at a nuclear power plant without exceeding the standard value of exposure dose in the case of a hypothetical accident in the site evaluation review guidelines, to ensure its integrity and to protect the environment of the FP. An object of the present invention is to provide a reactor containment vessel venting device that can prevent the release of a large amount of.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a liquid phase section in which scrubbing water is stored in the lower part installed adjacent to the reactor containment vessel. a scrubbing pipe that connects the wet well gas phase part of the reactor containment vessel and the airtight container and leads the gas in the wet well to the liquid phase part of the airtight container, and a scrubbing pipe installed in this scrubbing pipe that is normally closed. A scrubbing valve that opens when the internal pressure of the reactor containment vessel increases, a dry well connection piping that connects the dry well of the reactor containment vessel and the airtight vessel and guides the gas in the dry well to the liquid phase part of the airtight vessel, and this dry well. A communication valve installed in the communication pipe that is normally closed and opens when the internal pressure of the reactor containment vessel rises is connected to the scrubbing pipe and dry well communication pipe to the atmosphere release port to release gas in the dry well or wet well. A discharge pipe that leads directly to the atmosphere release port, and a pipe that is installed in this discharge pipe and is normally closed, but is opened when the gas in the dry well or wet well is released directly from the atmosphere release port to the external environment when the internal pressure of the reactor containment vessel increases. a discharge valve that operates, a connecting pipe that connects the gas phase part of the airtight container and the atmosphere release port and guides the gas in the airtight container to the atmosphere release port;
It is an object of the present invention to provide a reactor containment vessel venting device characterized by comprising an on-off valve installed in the communication pipe and normally closed and opened when the internal pressure of the airtight vessel rises.

(Function) During a severe accident, when the reactor core welds and melts through the reactor pressure vessel, fission products are released into the dry well of the reactor containment vessel, and at the same time the dry well internal pressure rises, nuclear fission within the dry well occurs. The product-containing gas passes through the pressure suppression water via a vent pipe and is then led to the wetwell gas phase. When gas containing fission products passes through pressure-suppressed water, the fission products are removed as they form bubbles and rise through the water (scrubbing effect).

In the reactor containment venting device constructed in the present invention, before the reactor containment vessel internal pressure reaches the failure pressure, the gas in the wet well is discharged to the scrubbing pipe connecting the wet well gas phase and the airtight vessel. By opening the installed scrubbing valve, it is introduced into the liquid phase part of the airtight container via the scrubbing pipe. The gas that has reached the liquid phase portion of the airtight container rises in the form of bubbles through the scrubbing water, and after fission products are removed, it reaches the gas phase portion of the airtight container. This gas flow also increases the internal pressure of the airtight vessel, so before the internal pressure of the airtight vessel or the reactor containment vessel reaches the failure pressure, it is necessary to install a By opening the release valve, the gas in the gas phase portion of the airtight container is guided to the atmosphere release port via the release piping, and is released into the outside environment.

Furthermore, if the water level in the wet well rises during the course of a severe accident and the piping connecting the wet well gas phase and the airtight container is submerged, it is necessary to connect the gas in the dry well between the dry well and the airtight container. By opening the communication valve installed in the dry well communication pipe, the liquid is introduced into the liquid phase part of the airtight container via the dry well communication pipe. What happened after that was
This is similar to the case where gas is introduced from the gas phase part of the wet well to the liquid phase part of the airtight container.

Furthermore, although the core cooling function is sound and the integrity of the reactor core is ensured, if the decay heat removal function is lost and the internal pressure of the reactor containment vessel increases although no fission products are released, the internal pressure of the reactor containment vessel increases. The gas is directly discharged to the outside environment from the atmosphere discharge port via the discharge piping.

In this way, if the gas inside the reactor containment vessel contains fission products, the fission products are removed by scrubbing and the radioactivity is attenuated by temporarily storing them in an airtight container before being released to the outside environment. discharge. As a result, in the event of a severe accident, the reactor containment vessel can be vented without exceeding the standard value of exposure dose in the case of a hypothetical accident in Japan's site evaluation review guidelines, the internal pressure of the reactor containment vessel has been reduced, and its integrity has been ensured, and nuclear fission It becomes possible to prevent large amounts of product from being released into the environment.

(Example) An embodiment of the present invention will be described below with reference to FIG.

A reactor containment vessel 20 disposed within a reactor building 19 is divided into two compartments: a dry well 2 and a wet well 4. The reactor pressure vessel 1 is housed in the dry well 2, and the pressure suppression water 4 is housed in the wet well 4. A vent pipe 3 is installed between the dry well 2 and the wet well 4 to guide the gas inside the dry well 2 into the pressure suppression water 4 when the internal pressure of the dry well increases. Gas in the wetwell 4 gas phase is transferred to an airtight container 1
The gas phase portion of the wet well 4 and the liquid phase portion of the airtight container 10 are connected by a scrubbing pipe 6 in order to introduce the scrubbing water into the scrubbing water 1 in the wet well 4. A scrubbing valve 7 is installed in the scrubbing pipe 6, which is normally closed and is opened when the reactor containment vessel pressure increases. Further, in order to guide the gas in the dry well 2 into the scrubbing water 11 in the airtight container 10 when the wet well 4 is flooded, the liquid phase portions of the dry well 2 and the airtight container 10 are connected by a dry well connection piping 8. be done. A communication valve 9 is installed in the dry well communication pipe 8, which is normally closed and is opened when it is necessary to drain gas from the dry well 2 to the airtight vessel IO when the pressure of the reactor containment vessel increases.

In FIG. 1, a part of the scrubbing pipe 6 and the scrubbing connecting pipe 8 are shared, but it is also possible to install them separately. Further, although each of the scrubbing valve 7 and the communication valve 9 is configured as two valves in series, it is also possible to use one valve each, and it is also possible to use a rubber disc or the like as a substitute for the valve.

Scrubbing water 11 is stored in the airtight container IO,
When the gas introduced from the dry well 2 or wet well passes through the scrubbing water 11, fission products are removed. In order to discharge the gas in the gas phase portion of the airtight container 10 to a high place in the external environment, the gas phase portion of the airtight container 10 and the atmosphere discharge port 15 are connected by a connecting pipe 16. An on-off valve 12 which is normally closed and opens before the reactor containment vessel 20 pressure or the airtight vessel 11 pressure reaches the failure pressure is installed in this communication pipe 1B.

Furthermore, when the internal pressure of the reactor containment vessel 20 increases although the fission products are not released, the gas in the dry well 2 or wet well 4 is released directly to the environment.
A discharge pipe 13 and a discharge valve 14 are installed to connect the gas phase part of the dry well 2 or wet well 4 to the atmosphere discharge port (exhaust tower) 15.

Although the discharge pipe 13 shares a part with the pipes 6, 8, and 11, it is also possible to have an independent configuration in which the pipes 6, 8, and 11 do not share the same part. Further, although each of the on-off valve 12 and the discharge valve 14 has a configuration of two valves in series, it is also possible to have one valve each.

In addition, each valve in the figure can be used in various ways, such as using a DC electric valve, an air-operated valve, or a loveture disc, so that it can function even in the event of a total AC power loss.

[Effect of the invention] A severe accident occurs in a nuclear power plant equipped with the reactor containment venting device according to the present invention, and nuclear fission products having radioactivity are released into the reactor containment vessel, and at the same time the internal pressure rises. If the failure pressure is likely to be exceeded, the gas inside the reactor containment vessel is temporarily kept in an airtight container to attenuate the radioactivity of all fission products, including rare gases. Furthermore, the gas in the reactor containment vessel is passed through scrubbing water in the airtight vessel, and the scrubbing effect at that time removes radioactive fission products.

As a result, in the event of a severe accident, the reactor containment vessel can be vented without exceeding the standard value for exposure dose in a hypothetical accident in Japan's site evaluation review guidelines, and the pressure of the reactor containment vessel can be reduced to ensure its integrity. Large amounts of radioactive fission products can be prevented from being released into the environment.

[Brief explanation of drawings]

FIG. 1 is a schematic system diagram of a reactor containment vessel venting device according to an embodiment of the present invention. 1... Reactor pressure vessel 2... Dry well 3... Benk pipe 4... Wet well 5... Pressure suppression water 6... Scrubbing piping 7... Scrubbing valve 8... Dry Well communication pipe 9...Communication valve IO...Communication valve 11...Scrubbing water 1B...Communication pipe 19...Reactor building 20...Reactor containment vessel 12...Opening/closing valve 14. ...Discharge valve 13...Discharge piping 15...Atmospheric discharge port

Claims (1)

[Claims] An airtight container that is installed adjacent to the reactor containment vessel and has a liquid phase section storing scrubbing water at the bottom, and an airtight container that connects the wet well gas phase section of the reactor containment vessel and the airtight container to transport the gas in the wet well. A scrubbing pipe that leads to the liquid phase, a scrubbing valve that is installed in this scrubbing pipe and is normally closed and opens when the internal pressure of the reactor containment vessel increases, and a scrubbing valve that connects the dry well of the reactor containment vessel and the airtight vessel. A dry well connecting pipe that leads the gas to the liquid phase part of the airtight vessel, a connecting valve installed in this dry well connecting pipe that is normally closed and opens when the internal pressure of the reactor containment vessel rises, and this scrubbing pipe and dry well A discharge pipe that connects the communication pipe and the atmospheric discharge port and leads the gas in the dry well or wet well directly to the atmospheric discharge port, and a discharge pipe that is installed in this discharge pipe and is normally closed when the internal pressure of the reactor containment vessel increases. A release valve that opens when the gas in the wet well is released directly to the outside environment from the air release port, and a connection that connects the gas phase part of the airtight container and the air release port to guide the gas in the airtight container to the air release port. A reactor containment vessel venting device comprising a pipe and an on-off valve installed in the connecting pipe, which is normally closed and opens when the internal pressure of the airtight vessel increases.