JPH04204197A - Emergency core water injection system - Google Patents

Abstract

PURPOSE:To minimize a necessary amount of coolant for the filling of a lower dry well with water by arranging a pool water at a long-time pressure inhibition pool and drawdown water at the bottom of a dry well as two water sources to inject water into a pressure vessel in case a nuclear reactor operates abnormally. CONSTITUTION:A pressure vessel 2 is provided with a reducing valve 9 and a gravity drop pool 10 is set in an internal upper space of a containment vessel 3 as water source of emergency core cooler ECCS11. In a short time after a cooling loss accident LOCA happens, a valve 9 is released to escape steam in the vessel 2 outside a system and water in a pool 10 is injected into the vessel 2 at a head pressure to cool down a core 1. Then, after the cooling of the core 1, the injection water flows out to a dry well 4 to fill a lower space 4 thereof and a lower half of the vessel 2 is emerged under water. Over a long period of time after the LOCA, an equalization system 13 injects the pool water of the pool 5 and/or a drawdown water at the bottom of the well 4 with both of the pool water of a pressure inhibition pool 5 and the drawdown water stored at the bottom of the well 4 both as water source. In other words, the equalization system 13 has two water sources.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an emergency core water injection system for a nuclear reactor, and in particular, for a light water reactor, static means (
Water is injected into the core over a long period of time using water head pressure).
This article relates to an emergency core water injection system that cools the reactor core.

[Conventional technology]

Simplic H7;
pr+u! d 5xfe+7. perlormjn
ce u+d eco++omic(Nuc, En
g, New, 1989. (Known example 1) and JP-A No. 6
3-22390 (publicly known example 2), etc.

In known example 1, when assuming a loss of cooling accident (LOCA), the emergency core cooling system (
This will be carried out in the gravity drop pool of the E CCS), and core cooling for a long period after the accident will be achieved by returning pool water from the pressure suppression pool to the pressure vessel via the pressure equalization system.

For this reason, the pressure equalization system is equipped with a pressure equalization pipe that connects the pressure suppression pool water and the pressure vessel, and in the middle of this pressure equalization pipe there is an explosion valve that is closed during normal operation and opened only in the event of an accident, and a cooling valve inside the pressure vessel. A check valve is installed to prevent material from flowing into the pressure suppression pool. In this case, the water in the containment vessel for a long period after the accident will be filled by filling the lower drywell with water by the gravity drop pool, and then increasing the height of the entrance of the vent pipe connecting the drywell and the pressure suppression pool (or the water to the pressure suppression pool). It was necessary to fill the pool with water up to the height of the return line, and a large amount of gravity-drop pool water was required.

In Known Example 2, short-term core cooling after LOCA is performed in the pressure storage tank of ECC8, and long-term core cooling after LOCA is achieved by a pressure equalization system that connects the pressure suppression pool and the pressure vessel, as in Known Example 1. Ru. Therefore, in order to maintain the water balance in the containment vessel for a long period of time after the accident, it was necessary to install a large-capacity pressure storage tank or, for a long period after the accident, to inject coolant into the pressure vessel using a dynamic pump. .

[Problem to be solved by the invention]

In all of the above conventional technologies, when considering the long-term water balance in the containment vessel after LOCA, in order to fill the lower dry well with coolant up to the height of the vent pipe, a gravity drop ECC5 pool or a pressure accumulating ECC5 pool is used. It was necessary to increase the amount of water in the tank. For this reason, in Publication Example 1, in particular, in order to install a large capacity pool in the upper part of a building, it was necessary to thicken the structure wall supporting the pool, and there was a problem in that the seismic conditions became stricter.

The purpose of the present invention is to provide an emergency core injection system for a nuclear reactor that minimizes the amount of coolant required to fill the lower dry well by providing two water sources for the pressure equalization system during long-term cooling after a LOCA. It is to provide a water system.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a pressure vessel containing the core of a light water reactor and a containment vessel containing the pressure vessel, and the containment vessel encloses the pressure vessel and the high-temperature/high-pressure primary system piping. An emergency core water injection system for a nuclear reactor that is divided into a dry well and a pressure suppression chamber having a pressure suppression pool at the bottom, and the dry well and the pressure suppression pool are connected by a vent pipe whose lower end is submerged in water, In the event of a short-term abnormality in the reactor, the steam inside the pressure vessel can be released to depressurize the pressure vessel, and emergency facilities such as a gravity drop pool installed in the upper internal space of the containment vessel or a pressure accumulator tank installed outside the containment vessel are installed. In the emergency core water injection system of a nuclear reactor, which cools the reactor core by injecting water into the pressure vessel by the core cooling system, when a reactor abnormality occurs, pool water in the pressure suppression pool and draw water accumulated in the lower part of the dry well over a long period of time are collected. A pressure equalization system is installed that uses both down water as water sources and injects water into the pressure vessel.

Preferably, the pressure equalization system includes a first pressure equalization pipe that connects the pressure suppression pool and the pressure vessel, and a second pressure equalization pipe that branches from the first pressure equalization pipe and opens at the bottom of the dry well. an isolation valve that is closed during normal operation is installed between the connection point of the first pressure equalization pipe with the pressure vessel and the branch point of the second pressure equalization pipe; A check valve is installed between the branch point of the first pressure equalizing pipe and the connection point with the pressure suppression pool and in the second pressure equalizing pipe, respectively.

Preferably, the containment vessel is made of steel, and its wall surface serves as a heat transfer surface for transmitting heat from the pressure suppression pool to the outer peripheral pool in the event of an abnormality in the reactor, and the pressure suppression of the first pressure equalization pipe is preferably The height of the opening in the pool should be near the pool water surface.

Preferably, after detecting a low water level signal in the pressure vessel and a high pressure signal in the dry well and opening a pressure reducing valve that releases steam in the pressure vessel, a low pressure signal in the pressure vessel is detected and the isolation is performed. Control means are provided to open the valve.
A break valve or an electric valve can be used as the isolation valve. Two isolation valves and two check valves may be arranged in parallel to the first and second pressure equalizing pipes.

[Effect]

In the present invention configured as described above, a pressure equalization system is provided that injects water into the pressure vessel using two water sources, the pool water of the pressure suppression pool and the drawdown water at the lower part of the dry well, for a long period of time when there is an abnormality in the reactor. As a result, the drawdown water in the lower drywell can be used directly as a new water source, and there is no need to fill the drawdown water up to the vent pipe height and return it to the pressure suppression pool for use. The amount of coolant required to fill the well can be reduced. Note that drawdown water refers to cooling water that has flowed out from the break and ECC that has leaked from the break.
5 gravity drop pool water or pressure storage tank water.

Furthermore, since decay heat can be removed from the pressure suppression pool to the outer peripheral pool via the containment vessel wall surface, core cooling and containment vessel cooling can be achieved by static means for a long period after LOCA.

Further, by providing a control means that detects a low water level signal of the pressure vessel and a high pressure signal of the dry well to open the pressure reducing valve, and then detects a low pressure signal of the pressure vessel and opens the isolation valve, the LoA After that, in the process of decreasing the pressure in the pressure vessel, the pressure reducing valve is automatically opened, and then the isolation valve of the pressure equalization system is opened.

When the isolation valve of the pressure equalization system is opened and the pressure in the pressure vessel is sufficiently reduced in the long term after LOCA, pool water in the pressure suppression pool and drawdown water in the lower dry well flow into the pressure vessel at head pressure. At this time, the first
Since a check valve is installed in the second pressure equalizing pipe, the water in the pressure vessel will not flow back into the lower dry well or pressure suppression pool, and the pool water in the pressure suppression pool will not flow back into the lower dry well. There is no inflow into the country.

〔Example〕

A first embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

In a boiling water type light water reactor, as shown in FIG. 2, there are a pressure vessel 2 containing a reactor core 1 and a containment vessel 3 containing the pressure vessel 2.
is installed. The containment vessel 3 is divided into a dry well 4 containing the pressure vessel 2 and high temperature/high pressure primary system piping, and a pressure suppression chamber 6 having a pressure suppression pool 5 at the bottom. They are connected by a plurality of vent pipes 7 whose lower ends are submerged in water.

Containment Vessel 3 is made of steel and is subject to a loss of coolant accident (LO
CA), decay heat is removed from the pressure suppression pool 5 to the peripheral pool 8 via the wall surface of the containment vessel 3.

In FIG. 1, the pressure vessel 2 is provided with a pressure reducing valve 9,
A gravity drop pool 10 is installed in the upper space inside the containment vessel 3 as a water source for the gravity drop type emergency core cooling system (ECC8) 11. The pressure in the pressure vessel 2 is rapidly reduced by releasing the steam to escape from the system, and water from the gravity drop pool 10 is injected into the pressure vessel 2 at head pressure to cool the reactor core 1. Gravity drop pool 10 as a water source for ECC3lI
Instead, as shown in FIG. 3, a pressure accumulator tank 12 may be provided outside the containment vessel 3, and water from this pressure accumulator tank 12 may be injected into the pressure vessel 2 to cool the reactor core 1. The water injected into the gravity drop pool 11 or the pressure storage tank 12, which operates for a short period of time after LOCA, flows out into the dry well 4 through the fracture opening (not shown) after cooling the core 1, and flows into the dry well 4 through the fracture opening (not shown). As shown in the figure, the lower space of the dry well 4 is filled with water, and the lower half of the pressure vessel 2 is submerged in water.

In addition, a pressure equalization system 13 is installed in the pressure vessel 2, which uses both the pool water of the pressure suppression pool 5 and the drawdown water accumulated in the lower part of the dry well 4 as water sources, and this pressure equalization system 13 is used for a long period of time after LOCA. The pressure system 13 injects pool water from the pressure suppression pool 5 and/or drawdown water 17 from the lower part of the dry well 4 into the pressure vessel 2 . The pressure equalization system 13 includes a first pressure equalization pipe 14a whose one end is connected to the pressure vessel 2 and whose other end opens to the pressure suppression pool 5, and which branches from the first pressure equalization pipe 14a and connects to the lower part of the dry well 4. Explosion as an isolation valve disposed between the second pressure equalizing pipe 14b that opens to the second pressure equalizing pipe 14b, the connection point of the first pressure equalizing pipe 14a with the pressure vessel 2, and the branching point of the second pressure equalizing pipe 14b. Valve 15 and pressure equalization piping 14a, 1
4b, and a check valve 16 installed at each of the valves 4b.

The connection height between the pressure vessel 2 and the first pressure equalization piping 16a (hereinafter abbreviated as "pressure vessel piping connection height") is set so that the reactor core can be maintained with sufficient margin for a long period after LOCA.
It is installed about 50 to 150 cm above the top of the reactor core, preferably about 1 m. The driving force for injecting pool water into the pressure suppression pool 5 is the difference between the outlet height of the vent pipe 7 and the pressure vessel piping connection height, as will be described later. The height should be about 50 to 150 cm, preferably 70 cm or higher. In addition, the outlet height of the vent pipe 7 is 100 cm to 2 cm higher than the height of the reactor core 1.
00 cm higher. Note that the outlet height of the vent pipe here refers to the height of the opening to the pressure suppression pool at the lower end of the vent pipe 7, and when the vent pipe 7 has a plurality of exits each having a different height, This is the height of the highest exit among those exits.

Further, the driving force for injecting the drawdown water 17 into the dry well 4 is the difference between the water level of the drawdown water 17 and the pressure vessel piping connection height, as will be described later.

Here, the opening height of the second pressure equalizing pipe 14b at the bottom of the dry well 4 is set to be approximately the same level as the connection height with the pressure vessel 2, and air accumulates in the second pressure equalizing pipe 14b, causing the drive In order not to reduce the force, the second pressure equalizing pipe 14
The wiring of b is kept to a minimum including the horizontal wiring, and the check valve 16 is installed in the horizontal wiring part. In FIG. 1, only a portion A surrounded by a chain line is shown in a plan view for convenience of illustration. The same applies to other figures. In addition, the amount of water in the weight drop pool 10 or pressure accumulation tank 11 of ECC8 is L
The drawdown water level in the lower dry well is set in advance so as to be equal to or higher than the pressure vessel piping connection height, that is, the height of the second pressure equalizing piping 14b for a long period after OCA.

In addition, in this embodiment, since the wall surface of the containment vessel 3 after LOCA functions as a heat transfer surface that transfers the heat of the pressure suppression pool 5 to the outer peripheral pool 8, a large amount of water from the pressure suppression pool 5 is used to lower the water level. I can't let you. Therefore, the opening height of the first pressure equalizing pipe 14a is set to be, for example, about 50 cm lower than the initial water level of the pressure suppression pool 5, so that the water level does not fall below that level.

After LOCA, the pressure in pressure vessel 2 will decrease to dry well 4 for a long time.
When the pressure decreases to approximately the same level as the pressure, the pressure equalization system 13 is activated, and the water in the pressure suppression pool 5 and the drawdown water 17 at the lower part of the dry well 4 flow into the pressure vessel 2, as shown in FIG. At this time, the driving force for injecting pool water into the pressure suppression pool 5 and the driving force for injecting drawdown water 17 into the dry well 4 are each expressed by the following equations.

■Driving force ΔP of pressure suppression pool water.

ΔP+=PNtP* =(Pww+(Hv+HNV)'γ)-P.

YoHNV・γ... (1) Because Pww+Hv 'γ#PR-(2) ■ Driving force of drawdown water at the bottom of the dry well ΔΔP2=PNE PR = (pH, w+Ho ・γ)−plI≠H,・γ
...(3) Here, PR: Pressure of pressure vessel Pow Pressure of dry well Pww: Pressure of pressure suppression chamber Hv; Vent pipe water immersion depth HNV: Vent pipe outlet height and pressure vessel piping connection height Difference HD Difference between nitro-down water level and pressure vessel piping connection height γ: Density of water Therefore, from equation (1), the driving force ΔP1 for water injection into the pressure suppression pool 5 is the difference between the outlet height of the vent pipe 7 and the pressure vessel pipe connection height. The head pressure corresponds to the difference between the connection height of the pressure equalizing pipe 14a and the pressure equalizing pipe 14a, and from equation (3), the injection driving force of the drawdown water 17 at the bottom of the dry well 4 is equal to the equalizing pressure between the drawdown water level and the pressure vessel 2. The head pressure corresponds to the difference in connection height of the pipes 14b.

Next, a control system for the pressure equalization system 13 will be explained with reference to FIGS. 5 and 6.

In FIG. 5, a water level gauge 19 that detects the water level LR in the pressure vessel 2 as part of the control system, and a pressure P in the dry well 4 are shown.
A pressure gauge 20 that detects D and a pressure P in the pressure vessel 2
A pressure gauge 21 is provided to detect . Water level gauge 19
, the detection signals of the pressure gauges 20 and 21 are sent to the controller 22, where the pressure reducing valve 9 is activated according to the operating logic shown in FIG.
and starts the pressure equalization system 13.

In other words, a LOCA event occurs and the water level L in the pressure vessel 2
R low signal and dry well 4 pressure P. When a high signal is detected, the pressure reducing valve 9 is opened, and as a result, the pressures P and l in the pressure vessel 2 rapidly decrease and approach the dry well 4 pressure. The explosion valve 15 is opened.

After opening the blast valve 15, the coolant is automatically injected if the injection conditions of equations (1) and (3) are satisfied. While the above conditions are not met, the check valve 16 is installed in the pressure equalization system 13, so reactor water will not flow out.

According to this embodiment configured as above, after LOCA,
In the process of reducing the pressure in the pressure vessel, the blast valve 25 is opened, and the water in the pressure suppression pool 5 and the drawdown water 17 at the bottom of the dry well 4 are injected into the pressure vessel 2.
The core 1 can be cooled for a long period of time after CA.

Furthermore, since water is injected using both the water in the pressure suppression pool 5 and the drawdown water 17 at the lower part of the dry well 4 as water sources, the pressure equalizing plumber 4a can be applied to the pressure vessel 2 without filling the entire lower part of the dry well 4 with water.

Water can be injected by filling it up to a level slightly (~1 m) higher than the connection height of the reactor 14b, and the reactor core 1 can be kept submerged for a long period of time after LOCA. Therefore, ECC8 gravity fall pool 1
0 water volume or the water volume of the ECC5 pressure storage tank 12 can be reduced, there is no need to secure heavy water in the upper part of the building, and the seismic design can be relaxed.

In addition, the wall surface of the containment vessel 3 after LOCA functions as a heat transfer surface that transfers the heat of the pressure suppression pool 5 to the outer peripheral pool 8, but the opening height of the pressure equalization pipe 14a is slightly lower than the initial water level of the pressure suppression pool. Since the water level is kept low and the water level does not fall below that level, static containment vessel cooling via the wall surface of the containment vessel 3 and static core cooling by the above-mentioned pressure equalization system 13 can be achieved over a long period of time. I can do it.

In addition, at this time, if the tip opening of the pressure equalizing pipe 14a on the pressure suppression pool 5 side is exposed to the gas phase, the second pressure equalizing pipe 14a is always connected to the lower part of the dry well 4 due to the water balance in the containment vessel 3. The pressure vessel 2 is covered with drawdown water 17 of
Since the reactor core 1 can be injected with water, the reactor core 1 can be cooled without fail.

A second embodiment of the present invention will be described with reference to FIG.

In the first embodiment shown in FIG. 1, an explosion valve 15 was installed as an isolation valve in the pressure equalization pipe 14a, but in this embodiment, the pressure equalization system 1
An electric valve 23 that is closed during normal operation is installed in the pressure equalizing pipe 14a at 3A instead of the blast valve. Electrically operated valve 22 is also opened using the same operating logic as shown in FIG.

According to this embodiment, since the electric valve 22 is used, there is an effect that the reliability of the isolation valve can be easily confirmed by a periodic test.

In addition, operation and management become easier.

A third embodiment of the present invention will be described with reference to FIG.

In this embodiment, in the first embodiment shown in FIG.
Two blast valves 15 and two check valves 16 are installed in parallel.

It is necessary to assume that valves that are closed during normal operation and are required to open in the event of a LOCA event fail for some reason and cannot be expected to operate as expected; however, according to this example, any dynamic It is possible to inject coolant into the pressure vessel 2 even in the case of a single equipment failure.

〔Effect of the invention〕

According to the present invention, water can be injected into the pressure vessel 2 using two water sources, the drawdown water of the pressure suppression pool and the dry well, so that the following effects can be obtained.

■Gravity drop ECC8 pool water volume can be reduced.

■Earthquake resistance conditions can be eased by reducing the weight of the upper part of the building.

■By reducing the weight of the upper part of the building, the thickness of the building walls can be reduced.

Additionally, adding a water source can be handled with a minor addition of equipment, such as adding a short piece of piping and a check valve in the middle of the existing piping route.

Furthermore, since decay heat can be removed from the pressure suppression pool to the outer peripheral pool via the containment vessel wall surface, core cooling and containment vessel cooling can be achieved by static means for a long period after LOCA.

By adopting an electric valve, it is possible to improve economic efficiency, maintainability, and reliability.

It is possible to achieve a predetermined function even assuming a single failure of any dynamic equipment.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an emergency core water injection system according to a first embodiment of the present invention, FIG. 2 is a sectional view showing the overall configuration of a light water reactor, and FIG. Fig. 4 is a schematic diagram of an emergency core water injection system as a modified example.
FIG. 5 is a diagram showing the control system of the emergency core water injection system, and FIG. 6 is a diagram showing the control system of the emergency core water injection system.
The figure is a diagram showing the activation logic of the pressure equalization system by the control system, FIG. 7 is a schematic diagram of the emergency core water injection system according to the second embodiment of the present invention, and FIG. FIG. 3 is a schematic diagram of an emergency core water injection system according to the third embodiment. Explanation of symbols 1... Core 2... Pressure vessel 3... Containment vessel 4... Dry well 5... Pressure suppression pool 6... Pressure suppression chamber 7... Vent pipe 8... Outer pool 9...Reducing valve 10...Gravity drop pool 11...Emergency core cooling system (E CC5) 12...
- Pressure storage tank 13...Pressure equalization system 14a...First pressure equalization piping 14b...Second pressure equalization piping 15...Blast valve (isolation valve) 16...Check valve 17...・Drawdown water 22...Controller (control means) Applicant: Hitachi, Ltd. Representative Patent Attorney Yuzuru Kasuga Figure 4 Figure 6 Figure 7 Figure 8

Claims (7)

[Claims] (1) A pressure vessel containing the core of a light water reactor and a containment vessel containing the pressure vessel are provided, and the containment vessel has a dry well that envelops the pressure vessel and the high temperature/high pressure primary system piping, and a pressure suppressor in the lower part. The dry well and the pressure suppression pool are connected to each other by a vent pipe whose lower end is submerged in water.It is an emergency core water injection system for the reactor, and is used for short-term use in the event of a reactor abnormality. The steam inside the pressure vessel is released to depressurize the pressure vessel, and water is injected into the pressure vessel using an emergency core cooling system equipped with a gravity drop pool installed in the upper internal space of the containment vessel or a pressure accumulator tank installed outside the containment vessel. In the emergency core water injection system of a nuclear reactor, which cools the reactor core by using both the pool water of the pressure suppression pool and the drawdown water accumulated in the lower part of the dry well for a long period of time in the event of a reactor abnormality, the water source is An emergency core water injection system for a nuclear reactor characterized by installing a pressure equalization system that injects water into a pressure vessel. (2) In the emergency core water injection system for a nuclear reactor according to claim 1, the pressure equalization system includes a first pressure equalization pipe connecting the pressure suppression pool and the pressure vessel, and a branch from the first pressure equalization pipe. and a second pressure equalizing pipe that opens at the bottom of the dry well, and between a connection point of the first pressure equalizing pipe with the pressure vessel and a branch point of the second pressure equalizing pipe. An isolation valve that is closed during normal operation is installed, and a check valve is installed between the branch point of the first pressure equalization pipe and the connection point with the pressure suppression pool and between the second pressure equalization pipe, respectively. An emergency core water injection system for a nuclear reactor, which is characterized by having been installed. (3) In the emergency core water injection system for a nuclear reactor according to claim 2, the containment vessel is made of steel, and the wall surface functions as a heat transfer surface to transfer heat from the pressure suppression pool to the outer peripheral pool in the event of an abnormality in the reactor. An emergency core water injection system for a nuclear reactor, characterized in that the opening height of the first pressure equalizing pipe in the pressure suppression pool is in the pool water and near the pool water surface. (4) In the emergency core water injection system for a nuclear reactor according to claim 2, after detecting a low water level signal in the pressure vessel and a high pressure signal in the dry well and opening a pressure reducing valve that releases steam in the pressure vessel. An emergency core water injection system for a nuclear reactor, characterized in that the emergency core water injection system for a nuclear reactor is provided with a control means for detecting a low pressure signal of the pressure vessel and opening the isolation valve. (5) The emergency core water injection system for a nuclear reactor according to claim 2, wherein a blast valve or an electric valve is used as the isolation valve. (6) The emergency core water injection system for a nuclear reactor according to claim 2, characterized in that two isolation valves and two check valves are each arranged in parallel to the first and second pressure equalizing pipes. Emergency core water injection system for a nuclear reactor. (7) A pressure vessel containing the core of a light water reactor and a containment vessel containing the pressure vessel are provided, and the containment vessel includes a dry well that encloses the pressure vessel and the high temperature/high pressure primary system piping, and a pressure suppression vessel in the lower part. The dry well and the pressure suppression pool are connected to each other by a vent pipe whose lower end is submerged in water.It is an emergency core water injection system for the reactor, and is used for short-term use in the event of a reactor abnormality. The steam inside the pressure vessel is released to depressurize the pressure vessel, and water is injected into the pressure vessel using an emergency core cooling system equipped with a gravity drop pool installed in the upper internal space of the containment vessel or a pressure accumulator tank installed outside the containment vessel. In the emergency core water injection system of a nuclear reactor, which cools the reactor core, a pressure equalization system is installed that injects water into the pressure vessel using drawdown water that has accumulated in the lower part of the dry well over a long period of time as a water source in the event of a reactor abnormality. An emergency core water injection system for a nuclear reactor that is characterized by: