JPS60259995A - 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] [Technical Field of the Invention] This invention relates to an emergency core cooling system for water-cooled light water reactors such as boiling water reactors, pressurized water reactors, and natural circulation reactors. In particular, the present invention relates to an emergency core cooling system that actively replenishes coolant in the event of a loss of coolant accident such as a rupture of secondary system piping.

[Technical background of the invention and its problems]

Generally, light water reactors use water as a coolant and are broadly divided into boiling water reactors, pressurized water reactors, natural circulation reactors, etc. Among these, the natural circulation reactor is constructed as shown in Fig. 4, in which a cylindrical shroud 2 is disposed concentrically within a reactor pressure vessel 1, and nuclear fuel is installed within this shroud 2. A reactor core 3 is formed. A riser section 4 is formed above the reactor core 3, and a control rod drive mechanism 5 moves control rods into and out of the reactor core 3 via the riser section 4, thereby adjusting the reactor power.

On the other hand, a downcomer section 6 having an annular cross section is defined between the inner peripheral wall surface of the reactor pressure vessel 1 and the shroud 2, and a plurality of heat exchangers 7 are provided above the downcomer section 6.

Therefore, the coolant filled in the reactor pressure vessel 1 is
The IC steam is heated by the heat generated in the reactor core 3 and rises through the riser section 4 while boiling, and the IC steam generated here is heat exchanged in the heat exchanger 7, condensed, and falls into the downcomer section 6.

The condensed water that has fallen into the downcomer section 6 generates a driving force due to the density difference between the coolant in this section and the bath coolant in the reactor core 3 and riser section 4, and as a result, the cooling inside the reactor pressure vessel 1 is reduced. The wood is allowed to circulate naturally. Due to this natural circulation, the coolant in the downcomer section 6 descends and is guided to the lower part of the reactor core, and then flows into the reactor core 3 from the lower part of the reactor core.

In such reactors, in the event of a loss of coolant accident due to a rupture in the primary system piping, the emergency core cooling system is activated to sufficiently cool the reactor core and maintain the integrity of the nuclear fuel rods. ing. In the conventional emergency core cooling system 8, as shown in FIG. 5, a coolant water storage tank 9 is installed at a higher place than the reactor pressure vessel 1. It is supplied into the reactor pressure vessel 1 through the core cooling system piping 9a, and even in the event of a loss of coolant accident,
It is configured to maintain the core flooding condition.

However, since the upper end of the coolant storage tank 9 is open, it is not always possible to replenish the coolant sufficiently just by supplying the coolant by gravity, and the pressure inside the reactor pressure vessel 1 increases. It was not possible to supply coolant until it was sufficiently low.

In addition, the flow rate of coolant after the start of coolant supply gradually decreases because the pressure in the reactor pressure vessel 1 overwhelms the pressure in the water storage tank 9, and there is a risk that the coolant will not be supplied quickly and sufficiently. was there.

[Purpose of the invention]

This invention was made in consideration of the above-mentioned circumstances, and it is designed to ensure that, in the event of a loss of coolant accident, coolant is sufficiently and quickly replenished into the reactor pressure vessel regardless of the pressure inside the reactor pressure vessel. The purpose is to provide an emergency core cooling system that can improve the reliability and safety of a nuclear reactor.

C invention f,? Summary] In order to achieve the above-mentioned object, this invention installs a non-rich core cold W system water storage tank at a higher location than the reactor pressure vessel, and also connects the water storage tank and the reactor pressure vessel. An emergency reactor core that is connected by water injection piping equipped with a water injection valve, and in the event of a reactor loss of coolant accident, the water injection valve is opened and the coolant in the water storage tank is replenished into the reactor pressure vessel by the action of gravity. , in the cold JI equipment, the water storage tank is configured as a closed pressure vessel, and is communicated with the reactor pressure vessel via a pressure equalization pipe, so that the water storage tank is always maintained at approximately the same pressure as the inside of the reactor pressure vessel. It was designed to be kept.

(Embodiment of the Invention) Hereinafter, an embodiment of the emergency core cooling system according to the present invention will be described with reference to the accompanying drawings.

In FIG. 1, reference numeral 1o indicates a reactor pressure vessel of an eaves water type nuclear reactor such as a boiling water type reactor or a natural circulation type reactor, and an emergency core cooling system 11 is installed in this reactor pressure vessel 10. It will be done. The emergency core cooling system 11 is a reactor pressure vessel 10
It has a coolant water storage tank 12 installed at a higher location, and a water injection pipe 13 as an emergency core cooling system pipe is connected to the bottom of this water storage tank 12. A water injection valve 14 is provided in the middle of the water injection distribution @ 13, and the other end is connected to the lower side wall of the reactor pressure vessel 10, so that the water storage tank 12 and the reactor pressure vessel 10 are maintained in communication with each other.

The water injection pipe 13 is connected to the reactor pressure vessel 10 from the water storage tank 12.
It is arranged continuously downward or partially horizontally.

On the other hand, the water storage tank 12 consists of a sealed pressure vessel,
The top of the tank is connected to the upper side wall of the reactor pressure vessel 10 via a pressure equalization pipe 15. The pressure equalizing pipe 15 has a riser pipe 15a extending upward from the top of the tank, and a fall pipe 15b continuing from the upper end of the riser pipe 15a.
The other end of 5b is connected to the upper side wall of the reactor pressure vessel 10 at a position above the normal water level. With this connection, the pressure inside the water storage tank 12 is maintained at approximately the same pressure as the pressure horn inside the reactor pressure vessel 10.

Next, the operation of the emergency core cooling system will be explained.

During normal reactor operation, the water injection pipe 13, water storage tank 12, and riser pipe 15a of the emergency core cooling system 11 are filled with cooling water, and the water storage tank 12 and the reactor pressure container 10 are filled with the pressure equalization pipe 15. They are communicated by a rising pipe 15a and a falling pipe 15b, and are maintained at approximately the same pressure. At this time, the coolant in the reactor pressure vessel 10 reaches a high temperature due to heat generation in the reactor core (not shown), and the generated steam has a saturation temperature of its pressure.

On the other hand, since the temperature of the water storage tank 12 is equal to the temperature around the tank, the steam in the riser pipe 15a and the fall pipe 15b is cooled and slightly condensed. Heat transfer is largely prevented. Therefore, although the water surface of the riser pipe 15a is close to the saturation temperature, the water temperature in the water storage tank 12 is maintained at a sufficiently low temperature that is approximately equal to the ambient temperature.

Further, during operation of the nuclear reactor, steam condensed water gradually accumulates in the riser pipe 15a, so the water level in the riser pipe 15a gradually rises and reaches the upper end. Since the condensed water thereafter is returned into the reactor pressure vessel 10 from the down pipe 15b, the water surface level is maintained at the upper end position of the rise pipe 15a.

If the primary system piping or the like breaks for some reason and a coolant loss accident occurs, the coolant loss accident is detected and the water injection valve 14 is immediately opened.

When the water injection valve 14 is opened, the pressure in the water storage tank 12 and the reactor pressure vessel 10 is uniform, so the water in the water storage tank 12 immediately flows into the reactor pressure vessel 10 due to gravity based on the water head difference. I am forced to do it.

Therefore, the amount of coolant supplied after the primary system piping is ruptured is stably replenished into the reactor pressure vessel 10, as shown by the solid line coolant supply curve A in FIG. 7J′, that is,
By configuring the emergency core cooling system 11 as shown in FIG. 1, a nearly constant flow of coolant is always maintained regardless of pressure changes in the reactor pressure vessel 10, which is indicated by a dashed line B. is allowed to stably flow into the reactor pressure vessel 10. The coolant supply curve for a conventional nuclear reactor is as shown by the broken line C, and the supply of coolant was not started until the pressure within the reactor pressure vessel 10 was sufficiently lowered.

Furthermore, by configuring the emergency core cooling system 11 as shown in FIG. Stable and smooth supply. For this reason,
The drop in the reactor water level in the reactor pressure vessel 10 can be kept to a minimum as shown by the solid line in FIG. In the conventional reactor plan 1-, the reactor water level decreased as shown by the dotted line E, and there was a risk that the reactor core (the top of the core is represented by the dashed line F) would be exposed. However, in the present invention, since the drop in the reactor water level in the reactor pressure vessel 10 can be suppressed to a minimum, the core can be cooled effectively, and the time required for recovering the reactor water level can also be reduced. be shortened.

In one embodiment of the present invention, an example in which the emergency core cooling system is applied to a boiling water reactor or a natural circulation reactor has been described, but this cooling system can also be applied to a pressurized wooden reactor. Can be applied.

〔Effect of the invention〕

As described above, in the emergency core cooling system according to the present invention, the water storage tank is configured as a closed pressure vessel, the water storage tank is connected to the reactor pressure vessel via a pressure equalizing pipe, and the water storage tank is connected to the reactor pressure vessel. Since the pressure is maintained at almost the same level as inside the pressure vessel, in the event of a reactor loss of coolant accident, the cooling water in the water storage tank can be stably and smoothly supplied by gravity, regardless of the pressure inside the reactor pressure vessel. It can be replenished into the reactor pressure vessel, and the drop in the reactor water level in the reactor pressure vessel can be kept to a minimum.

Therefore, the core of the nuclear reactor can be actively cooled and overheating of the core can be prevented in advance and reliably.

Further, in the event of a reactor loss of coolant accident, a large amount of coolant in the water storage tank can be quickly and smoothly supplied into the reactor pressure vessel, thereby reducing the time required to recover the reactor water level.

Furthermore, since no power such as a pump is required to supply the coolant in the water storage tank, reliability is high and the safety of the nuclear reactor can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the emergency core cooling system according to the present invention, FIG. 2 is a graph showing changes in the amount of coolant supplied from a water storage tank during a loss of coolant accident in a nuclear reactor, and FIG. Figure 4 is a graph showing changes in reactor water level in the reactor pressure vessel during a reactor loss of coolant accident, Figure 4 is a vertical cross-sectional view showing a conventional natural circulation reactor as a light water reactor, Figure 5 The figure shows a conventional emergency core cooling system. DESCRIPTION OF SYMBOLS 10... Reactor pressure vessel, 11... Emergency core cooling system, 12... Water tank Shio, 13... Water injection pipe, 14... Water injection valve, 15... Pressure equalization pipe, 15a...
Rising pipe, 15b... rising pipe. Applicant's agent Hisashi Hatano Figure 1 Figure 2 Figure 3 Stone sequence 1 Wood surface (1) Figure 4 Figure 5

Claims (1)

[Claims] 1. An emergency core cooling system water storage tank is installed at a higher location than the reactor pressure vessel, and the water storage tank and the reactor pressure vessel are connected by a water injection pipe equipped with a water injection valve, In the emergency core cooling system, the water injection valve is opened in the event of a loss of coolant accident in a nuclear reactor, and the coolant in the water storage tank is replenished into the reactor pressure vessel by the action of gravity. 1. An emergency core cooling system, characterized in that the water storage tank is configured as a container, communicates with the reactor pressure vessel via a pressure equalization pipe, and is configured to constantly maintain the water storage tank at substantially the same pressure as the inside of the reactor pressure vessel. 2. The emergency core cooling system according to claim 1, wherein the pressure equalization pipe has a riser pipe extending upward from the top of the water storage tank and a fall pipe continuing from the upper end of the riser pipe. 3. The emergency system according to claim 1, wherein the pressure equalizing pipe extends from the top of the water storage tank, and its tip is connected to the upper side wall of the reactor pressure vessel at a high position above the water surface level in the pressure vessel. Reactor core cooling system.