JPH0715506B2 - Emergency core cooling system for pressurized water reactors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Object of the invention [Industrial field of application] The present invention provides an emergency core cooling system suitable for a reactor accident in which an emergency core cooling system operates in a reactor power plant. It concerns the improvement of equipment.

[Prior Art] FIG. 3 is a system diagram showing a primary cooling system of a two-loop plant having two steam generators and two primary coolant pumps. However, a part of the loop is omitted in this figure.

The primary cooling system equipment of a pressurized water reactor includes a reactor vessel 1, a steam generator 2, a primary coolant pump 3, and a primary cooling system closed loop 6 including a primary coolant pipe connecting these components and a heating unit. It is composed of a pressure device 4.

The primary coolant heated in the reactor core 10 in the reactor vessel is transported from the reactor vessel 1 to the steam generator 2 through the high temperature side pipe 5, and there through the heat transfer pipe 8 in the steam generator 2. Heat is exchanged with the next coolant. Then, the primary coolant cooled by the steam generator is provided with a head of water by the primary coolant pump 3, and is supplied again to the reactor vessel 1 through the low temperature side pipe 7. Although not shown, in the steam generator 2, the water in the secondary cooling system that does not contain radioactive substances is converted into steam and supplied to the turbine system.

By the way, an accident in which the emergency core cooling device is activated by causing a large pressure drop of the primary cooling system pressure, for example, 1
In the event of a breakage in the piping of the secondary cooling system, that is, in the event of the loss of the primary coolant, the core 10 is once exposed by the outflow of the primary coolant from the broken pipe 9 and then the emergency core cooling system. The operation will cause the reactor core to be flooded and the accident will end.
However, it is necessary to continuously remove core decay heat even after the reactor is shut down, and the emergency core cooling equipment is also required to have a long-term core cooling function.

Therefore, in the conventional emergency core cooling equipment of the pressurized water nuclear power plant, immediately after the accident, a large amount of emergency cooling water is injected into the low temperature side pipe 7 of the primary cooling water loop to accumulate the pressure in the reactor vessel. System water injection equipment (pressure accumulator 12), coolant consumed during core re-submersion, and pump injection equipment 13 and 14 for replenishing the vapor emission of coolant due to core decay heat for a long period thereafter There is.

Here, as shown in FIG. 3, the pressure accumulator 12 of the accumulator system water injection equipment has the accumulator injection water 12a as an emergency cooling water inside, and the pressurized nitrogen gas 12b is enclosed in the liquid level upper part. ing. Further, the liquid phase portion communicates with the low temperature side pipe 7 via the check valve 11 through the pipe 18 and is 1 when the primary coolant loss accident occurs.
The pressure of the next system is the holding pressure of the accumulator (pressure of the pressurized charged gas)
When the pressure falls below the level, the check valve 11 automatically operates to inject the accumulator injection water 12a into the primary cooling system to urgently cool the core 10.

On the other hand, the pump injection facility activates the low-pressure injection pump 13a with a low dead pressure and the high-pressure injection pump 14a with a high dead pressure, which uses the emergency cooling water tank 15 as a water source, so that the low-temperature side pipe 7 changes the primary cooling system Inject emergency cooling water. Here, the function of the low-pressure injection pump 13a is to maintain the core flooding after injection of the pressure accumulator 12 by injecting a large amount of emergency cooling water at the time of large break LOCA when the pressure of the primary cooling system 6 is sufficiently reduced. , The high-pressure injection pump 14a is a high-pressure injection pump 14a at the time of a small break LOCA in which the pressure of the primary cooling system does not drop to the set pressure of the accumulator 12 and the dead pressure of the low-pressure injection pump 13a.
a Alone to maintain the flooding of the core by replenishing the amount of transpiration due to core decay heat, and cooling the core for a long time.

[Problems to be Solved by the Invention] Although the emergency core cooling equipment (referred to as technology A) including these accumulator, low-pressure injection pump, and high-pressure injection pump is functionally excellent, For small break LOCA,
Since the pressure accumulator does not operate, it is necessary to increase the capacity of the high pressure injection pump accordingly.

On the other hand, there is also a method similar to a pressure accumulator using nitrogen gas as a driving source, in which the own weight of water held in the tank is injected as the driving force instead of the nitrogen gas pressure (see, for example, Japanese Patent Publication No. 61-23518). In this technology, the upper part of the cooling water tank and the gas phase part of the reactor pressure vessel are connected by piping, while the lower part of the cooling water tank and the liquid phase part of the reactor pressure vessel are normally closed. In the event of a loss of coolant, the isolation valve for the low pressure signal of the reactor pressure vessel 1 is opened to open the cooling water tank and open the cooling water tank from the dead weight of the water held by the cooling water tank. The cooling water can be injected into the reactor pressure vessel.

However, in this method, since the drive source of the injection system is only the own weight of the cooling water tank holding water, a large drive force cannot be obtained, and a large amount of injection is performed in a short period of time like the above-mentioned pressure accumulator. Is impossible in reality. Also,
In the case of a pressurized water LWR plant, the entire reactor pressure vessel is in a subcooled state, and even in the event of an accident, depending on the scale of damage, the two-phase state of gas-liquid mixing continues for a long time in the reactor pressure vessel. Even if the upper part of the reactor pressure vessel and the upper part of the cooling water tank are connected by piping, the cooling water flows into the piping, and the cooling water flows into the reactor pressure vessel from the injection pipe due to the dead weight of the cooling water tank. May be impaired and the injection function of the cooling water tank may be significantly impaired.

Therefore, when applying the cooling water tank to a pressurized water type LWR plant, the pressure release pipe connected to the upper part of the cooling water tank must be connected not to the reactor pressure vessel but to the upper part of the pressurizer with a free liquid level. There is.

According to such a conventional technique, in the case of the emergency core cooling equipment having a pressure accumulator (conventional technique A), the pressure accumulator 12, the low pressure injection pump 13a and the high pressure injection pump 1 are provided at the time of a large break LOCA.
Although all of 4a operate to perform core cooling, only the low-pressure injection pump 13a having a large capacity is sufficient for core cooling after the injection of the pressure accumulator, and the injection by the high-pressure injection pump 14a is rather excessive injection. On the other hand, during small break LOCA, pressure accumulator 12
And the high-pressure injection pump 13a alone does not inject the low-pressure injection pump 13a, and the amount of vapor emitted by the core decay heat (second
It is necessary to inject an amount of cooling water which exceeds that of Figure A) (Figure 2B), which makes the conditions for the high pressure injection pump 14a severe. As described above, in the conventional technology, each equipment is provided depending on the magnitude of the breakage accident, and the equipment configuration is not efficient.

On the other hand, the conventional technique (technique B) of injecting by the own weight of the cooling water tank holding water instead of the pressure accumulator cannot obtain a large flow rate in a short time like a pressure accumulator pressurized to a high pressure state with nitrogen gas. It is not suitable for continuous injection with a small flow rate for a long period of time, and when trying to obtain a large flow rate with this technology, the tank position is at a high level and a large-diameter pipe is required, which is economical. It is extremely difficult to use due to the problems of the durability and earthquake resistance. Furthermore, if this technique is applied as it is to a pressurized water type LWR plant in which a vapor phase is hard to form in the upper part of the reactor pressure vessel, as mentioned above, the injection function of the cooling water tank is significantly impaired.

The present invention has been made in view of the above circumstances, and in order to solve the problem that the efficiency of the equipment of the conventional technique is low, the pressure accumulator according to the type of primary coolant accident (the size of breakage) is provided. And the difference in functional requirements for high-pressure injection pumps, and
High-pressure injection pump Focusing on the fact that the required injection amount decreases with the decay of core decay heat in a time-dependent manner (Fig. 2A), use the pressure accumulator 12 as a part of the high-pressure injection system 14 during small break LOCA. This makes it possible to reduce the load (capacity) of the high-pressure injection pump 14a and reduce the capacity of the high-pressure injection pump (FIG. 2D) at the initial stage of the accident when a relatively large amount of coolant needs to be injected. It is an object of the present invention to provide an emergency core cooling system for a pressurized water reactor, which can effectively utilize the system and improve the safety of the reactor.

(B) Structure of the Invention [Means for Solving the Problem] To this end, the emergency core cooling equipment for a pressurized water reactor according to the present invention has a liquid phase part of a pressure accumulator and a primary reactor cooling system. And a gas phase portion of the accumulator and a gas phase portion of the pressurizer through a liquid phase check valve that allows a flow toward the reactor primary cooling system. A pressure accumulator injection system connected by piping through a gas phase check valve that allows a flow toward the gas phase part of the pressure accumulator, and an emergency cooling water tank and the liquid phase reversal of the pressure accumulator injection system. A high-pressure injection system that is connected to the upstream pipe of the stop valve by piping via a pump and a stop valve,
And a low-pressure injection system in which the emergency cooling water tank and the upstream pipe of the liquid phase check valve of the pressure accumulator injection system are connected by a pipe via a pump and a stop valve. It has a feature.

Hereinafter, details of the present invention will be described with reference to the drawings illustrating an embodiment.

In FIG. 1, 101 is a primary cooling system equipment of a pressurized water reactor, and a primary cooling system equipment 101 is a reactor vessel 1, a steam generator 2, a primary coolant pump 3, and a primary connecting them. It is composed of a primary cooling system closed loop 6 composed of a coolant pipe, a pressurizer 4, and an emergency core cooling facility 102.

The emergency core cooling facility 102 includes a pressure accumulator injection system 103 and a low pressure injection system.
It consists of 13 and high pressure injection system 14.

The pressure accumulator injection system 103 includes a pressure accumulator 12 and a liquid phase portion 1 of the accumulator 12
2a is connected to the low temperature side pipe 7 of the primary cooling system closed loop 6 by a pipe 18. A check valve 11 is provided in the pipe 18. The check valve 11 allows only the flow in the direction from the pressure accumulator 12 to the low temperature side pipe 7.

The gas phase portion 12b of the pressure accumulator 12 communicates with the gas phase portion 4a of the pressurizer 4 through the pipe 19. The pipe 19 is provided with a stop valve 17 and a check valve 16. The check valve 16 allows only the flow in the direction from the gas phase portion 4a of the pressurizer to the gas phase portion 12b of the pressure accumulator 12. The low-pressure injection system 13 includes an emergency cooling water tank 15 shared with a high-pressure injection system 14 described later, and the emergency cooling water tank 15 is connected to a pipe 18 upstream of the check valve 11 of the pressure accumulator injection system 103 by a pipe 13b. Connected. Pump 13a, stop valve 13c, 1 is installed in pipe 13b.
3d and check valves 13e and 13f are provided. The check valves 13e and 13f allow only the flow from the emergency cooling water tank 15 to the pipe 18.

The high-pressure injection system 14 includes an emergency cooling water tank 15 that is shared with the low-pressure injection system 13 described above, and the emergency cooling water tank 15 is a pipe 14b.
Is connected to the pipe 18 on the upstream side of the check valve 11 of the pressure accumulator injection system 103. A pump 14a and a stop valve 14 are installed in the pipe 14b.
c, 14d and check valves 14e, 14f are provided. Check valves 14e, 14
f allows only the flow from the emergency cooling water tank 15 to the pipe 18.

[Operation] The operation of the emergency core cooling equipment 102 thus configured is as follows.

The primary coolant heated in the reactor core 10 in the reactor vessel is transported from the reactor vessel 1 to the steam generator 2 through the high temperature side pipe 5, and there through the heat transfer pipe 8 in the steam generator 2. Heat is exchanged with the next coolant. Then, the primary coolant cooled by the steam generator is provided with a head of water by the primary coolant pump 3, and is supplied again to the reactor vessel 1 through the low temperature side pipe 7. Although not shown, in the steam generator 2, the water in the secondary cooling system that does not contain radioactive substances is converted into steam and supplied to the turbine system.

At the time of the primary coolant loss accident, the free liquid level 4c of the pressurizer rapidly decreases due to the coolant flowing out from the break point 9, and reaches the lower end of the pressurizer in a short time. First, in the case of small break LOCA, the primary coolant pump is stopped in the event of an accident.
Since there is almost no pressure difference between the high temperature side pipe 5 to which the pressurizer 4 is connected and the low temperature side pipe 7 to which the pressure accumulator 12 is connected, the pressure difference is higher than the elevation of the free liquid surface 12c of the pressure accumulator. When the pressure level of the pressure gauge is sufficiently low,
Pipe 1 for connecting the accumulator gas phase part 12b and the pressurizer gas phase part 4a even during a small break LOCA in which the pressure of the secondary cooling system 6 does not drop sufficiently.
By opening the stop valve 17 of 9, the pressure accumulator 12 performs injection at a small flow rate and for a long period of time due to its own weight (head difference) (hatched portion in FIG. 2C). In this case, since the driving force is only its own weight, the injection flow rate is small and injection is performed over a long period of time. Since the injection characteristics are almost as shown by the shaded area in FIG. The second together with the injection flow rate of the injection system 14 (Fig. 2D)
The required amount of injected water (vapor emission amount due to core decay heat) shown in FIG. A is preferably satisfied. Next, the case of large break LOCA will be described. At the time of large break LOCA in which the pressure of the primary cooling system 6 rapidly decreases to near atmospheric pressure, the nitrogen enclosed in the pressure accumulator causes the checker 16 to press the pressurizer 4. Via primary cooling system 6
Therefore, even if the pressure of the pressurizer 4 becomes lower than the pressure of the pressure accumulator 12, the nitrogen gas of the pressure accumulator 12 does not flow out to the pressurizer 4, and the nitrogen gas of the gas phase portion 12b of the pressure accumulator 12 is not discharged. 12b
Due to the large pressure difference between the primary cooling system 6 and the primary cooling system 6, a large amount of injection can be performed in a short time with the same injection characteristics as the conventional one.

(C) Effect of the Invention As described above, according to the present invention, the accumulator installed for the conventional large-break LOCA can be effectively used even in the small-break LOCA where the pressure of the primary cooling system does not drop sufficiently. Therefore, the capacity of the high-pressure injection system installed for small break LOCA can be significantly reduced. In addition, the rationalization of the equipment can be achieved thereby, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an emergency core cooling equipment of the present invention, and FIG. 2 is a time dependence of a required amount of high-pressure injection flow rate and a small break LOCA when the emergency core cooling equipment of the present invention is applied. FIG. 3 is a graph showing injection characteristics at the time, and FIG. 3 is a diagram showing a conventional emergency core facility and a primary cooling system. 1 ... Reactor vessel, 2 ... Steam generator, 3 ... Primary coolant pump, 4 ... Pressurizer, 4 ... Gas phase section, 4c ... Free liquid level, 6 ... Primary cooling system Closed loop, 7 ... Low temperature side piping, 11
…… Check valve, 12 …… Accumulator, 13 …… Low pressure injection system, 13a ・ ・ ・
… Low-pressure injection pump, 13b …… Piping, 13c, 13d …… Stop valve, 13
e, 13f …… Check valve, 14 …… High pressure injection system, 14a …… High pressure injection pump, 14b …… Piping, 14c, 14d …… Stop valve, 14e, 14f ……
Check valve, 15 …… Emergency cooling water tank, 16 …… Check valve, 17
...... Stop valve, 18 ...... Piping, 19 ...... Piping, 101 ...... Pressure water reactor primary cooling system equipment, 102 ...... Emergency core cooling equipment, 103 …… Accumulator injection system

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuyoshi Matsuoka 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (56) Reference JP-A-60-259994 (JP, A)

Claims (1)

[Claims] 1. A liquid phase part of a pressure accumulator and a reactor primary cooling system are connected by a pipe through a liquid phase check valve which allows a flow toward the reactor primary cooling system, and A pressure accumulator injection system in which a gas phase portion of the pressure accumulator and a gas phase portion of the pressurizer are connected by piping through a gas phase check valve that allows a flow toward the gas phase portion of the pressure accumulator. And a high-pressure injection system in which an emergency cooling water tank and an upstream pipe of the liquid phase check valve of the accumulator injection system are connected by a pipe via a pump and a stop valve, and the emergency And a low-pressure injection system in which a cooling water tank and an upstream pipe of the liquid phase check valve of the accumulator injection system are connected by a pipe via a pump and a stop valve. Emergency core cooling system for pressurized water reactors