JPS62182697A - Nuclear reactor cooling system - 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] [Industrial Application Field] The present invention relates to a nuclear couplant, and particularly to a core cooling system suitable for removing residual heat from a reactor core and cooling the core during an accident or abnormal transient change. Regarding.

[Conventional technology]

Figure 2 shows a pressure accumulator system used in a conventional pressurized water reactor (PWR). This system automatically injects cooling water and replenishes coolant when the pressure of the primary cooling system drops below the holding pressure of the pressure storage tank 21 in the event of an accident. The air storage tank 21 is filled with cooling water and pressurized nitrogen for injection, and does not require external power for injection.

This pressure accumulator system plays an important role in cooling the reactor core, especially immediately after blowdown is completed in the event of a major rupture of the secondary coolant pipe.

However, conventional PWR pressure accumulators inject cooling water into the core in the event of a loss of coolant accident, and do not remove decay heat from the core during abnormal transient changes.

Further, since it is connected to the primary coolant low temperature side pipe 22, the pressure accumulator connected to the broken pipe is useless in case of a loss of coolant accident. Therefore, it was necessary for each PWH primary coolant system.

FIG. 3 shows an emergency condenser 31 used in a conventional boiling water reactor (BWR). The emergency condenser 31 removes the decay heat of the reactor when the main condenser cannot be used during an abnormal transient change such as a turbine trip. The emergency condenser 31 has a condenser tank filled with cooling water and a thin tube through which reactor steam passes through the cooling water, and is connected to the reactor pressure vessel 1 . The emergency condenser 31 operates due to high reactor pressure, and the steam in the steam pipe 32 and the drain pipe 3
The structure is such that the reactor core is cooled by natural circulation based on the difference in head of condensate within the reactor, without the need for dynamic equipment such as pumps.

However, the emergency condenser 31 used in conventional BWRs did not have the ability to inject water in the event of a loss of coolant accident.

The design pressure of the tank was also lowered by opening the shell side to the atmosphere.

In addition, as a publicly known side of this kind, Japanese Patent Application Laid-Open No. 57-69289
There is something described in the publication.

[Problem that the invention seeks to solve]

Currently, regarding the safety system of nuclear reactors, in order to improve reliability, improve economic efficiency, or improve inherent safety, consideration is being given to ensuring the safety of the reactor core using natural forces without using dynamic equipment. has been done. Furthermore, from the perspective of improving economic efficiency, it was desired that the same equipment would be able to perform the decay heat removal function and water injection function of a nuclear reactor.

The purpose of the present invention is to ensure the safety of a reactor core using the power of nature without using dynamic equipment, and to achieve the decay heat removal and water injection functions of a nuclear reactor with the same equipment.

[Means for solving problems]

In order to achieve the above object, the present invention provides a tank in a light water nuclear reactor, which has a double pipe structure consisting of a body and a pipe section that are normally filled with water and is installed at a higher position than the reactor pressure vessel; a first steam pipe connecting the tank body side gas phase part and the reactor pressure vessel gas phase part;

A second steam pipe that connects the upper part of the tank pipe side and the reactor pressure vessel gas phase part, a water injection pipe that connects the tank body side liquid phase part and the reactor pressure vessel liquid phase part, and a water injection pipe that connects the tank pipe side lower part and the pressure vessel part. It consists of piping that connects the liquid phase part of the container, and is designed to have an emergency condensing function in the event of abnormal plant transients and an emergency cooling function in the event of an accident.

[Effect]

The present invention is characterized in that in the event of an accident, coolant is injected into the reactor pressure vessel using steam within the reactor pressure vessel.

At this time, an operating logic is configured such that the design pressure does not increase when reactor steam is injected into the M side. Furthermore, in the event of an abnormal transient change, the stored coolant is used to function as an emergency condenser 1. That is, in one aspect of the present invention, a tank with a double pipe structure is provided at a higher position than the reactor pressure vessel, and the shell side of the tank is normally filled with water.

In the event of an accident, reactor steam is injected into the tank body side gas phase part and 11th side coolant is injected into the reactor pressure vessel based on pressure and water level signals. On the other hand, during abnormal transient changes, heat is removed from the reactor core by passing reactor steam through the tank pipe side and exchanging heat with the shell side coolant.

〔Example〕

FIG. 1 shows an overview of the present invention.

The present invention relates to a tank 2 which is normally placed at a higher position than a reactor pressure vessel 1 and is filled with water, a steam pipe connecting a gas phase part of the tank 2 to a steam phase part of the reactor pressure vessel, and It consists of a water injection pipe 6 that connects the liquid phase part of the tank 2 to the liquid phase part of the reactor pressure vessel 1. A thin tube for heat transfer passes through the tank 1, and the tank is divided into a tube side 3 and a +m side 4.

A steam pipe 5 and a water injection pipe 6 that connect the pressure vessel 1 and the tank are separated in the middle and connected to the tank body side 4 and the pipe side 3, respectively. Further, a steam control valve 7 is provided in the middle of the pipe connecting the steam pipe 5 and the tank pipe side 3, a steam injection valve 8 is provided in the middle of the pipe connecting the steam pipe 5 and the tank body side 4, and the water injection pipe 6
A condensate valve 9 is installed in the pipe connecting the tank pipe side 3 and a coolant injection valve 1 is installed in the pipe connecting the water injection pipe 6 and the tank body side 4.
0 is set.

Due to this structure, in the event of an accident, the reactor pressure vessel 1 → steam pipe 5
→ Steam injection valve 8 → Tank body side 4 → Coolant injection valve 10 → Water injection pipe 6 → Reactor pressure vessel 1 constitute a closed circuit.

On the other hand, during an abnormal transient change, a closed circuit is formed by the reactor pressure vessel 1 - the steam pipe 5 - the steam control valve 7 - the tank pipe side 3 - the condensate valve 9 - the water injection pipe 6 - the reactor pressure vessel 1.

Further, during normal operation, the condensate valve 9 and the coolant injection valve 10 are closed.

On the other hand, the steam control valve 7 is open and the steam injection valve 8 is closed.

Therefore, the area from the reactor pressure vessel 1 to the middle of the thin tube in the tank is filled with steam, and the area from the middle of the thin tube to the condensate valve 9 is filled with water to maintain an equilibrium state.

[During abnormal transient changes]

Figure 4 shows the operating method during abnormal transient changes.

Turbine bypass valve fails to open during turbine trip,
Alternatively, when the main condenser cannot be used due to a drop in vacuum in the main condenser, etc., the present invention allows the decay heat of the reactor to be removed.

In such a case, the condensate valve 9 connecting the water injection pipe 6 and the tank pipe side is opened.

When this valve is opened, the core is cooled by natural circulation due to the head difference between the steam in the steam pipe and the condensate in water injection pipe -6.

That is, the steam in the reactor pressure vessel 1 returns to the reactor through the steam pipe 5. The cooling water in the tank absorbs the heat of the primary system and boils, and the generated steam passes through the vent valve 11 and is released into the atmosphere.

[At the time of accident]

Figure 5 shows the driving method in the event of an accident.

In the event of an accident such as a pipe breakage, the present invention functions as a low-pressure emergency water injection system.

When the reactor pressure becomes low to a certain extent, the vent valve 11 that opens the tank to the atmosphere is closed, the steam control valve 7 that connects the steam pipe 5 and the pipe side is left open, and the steam pipe 5 is connected to the shell side. The steam injection valve 8 and the coolant injection valve 9 connecting the water injection pipe 6 and the shell side are opened.

As a result, the steam in the reactor pressure vessel flows into the tank shell side 4, and when the pressures in the reactor pressure vessel and the tank shell side 4 become equal, the cooling water in the tank shell side 4 falls due to gravity, and the reactor pressure vessel Water is injected into 1.

FIG. 6 shows a schematic diagram of the BWR-5 and ABWR reactors.

The operating characteristics during LOCA will be explained based on FIG. 6. Recirculation piping (PLR) is installed.

Therefore, a rupture at both ends at this location is assumed to be the worst accident event, and in this case, the coolant inside the reactor will flow out through the PLR piping and the reactor core will be exposed.

For this reason, injecting water to the outside of the shroud in conventional BWRs could not be expected to have a cooling effect in the event of an accident.

On the other hand, in the ABWR plant on the right side of the figure, there is no large-diameter piping below the pressure vessel.

Therefore, breakage of small and medium-sized pipes above the reactor core has been determined as a design basis accident, and in the event of an accident, the flow rate of coolant leaking inside the reactor will be suppressed, and the reactor water level will be maintained high even in the event of a LOCA.

For this reason, injecting coolant to the outside of the shroud is
It has a great effect on flooding the reactor core and cooling the reactor core.

Next, the effects of the present invention will be evaluated separately for both abnormal transient changes and accidents.

[During abnormal transient changes]

Figure 7 shows reactor pressure and reactor water level changes during abnormal transient changes.

In this evaluation, it is assumed that the turbine bypass valve fails to close when the turbine trips.

Although the reactor scrams at time 0 seconds, if there is no residual heat removal system in the reactor core, it is thought that the reactor pressure will gradually increase.

However, due to the condensation function of the present invention, the reactor steam is condensed and the reactor pressure gradually decreases.

Additionally, the reactor water level hardly changes during this period.

[At the time of accident]

Figure 8 shows changes in reactor pressure and reactor water level at the time of the accident.

This evaluation is considered to be the most severe in ABWR.
'This assumes that the C3 pipe is damaged.

After the accident, the reactor pressure gradually rose due to the closure of the main steam isolation valve, but started to drop due to the operation of the automatic pressure reduction system.During this period, the reactor water level did not fall below the top of the effective fuel length, but When the automatic depressurization system operates to complete the depressurized boiling, the reactor water level continues to gradually decrease. However, when the reactor pressure reaches the set pressure of the cooling system of the present invention, water injection begins by gravity falling from the tank to the reactor core, and the reactor core is not exposed.

In this way, the system for removing decay heat during abnormal transient changes and the system for injecting water into the reactor core in the event of an accident, which were installed independently in conventional equipment, can now be combined into one piece of equipment. Because it is possible, spatially as well. There is also a big cost advantage.

In addition, when viewed as a water injection system in the event of an accident, the present invention is a gravity-drop type water injection system that uses steam in the reactor pressure vessel, so compared to conventional safety systems, it has fewer moving components and is highly reliable. safety and inherent safety.

〔Effect of the invention〕

With the present invention, the system for removing decay heat during abnormal transient changes and the system for injecting water into the reactor core in the event of an accident, which were installed independently in conventional equipment, can be combined into one piece of equipment. Yes.

There are significant advantages in terms of space and cost.

In addition, when viewed as a water injection system in the event of an accident, the present invention is a gravity-drop type water injection system that uses steam in the reactor pressure vessel, so compared to conventional safety systems, it has fewer moving components and is highly reliable. It has the advantage of having safety and inherent safety.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing an embodiment of the present invention, Fig. 2 is a system diagram showing a conventional PWR pressure accumulation system, and Fig. 3 is a system diagram showing a conventional PWR pressure accumulation system.
System diagram showing WR's emergency condenser, Figures 4 and 5
The figures are diagrams explaining the present invention in detail. Figure 4 is a diagram showing operation during abnormal transients, Figure 5 is a diagram showing operation during an accident, and Figure 6 is a diagram showing a comparison between ABWR and BWR. Sectional view shown, No. 7
The figure is a diagram explaining the evaluation at the time of abnormal transient change of the present invention,
FIG. 8 is a diagram showing JArv7 evaluation of the present invention at the time of an accident. 1... Reactor pressure vessel, 2... Tank, 3... Tank pipe side, 4... Tank body side, 5 River steam pipe, 6... Water injection piping, 7... Steam control valve, 8. Steam injection valve, 9.
...Condensate valve. 10... Coolant injection valve, 11... Vent valve, 21.
... Pressure storage tank, 22 ... Primary coolant low temperature side piping, 3
1... Emergency condenser, 32... Steam pipe, 33...
drain pipe.

Claims (1)

[Scope of Claims] 1. In a light water nuclear reactor, a tank having a double pipe structure consisting of a body and a tube that is normally filled with water and installed at a higher position than the reactor pressure vessel, and the tank A first steam pipe that connects the shell side gas phase part and the reactor pressure vessel vapor phase part, a second steam pipe that connects the upper part of the tank pipe side and the reactor pressure vessel gas phase part, and a liquid phase part of the tank shell side. It consists of a water injection pipe that connects the reactor pressure vessel liquid phase section to the reactor pressure vessel liquid phase section, and a water injection pipe that connects the lower part of the tank pipe side and the pressure vessel liquid phase section.It has an emergency condensation function during abnormal plant transients and an emergency condensation pipe in the event of an accident. A nuclear reactor cooling system characterized by having an emergency cooling function. 2. In claim 1, in the event of an accident, steam from the reactor pressure vessel is injected into the tank body side through the first steam pipe, and the pressures in the tank and the reactor pressure vessel are equalized before free falling. A nuclear reactor cooling system characterized in that water in the tank is injected into a reactor pressure vessel. 3. In claim 1, at the time of an accident, reactor steam is injected into the tank based on both the preset reactor pressure low and reactor water level low signals, and the cooling water in the tank is supplied to the reactor pressure. A nuclear reactor cooling system characterized in that the design pressure of a tank is reduced by injecting water into the container. 4. In claim 1 or 2, when there is an abnormal transient change in the plant, the gas phase part on the tank body side is opened to the atmosphere, and the steam in the reactor pressure vessel is passed through the tank pipe side. A nuclear reactor cooling system characterized by exchanging heat with the coolant in the tank and condensing the reactor steam to remove heat from the reactor core.