JPH0636060B2 - Aniulus ventilation system - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an annulus ventilation system for a pressurized water nuclear reactor facility, and particularly to an annulus part in a predetermined negative pressure state at an early stage of a coolant loss accident. It relates to an annulus ventilation system suitable for reconstitution.

[Background of the Invention]

A conventional air-conditioning ventilation system is composed of a ventilation air-conditioning system that operates during normal operation and an air-conditioning purification system that is installed independently of it and that operates during a loss of coolant accident.

FIG. 2 is a system diagram of a conventional Aniulus ventilation system. In the figure, the annulus portion (the space inside the secondary storage container) 5 is
Air is supplied by an air supply fan system including an air supply fan 6, an air supply filter unit 7 for removing dust in the air supply, and an isolation valve 8 for isolating the annulus portion 5 in the event of an accident. Further, during normal operation, the exhaust gas is exhausted from the exhaust stack 4 by the annulus exhaust system including the exhaust fan 9 and the exhaust pipe 10. Aniulus air supply system and Aniulus exhaust system
It constitutes a ventilation and air conditioning system.

On the other hand, the secondary PCV gas treatment system of the pressurized water reactor, that is, the annulus purification system is installed independently of the ventilation air conditioning system, and is connected to the annulus purification system piping 1, the annulus purification system fan 2, and the annulus purification system filter unit 3. Becomes
It is connected to the exhaust stack 4. The annulus purification system filter unit 3 is composed of an iodine removal filter that adsorbs radioactive iodine in the exhaust gas in the event of a loss of coolant, a front filter, and a rear filter.

Two Aniulus purification systems are installed with 100% capacity so as to satisfy the single failure criterion in the event of an accident.
Each is designed to get power from an emergency diesel independently.

In this design, the Aniulus purification system is activated upon detection of the loss of coolant incident. The radioactivity leaked from the primary containment vessel to the annulus part though a little is processed by the anilus filter system unit 3 and is released from the exhaust stack 4 because this anilus purification system keeps the annulus part 5 at a negative pressure. I'm sorry.

However, in the initial stage of the coolant loss accident, the temperature inside the primary containment vessel becomes high (about 120 ° C.). This heat is transmitted through the wall surface of the primary containment vessel and heats the annulus portion 5, so that the pressure in the annulus portion 5 temporarily rises. Furthermore, during normal operation, the ventilation and air-conditioning system of the annulus section operates, and
However, if the external power supply is lost in the event of an accident, the ventilation air-conditioning system for the annulus will stop at the same time as the accident, and the negative pressure will not be maintained. .

As a result, the pressure of the annulus portion 5 rises and becomes a positive pressure when the loss of coolant accident occurs. After that, the anilus part is exhausted by the anilus purification system, but it takes about 8 minutes for the large capacity fan 2 of 14,000 m ³ / h to return to a negative pressure. During this time, the atmosphere in the annulus will leak from the building without being processed by the filter. In this way, if radioactivity is released directly from the building, compared to the case where it is released from an exhaust stack, it is considered that the amount of radiation exposure to surrounding residents at the time of the accident will be higher because the effect of the radioactivity on atmospheric diffusion is lower.

After the accident, after the pressure on the annulus became steady,
It is known that the processing capacity required to hold the negative pressure of the annulus portion 5 is 1/4 or less of that of the conventional example. On the other hand, a large volume of the purification system is required only to alleviate the initial pressure rise in the annulus and make the negative pressure within about 10 minutes. In that sense,
Equipment costs are rising.

[Object of the Invention]

An object of the present invention is to provide an annulus ventilation system that keeps the annulus portion at a negative pressure even in the early stage of a coolant loss accident, without a large increase in equipment.

[Outline of Invention]

In order to achieve the above object, the present invention abolishes the anilus purification system fan, uses the anilus exhaust system fan also as the anilus purification system fan, and exhaust pipes during normal operation and anilus purification at the time of a loss of coolant accident. The system filters are connected so that they can be switched and used.
It is desirable to switch between the two automatically based on the signal that the pressure gauge in the annulus portion detects the pressure increase due to the loss of coolant.

The present invention integrates an annulus ventilation system and an annulus purification system, closes an air supply system by a signal indicating a loss of coolant accident, operates an exhaust fan, bypasses a radioactive material removal filter, and exhausts gas through an exhaust pipe. Therefore, the annulus part can be quickly returned to a sufficient negative pressure, radioactive substances released directly from the annulus part to the environment can be reduced, and after the negative pressure is achieved, an annulus purification system equipped with a filter that removes radioactive substances is used. It is characterized by being able to suppress the release of radioactive substances to the environment because it is exhausted.

Example of Invention

Next, with reference to FIG. 1, one embodiment of the ventilation system of the present invention will be described in detail. In FIG. 1, the second
The parts having the same functions as those of the conventional example in the figure are denoted by the same reference numerals, and the description thereof will be omitted.

Comparing FIG. 1 and FIG. 2, the aniurus purification system fan 2 is eliminated, and the exhaust pipe 10 and the aniurus purification system filter unit 3 are provided on the discharge side of the fan 9 of the aniurus exhaust system.
And are connected in parallel. The isolation valves 11 and 12 are provided as exhaust path switching means for switching and using these parallel parts. The switching is performed by a signal from the annulus portion pressure gauge 14 which is a pressure detecting means. Reference numeral 13 is a return pipe from the exhaust fan 9 to the annulus portion, 16 is an orifice flow control for regulating the flow rate to the filter unit 3, and 15 is an exhaust pipe to the exhaust pipe 4.

Of the ventilation and air-conditioning system that operates during normal operation, the air supply fan 6 of the annulus air supply system is driven by a normal power source as usual. On the other hand, the air supply side isolation valve 8 and the annulus exhaust system are configured to be driven also by the emergency power supply.

In the aniurus ventilation system having such a configuration, during steady operation, the air in the aniurus part is supplied from the air supply fan 6 and the air supply filter 7, and is discharged from the exhaust pipe 4 to the environment via the exhaust fan 9 and the exhaust pipe 10. Exhausted. The capacities of the air supply fan 6 and the exhaust fan 9 are about 3.000 m ³ / h. The temperature of the annulus portion is controlled within the range of 10 to 40 ° C. by this ventilation system. The exhaust fan 9 has a capacity of 15
Those of 000m ³ / h is 3 units disposed, it is adapted to exert a predetermined capacity 30000 m ³ / h in two, 1
The stand is a standby machine.

When a coolant loss accident occurs, the feeder side isolation valve 8 is immediately closed by the operation signal of the emergency core cooling equipment, and the feeder fan 6 is also stopped. As a result, the annulus portion 5 is only exhausted by the exhaust fan 9.

In the event of a loss of coolant, the temperature inside the PCV was approximately 120 ° C.
The pressure rises to a certain degree, the heat is transmitted to the wall surface of the containment vessel, and heats the annulus portion, so the pressure in the annulus portion rises once. However, since the annulus portion 5 is exhausted by the exhaust fan 9 of about 30,000 m ³ / h, the negative pressure is always maintained as shown by the solid line in FIG. During this time, the atmosphere exhausted from the annulus is discharged from the exhaust pipe 4 to the environment via the exhaust pipe 10 without passing through the exhaust filter unit 3. However, as will be described later, since the radiation diffusion effect is good, there is no problem.

Then, after about 5 minutes, when the pressure in the annulus portion 5 becomes sufficiently negative (about -6.4 mmHg), this is detected by the pressure gauge 14 for the annulus portion, the isolation valve 12 is closed, and the exhaust filter isolation valve 1
The operation to open 1 is automatically performed.

After that, the atmosphere of the annulus portion is guided from the exhaust fan 9 to the exhaust filter 3, the radioactive iodine is removed, and the atmosphere is exhausted from the exhaust pipe 4. The exhaust filter starts to operate after the negative pressure is sufficiently achieved.
To maintain the negative pressure, an exhaust capacity of about 4,000 m ³ / h is sufficient, and an exhaust filter capacity of only 4,000 m ³ / h is required. Here, a flow control orifice 16 is provided in front of the exhaust filter 3, only about 4000 m ³ / h is passed through the exhaust filter 3, and the remaining about 26,000 m ³ / h.
Is returned to the annulus portion through the return pipe 13. If only one fan 9 is manually operated at this point, the return flow rate will be 11000 m ³ / h.

According to this embodiment, there are effects of reducing environmental exposure dose at the time of accident and rationalizing equipment costs. Next, it will be described in detail.

In the conventional example, the positive pressure is maintained for about 8 minutes before the negative pressure returns to the negative part. Therefore, the atmosphere in the Aniulus part is
It leaks to the environment through the holes in the annulus and doors.
The radioactivity released into the containment vessel during the loss of coolant accident was
According to the leak rate of the containment vessel, a small amount leaks to the annulus part, so during the initial 8 minutes, radioactivity will be released directly from the building.

On the other hand, in the present invention, since the annulus part is always under negative pressure immediately after the accident, the radioactivity leaked to the annulus part for about 5 minutes until it reaches a sufficient negative pressure does not go through the exhaust filter, but from the exhaust stack. Emitted while being monitored.

Generally, the radioactivity released from the equipment diffuses in the atmosphere and exposes the inhabitants to the surrounding area, but as shown in Fig. 4, the radioactivity diffusion effect greatly differs depending on the height of the radioactivity source. If the same level of radioactivity is released, the exposure dose at the time of stack release (about 50 m) is the building release (ground release).
It is suppressed to about 1/10 of the time.

Therefore, the overall exposure dose is much lower with the present invention.

Next, a comparison between the conventional example and the equipment specifications of the present embodiment is as follows.

As apparent from the above table, this embodiment is typically connected to Aniyurasu ventilation system emergency power supply for at, Although safety grade is seismic A _s class, Aniyurasu purification system Juan 12,000 been made conventionally required m ³ / h × 2 is not required, and the filter capacity is about 12,000 m ³ / h to about 4,000 m ³ / h
Can be reduced to. Compared to the cost increase of the normal Aniulus ventilation system, the effect of reducing the fan and reducing the capacity of the filter of the Aniulus purification system is far greater, so when combined, a large rationalization of equipment costs is achieved. .

It is confirmed that the Aniulus purification system of this example has specifications sufficient as safety equipment. There are three conditions for safety equipment: (1) connection to emergency power supply, (2) safety grade, and (3) single failure criteria.

Regarding (1), since the annulus air supply system isolation valve 8, the anilous exhaust system fan 9, the annulus exhaust system isolation valves 11 and 12, and the annulus portion pressure gauge 14 that should be activated in the event of an accident are connected to the emergency power supply. ,no problem.

For (2) it is addressed by all seismic A _s class Aniyurasu exhaust system.

Regarding (3), the Aniulus exhaust fan 9 is 375 (ie, 15,00 / 4,000)% × 3 of the specification, which satisfies the single failure criterion. Two air supply system isolation valves are installed in series, and two exhaust system valves are installed in parallel. Since the exhaust filter is a static device, 100% × 1 is sufficient.

〔The invention's effect〕

 According to the present invention, the following effects can be obtained.

(1) Since the pressure in the annulus part does not become a positive pressure even in the early stage of the loss of coolant, the atmosphere in the annulus part is constantly monitored and is released only from the stack. Therefore, the atmospheric diffusion effect of radioactivity will increase, and the radiation dose to the local residents at the time of the accident will be reduced.

(2) Since the Anilus purification system fan is deleted and the exhaust filter capacity is smaller than before, the equipment cost is rationalized.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of an anilious ventilation system according to the present invention, FIG. 2 is a system diagram showing an example of a conventional anilious ventilation system, and FIG. 3 is an anilus at the time of an accident of the present invention and a conventional example. FIG. 4 is a diagram showing a change in part pressure, and FIG. 4 is a diagram showing a relationship between the height of a radioactive emission source and the exposure dose of residents in the surrounding area. 1 ... Anyura purification system piping, 2 ... Anyura purification system fan, 3 ... Anyura purification system filter unit, 4
…… Exhaust stack, 5 …… Anyurus part, 6 …… Air supply fan,
7 ... Air supply filter, 8 ... Isolation valve, 9 ... Exhaust fan, 10 ... Exhaust piping, 11, 12 ... Isolation valve, 13 ...
... Return pipe, 14 ... pressure gauge for annulus, 15 ... exhaust pipe, 16 ... flow control orifice.

Claims (1)

[Claims] 1. An annulus air supply system for supplying external air to the annulus portion of the pressurized water reactor only during normal operation and stopping the air supply by a signal indicating a loss of coolant accident, and an annulus in the normal operation state. Exhaust gas that has a capacity that satisfies the partial air ventilation conditions and that has an exhaust fan whose suction side is connected to the annulus part and a filter that is connected to the outlet of the exhaust fan via exhaust path switching means to remove radioactive substances in the exhaust gas And an annulus purifying system that guides the exhaust gas to an exhaust pipe, and is arranged in parallel with the annulus purifying system so as to bypass a filter that removes the radioactive substance and is connected to the outlet of the exhaust fan through the exhaust path switching means. Exhaust pipe that guides the exhaust to the exhaust stack, and pressure detection means that detects the pressure of the annulus portion and outputs a pressure signal are included. The switching means when the pressure of the annulus to be outputted from the pressure detecting means is below a predetermined value, it switches the exhaust path from the exhaust pipe to the annulus purification system, annulus ventilation system characterized by.