JPH04258794A - Pressure accumulator injection tank for nuclear reactor emergency cooling water feeder - Google Patents

Abstract

PURPOSE:To switch the injection flow from single pressure accumulator injection tank to a primary cooling system without using low/high-pressure injection pumps. CONSTITUTION:A pressure accumulator injection tank 12 has a cooling water injection pipe 14 opened at the inside and a floating valve assembly 31 floated on the surface of the emergency cooling water when the emergency cooling water exists at the preset level or above. The cooling water injection pipe 14 can be connected to a primary cooling system, a large-flow port 20 and a small-flow port 21 are formed at the opening section, both the large-flow port 20 and small-flow port 21 are opened when the emergency cooling water is at the preset level or above, and the large-flow port 20 is closed when the emergency cooling water is decreased to the preset level or below.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an emergency cooling water supply system for a nuclear reactor, and more particularly to an accumulator injection tank used in the system.

0002

2. Description of the Related Art FIG. 3 schematically shows a primary cooling system of a typical conventional two-loop pressurized water reactor having two steam generators 2 and two primary coolant pumps 3.
The primary cooling system equipment includes a reactor vessel 1, a steam generator 2, a primary coolant circulation pump 3, and a primary cooling system loop 6 consisting of primary coolant pipes 5 and 7 that connect these to form a closed circuit.
, and a pressurizer 4.

The primary coolant heated in the reactor core 10 in the reactor vessel 1 is transferred from the reactor vessel 1 to the U-shaped heat exchanger tubes 8 in the vertically installed steam generator 2 via the high-temperature side piping 5 of each loop 6. There, heat is exchanged with the secondary coolant flowing around the heat transfer tubes 8. The primary coolant thus cooled by the steam generator 2 is given a water head by the primary coolant circulation pump 3, and is returned to the reactor vessel 1 via the low temperature side pipe 7.

However, accidents that cause a large drop in the primary cooling system pressure and activate the emergency cooling water supply system,
For example, in the event of a loss of primary coolant accident due to a rupture of a piping or other part of the primary cooling system as shown by reference numeral 9, the primary coolant leaks out of the system from the piping rupture part 9, causing the core to
0 is exposed once. In this case, the reactor is designed to be shut down immediately after the accident occurs, but since nuclear fuel is present in the reactor core, core decay heat is still generated even after the reactor is shut down. If the reactor core remains exposed for a long period of time and the reactor core is not cooled sufficiently, this decay heat could lead to the worst case scenario, such as core meltdown, although this may not actually occur, but it is considered a hypothetical accident. It will be done. Therefore, in the event of a loss of primary coolant accident, it is important to inject emergency core cooling water into the primary cooling system and to supply and accumulate the injected cooling water into the core efficiently and quickly. A cooling water supply device is provided.

[0005] The conventional emergency cooling water supply system includes a pressure accumulation injection system device consisting of a pressure accumulation injection tank 12 and a high pressure injection pump 1.
It consists of high pressure injection system equipment including 9 etc. and low pressure injection system equipment including low pressure injection pump 18 etc. Although only one accumulator injection tank 12 is shown in FIG. 3, one accumulator injection tank is normally used for each loop of the primary cooling system, and the accumulator injection tank 12 is also used in emergency situations. As cooling water, boric acid water 13 is constantly pressurized with nitrogen gas 11, and in the event of a loss of coolant accident, the check valve 15 will automatically open as the pressure in the primary cooling system is reduced, and the cooling water will be Boric acid water 13 is injected into the low-pressure side pipe 7 of the primary cooling system via the injection pipe 14. Furthermore, the low-pressure injection pump 18 and the high-pressure injection pump 19 use a fuel exchange water tank (not shown) storing boric acid water as a water source to fill the reactor cavity with water during fuel exchange. After the water is discharged from the tank 12, the high-pressure injection pump 19 and the low-pressure injection pump 18 are operated in this order to inject water into the primary cooling system over a long period of time.

The reason why the emergency cooling water supply system is configured to include the pressure accumulation injection tank 12, the low pressure injection pump 18, and the high pressure injection pump 19 as described above is that by combining these facilities, various types of primary cooling can be achieved. This is to realize appropriate and safe injection of cooling water even when system pressure changes.

To explain the water injection stage in detail, when a primary coolant loss accident occurs, water is injected into the temporarily empty reactor vessel 1 and the lower plenum part 1 of the reactor vessel 1 is filled with water.
7 is first filled with water (refill stage), then the downcomer section 16 is filled with water, and the reactor core 10 is gradually submerged with water by the water head of the downcomer section 16 (core re-submersion stage). When the reactor core 10 is submerged, the steam generated in the high-temperature reactor core 10 is released to the outside of the primary cooling system, causing a pressure loss, so that the reactor core 10 is submerged slowly. In this way, at the beginning of the refill stage and core re-flooding stage, it is necessary to inject a large amount of water to quickly fill the lower plenum section 17 and downcomer section 16 with water, but after the core re-flooding stage, it is necessary to inject a large amount of water. A small amount of water is sufficient.

FIG. 4 shows a typical example of the injection flow rate required for the above-mentioned emergency cooling water supply system, with time plotted on the horizontal axis. When the pressure decreases and becomes equal to or lower than the holding pressure of the boric acid water 13 in the pressure accumulation injection tank 12, water injection from the pressure accumulation injection tank 12 to the primary cooling system begins (in Fig. 4, approximately 10 seconds after the accident occurred). rear). Due to the reduced pressure in the primary cooling system, the amount of water injected from the pressure accumulation injection tank 12 increases as shown by a curve 28. Then, as the volume of the boric acid water 13 in the pressure accumulation injection tank 12 decreases due to injection into the primary cooling system, and the pressure inside the tank decreases (after about 20 seconds), the amount of water injected into the primary cooling system decreases as shown in curve 29. It gradually decreases as shown in . After the initial stage of core re-flooding (approximately 80 seconds later), the low and high pressure injection pumps 18 and 19 inject water as shown by a curve 30.

[0009]

[Problems to be Solved by the Invention] As described above, in the conventional emergency cooling water supply system, in order to perform the desired water injection,
In addition to the pressure accumulation injection tank, low-pressure injection pumps, high-pressure injection pumps, and associated equipment are also required.
The complexity of the emergency cooling water injection device cannot be avoided, resulting in problems such as not only an increase in manufacturing costs but also a decrease in operational reliability.

[0010] Accordingly, an object of the present invention is to provide a simple reactor emergency cooling water supply system that can switch or change the water injection flow rate from one pressure accumulation injection tank without using a low/high pressure injection pump. .

[0011]

[Means for Solving the Problems] In order to achieve this object, a pressure accumulation injection tank of a nuclear reactor emergency cooling water supply system that stores emergency cooling water under pressure to be supplied to a primary cooling system is provided according to the present invention. , a cooling water injection pipe that penetrates the bottom of the pressure accumulation injection tank, extends into the inside of the pressure accumulation injection tank, and has an end portion that opens inside the pressure accumulation injection tank; A floating valve assembly that floats on the surface of the emergency cooling water when the emergency cooling water is present at a predetermined water level or higher.

The cooling water injection pipe is capable of communicating with the primary cooling system, and has a large flow port and a small flow port formed at its end portion, and the floating valve assembly allows the emergency cooling water to be supplied to a predetermined level. When the water level is above the water level, both the large flow port and the small flow port are opened, and when the emergency cooling water drops below a predetermined water level, the large flow port is closed.

[0013]

[Operation] Normally, the emergency cooling water is maintained at a predetermined water level or higher in the pressure accumulation injection tank, and the floating valve assembly is floating on the liquid level of the emergency cooling water. The flow port is open. If a loss of coolant accident occurs in the primary cooling system in this state, the pressure balance between the primary cooling system and the pressure accumulation injection tank will collapse, and the emergency cooling water in the pressure accumulation injection tank will flow to both the large flow port and the small flow port. The water flows into the cooling water injection pipe at a large flow rate, and is injected into the primary cooling system via the check valve installed there.

[0014] Due to this injection, the liquid level of the emergency cooling water in the pressure accumulation injection tank falls below a predetermined water level, and the floating valve assembly also lowers accordingly, and the large flow port is closed by the floating valve assembly. Subsequent injection of cooling water into the primary cooling system is performed at a small flow rate that flows into the cooling water injection pipe from the small flow port.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which the same reference numerals indicate the same or corresponding parts.

Referring to the drawings, FIGS. 1 and 2 illustrate an accumulator injection tank 12 and a floating valve assembly 31 disposed therein in accordance with the present invention. A pipe 26 having a pressure reducing valve 25 for degassing the tank and lowering the pressure is connected near the top of the pressure accumulation injection tank 12, and a pipe 26 extending into the tank is connected to the bottom of the tank. A cooling water injection pipe 14 that opens there is connected. Further, in the pressure accumulation injection tank 12, a floating valve assembly 31 which normally floats on the boric acid water 13, which is emergency cooling water, is provided.

The end of the pipe 14 that opens into the tank 12 is shaped like a funnel with a conical opening at the top, and defines a large flow port 20. A cylindrical body 27 attached by appropriate means in fluid communication with the interior of the pipe 14 defines a small flow port 21 .

On the other hand, the floating valve assembly 31 is connected to the small fluid port 2.
A spherical valve body 2 having an outer shape or diameter capable of closing 1
2, and a spherical float 24 connected to the valve body 22 by a suitable bending or deformable connecting means such as a chain 23. The float 24 has sufficient buoyancy to float the valve body 22 in the boric acid water 13, as shown in FIG. 1, which would otherwise sink due to its own weight.

Under normal conditions or in the event of a non-coolant loss accident, the boric acid solution 13 is maintained at the upper limit water level in the pressure accumulation injection tank 12, so the float 24 of the floating valve assembly 31 is configured to absorb the boric acid solution 13 as shown in FIG. The valve body 22 , which is floating on the liquid level and connected thereto via a chain 23 , also floats above the end portion of the pipe 14 , and the large flow port 20 is not blocked by the valve body 22 .

Now, assuming that a primary coolant loss accident occurs under the above-mentioned conditions, the pressure in the primary cooling system will drop below the holding pressure in the pressure accumulation injection tank 12, so the pressure accumulation injection tank 12 will of pressurized gas, i.e. nitrogen gas 1
With the help of pressure 1, the injection of boric acid water 13 into the primary cooling system via piping 14 having check valve 15 (see FIG. 3) is started. At this point, as described above, both the large flow port 20 and the small flow port 21 are open, so in the refill stage and the early stage of the core re-flooding stage, the boric acid water 13 is injected into the primary cooling system through the pipe 14 at a large flow rate from both the large flow port 20 and the small flow port 21.

As this injection continues, the pressure accumulation injection tank 1
When the liquid level in 2 drops to a predetermined water level, the floating valve assembly 31
also decreases. When the liquid level in the pressure accumulation injection tank 12 falls to the above-mentioned predetermined water level, which corresponds to the time when the reactor core re-flooding stage begins at the beginning and thereafter, that is, when the amount of water injected into the primary cooling system switches from a large flow rate to a small flow rate, The valve body 22 is attracted by the flow directed toward the large flow port 20 and is moved toward the large flow port 20.
In order to close the cooling system, the amount of water injected into the primary cooling system is switched to a small flow rate from only the small flow port 21 indicated by the symbol b in FIG.

Volume of pressure accumulation injection tank 12, small flow port 21
The cross-sectional area etc. of the pressure accumulation injection tank 12 at the small flow rate mentioned above are
Since the liquid level in the pressure accumulation injection tank 12 is maintained above the large flow port 20 while the water injection function is expected to occur, non-condensable nitrogen gas 11 will not enter the primary cooling system. There's nothing to do.

[0023] Incidentally, the pressure reducing valve 25 in the pipe 26 provided near the top of the pressure accumulation injection tank 12 is opened at an appropriate time.
By removing the nitrogen gas 11 in the pressure accumulation injection tank 12 and reducing the internal pressure of the tank, the amount of water injected into the primary cooling system per unit time is reduced, and the injection period from the pressure accumulation injection tank 12 to the primary cooling system is reduced. It is possible to extend further.

[0024]

As described above, according to the present invention, a large flow port and a small flow port are defined at the end portions of the primary cooling system injection pipe that fluidly communicates with the inside of the pressure accumulation injection tank, and A floating valve assembly with a size that can close the large flow port when the liquid level drops is installed inside the tank, making it possible to use a low-pressure injection pump or high-pressure injection pump that was required for conventional emergency cooling water supply systems. It is possible to switch the amount of cooling water to the primary cooling system, simplifying the system, reducing manufacturing costs, and improving operational reliability.

Furthermore, in a preferred embodiment, since a pressure reducing valve is provided in the pipe connected to the top of the pressure accumulation injection tank, this pressure reduction valve is opened at an appropriate time to remove the inside of the pressure accumulation injection tank. By discharging and reducing the pressure of the pressurized gas, it is possible to extend the cooling water injection period from the pressure accumulation injection tank to the primary cooling system.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a pressure accumulation injection tank of the present invention used in a nuclear reactor emergency cooling water supply system.

FIG. 2 is an enlarged elevational view, partially omitted, showing a floating valve assembly provided in the pressure accumulation injection tank of FIG. 1;

FIG. 3 is a schematic diagram showing a nuclear reactor primary cooling system including a conventional emergency cooling water supply system.

FIG. 4 is a curve diagram showing a typical example of a cooling water injection curve using the emergency cooling water supply device of FIG. 3;

[Explanation of symbols]

12 Pressure accumulation injection tank 13 Emergency cooling water (boric acid water) 14
Cooling water injection pipe 20 Large flow port 21 of cooling water injection pipe
Cooling water injection pipe small flow port 31 Floating valve assembly

Claims (1)

[Claims] Claim 1: A pressure accumulation injection tank for a reactor emergency cooling water supply system that stores emergency cooling water under pressure to be supplied to the primary cooling system, the pressure accumulation injection tank extending through the bottom of the tank and extending into the inside of the pressure accumulation injection tank. It has an end portion that is inserted and opens inside the same, and
A cooling water injection pipe that can communicate with the primary cooling system and has a large flow port and a small flow port formed in the end portion; When the emergency cooling water exists above a predetermined water level, floating on the liquid surface of the emergency cooling water and opening the large flow port and the small flow port, and when the emergency cooling water drops below the predetermined water level, and a floating valve assembly configured to close the large flow port.