JPH042920B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention provides a method for discharging radioactive iodine that leaks into a secondary containment facility (reactor building) from a light water reactor directly into the outside air under assumed accident conditions. This relates to an emergency gas treatment system installed to prevent radiation from being released into the surrounding area and reduce radiation exposure to the public around the site.

[Background of the invention]

FIG. 4 shows a system diagram of an emergency gas treatment system conventionally installed in a light water reactor, and FIG. 5 shows a cross section of a filter train used in the emergency gas treatment system.

In the emergency gas treatment system, iodine leaked from the reactor containment vessel 1 into the reactor building 2 due to a loss of coolant accident is treated by an iodine removal filter 12 in a filter train 5 and released from the exhaust stack 6 into the atmosphere. It is set up to release into the air.

In the event of a nuclear reactor accident, the emergency gas treatment system described above sends (i) a signal indicating that the detected value of the exhaust radiation monitor in the reactor building 2 has become higher than a predetermined level; (iii) a signal indicating that the detection value of the operating floor radioactivity monitor in the reactor building 2 has become higher than a predetermined level; (iii) a signal indicating that the pressure in the reactor containment vessel 1 has become higher than a predetermined level; or (iv) activated by a signal indicating that the reactor water level has fallen abnormally, or activated by a manual activation signal from the central control room when confirming functionality for testing. The inside of building 2 is maintained at negative pressure to prevent the spread of radioactive materials.

When any of the above activation signals is received in the emergency gas treatment system, the air inside the reactor building 2 is discharged by the exhaust fan 6.
, and the opening of the filter train inlet valve 3 and outlet valve 4, flows into the filter train 5 at a rate of about 100 vol/day while maintaining negative pressure inside the reactor building.

The air flowing into the filter train 5 is
Moisture is removed by a moisture removal device 7 that has the ability to remove 99% or more of water droplets of 5μ, and a heater is installed to prevent the efficiency of the activated carbon filter 12 and the high-performance filter 10 from decreasing due to moisture. 8, the relative humidity is reduced to below 70%. Furthermore, a pre-filter 9 is installed to prevent a decrease in efficiency due to clogging of the high-performance filter 10.
It passes through a high-performance filter 10 that has the ability to remove 99.99% of 0.3μ DOP particles (dioctyl phthalate particles that are a constituent of aerosol used in performance tests of gas purifiers). Most of the solids contained in the air are removed. Thereafter, the air is passed through the fan-equipped space heater 11 installed to heat the activated carbon to approximately 66°C during normal reactor operation in order to prevent deterioration of the iodine charcoal filter.
The radioactive iodine is removed by an iodine charcoal filter 12, passes through a fan-equipped space heater 13, and a high-performance particle filter, and is released into the atmosphere from an exhaust stack 6.

As shown in the above functions, in order to maintain the iodine removal efficiency of the charcoal filter 12, the fan-equipped space heater 1 is operated even during normal reactor operation.
1 and 13, the temperature of the activated carbon used in the charcoal filter 12 is maintained at approximately 66°C.

For this reason, space heaters 11 and 13 with fans
Due to this installation, the filter train 5 has become larger. In addition, space heaters 11 and 13 with fans
Since the equipment must be operated at all times, the operating costs are one of the causes of increased costs.

On the other hand, since the filter train 5 is originally installed inside the reactor building 2, it is hardly affected by the outside air, and the humidity inside the filter train does not increase abnormally during normal operation. .

[Purpose of the invention]

The present invention was made in view of the above circumstances, and
The present invention aims to provide an emergency gas processing device that can reduce the size of the filter train while ensuring a certain level of safety, and reduce the cost of standby operation required to maintain the efficiency of the charcoal filter.

[Summary of the invention]

Next, the principle of the device of the present invention will be briefly described.

In conventional emergency gas treatment systems, in order to maintain the iodine removal efficiency of the iodine charcoal filter, the temperature of the activated carbon in the charcoal filter is controlled by a space heater with a fan to approximately 100% even during normal reactor operation.
The temperature is maintained at 66℃. For this reason, the filter train has become larger, and it has been necessary to keep the fan-equipped space heater in operation at all times.

Therefore, the present invention creates a configuration in which a dehumidifier (dryer) is used to reduce the absolute humidity in the filter train, instead of controlling relative humidity by increasing temperature, which has been used to reduce the humidity in the filter train. , the space heater with fan can be omitted, and the space heater with fan does not need to be constantly operated.

In order to achieve the above objective based on the above-mentioned principle, the emergency gas treatment device according to the present invention is designed to prevent radioactive iodine leaked into the reactor building due to an assumed accident in a light water reactor from being dissipated into the atmosphere. In the emergency gas treatment system (SGTS) installed to prevent The present invention is characterized by providing means for controlling the absolute amount of water vapor in the atmosphere within the filter train according to a value.

[Embodiments of the invention]

Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

This embodiment is an example in which the present invention is applied to the above-mentioned known example to improve it, and FIG. 1 is a diagram corresponding to FIG. 5 in the above-mentioned known example.

The filter train 5' of the embodiment shown in FIG. 1 differs from the known example shown in FIG. 5 in the following points.

A hygrometer 21 and a thermometer 22 are installed on the downstream side (right side in the figure) of the charcoal filter 12.
The detection signal is input to the central control room 18, and the central control room 18 has a function of calculating the absolute humidity in the filter train based on the detection signal.

A filter train inlet valve 3 is installed between the filter train 5' and the reactor building (not shown in this figure).
and the filter train outlet valve 4 between the exhaust pipe 6 and the exhaust pipe 6.
are provided respectively. These valves are located in the central control room 1
It receives a control signal from 8 and operates to open and close.

The downstream (right) side of the inlet valve 3 and the outlet valve 4
A bypass line 20 forming a circulation pipe is provided between the upstream side (left side) of the A check valve 17 is provided which operates upon receiving a command from a control room 18.

The control device in the central control room 18 forcibly closes the three valves 3, 4, and 17 and stops the fan 16 when the humidity in the filter train 5' is less than 70%.

When the humidity reaches 70% or more, valves 3 and 4 are opened, check valve 17 is freed, and fan 16 is turned off.
Activate. As a result, the air in the filter train 5' flows into the bypass line 20, passes through the check valve 17 and the fan 16, is dehumidified by the dehumidifier (dryer) 15, and returns into the filter train 5'. This state continues and the filter train 5'
Hygrometer 2 indicates that the humidity within the room has decreased to less than 70%.
1 and thermometer 22, the fan 16 is stopped, the check valve 17 is closed, and the standby operation ends.

The dehumidifier 15 installed in the bypass line 20 is
Cooling dehumidification equipment using cooling coils or air purifiers, absorption dehumidification equipment using liquid absorbents such as lithium chloride and triethylene glycol, or solid adsorbents such as silica gel, activated alumina, and Adsol. An appropriate one can be arbitrarily selected from adsorption type dehumidification devices and the like.

In the unlikely event that there is an accident in the nuclear reactor and any of the abnormal signals (i) to (iv) described above enter the central control room 18, the central control room 18 will operate the exhaust fan 19 and ,
The inlet valves 3 and 4 are commanded to open to allow the air inside the reactor building to flow through the filter train 5', and the radioactive iodine is removed by the charcoal filter 12 and released into the atmosphere from the exhaust stack 6. During the above operation, the central control room 18 issues a command to stop the fan 16 and a command to forcibly close the check valve 17, causing the air inside the reactor building to bypass the filter train 5' and enter the atmosphere. Preventing the release of

The operating logic of this embodiment is shown in FIG.

Standby operation during normal reactor operation When it is confirmed by the hygrometer 21 and thermometer 22 that the relative humidity in the filter train 5' has reached 70%, automatic signals and central control room 18
In response to either manual signal, the check valve 17 opens, the fan 16 and the dehumidifier (dryer) 15 operate, and standby operation is started. The relative humidity value of 70% is a margin for the relative humidity of 80%, at which the iodine removal efficiency of the charcoal filter begins to decrease, as shown in FIG.

Hygrometer 2 indicates that the relative humidity in filter train 5' has fallen below 70% as standby operation continues.
1. If the temperature is confirmed by the thermometer 22, either an automatic signal or a manual signal from the central control room 18 closes the check valve 17, stops the fan 16 and dehumidifier 15, and ends the standby operation.

Operation in the event of a nuclear reactor accident In the event that an accident occurs in the reactor, (i) a signal indicating that the detected value of the exhaust radioactivity monitor in the reactor building 2 has become higher than a predetermined level; (ii) )
(iii) A signal indicating that the detection value of the operating floor radioactivity monitor in the reactor building 2 has become higher than a predetermined level; (iii) A signal indicating that the pressure in the reactor containment vessel 1 has become higher than a predetermined level; or (iv) a signal indicating that the reactor water level has fallen abnormally, the filter train inlet valve 3 and outlet valve 4 are opened, the exhaust fan 19 is activated, and the air inside the reactor building is By means of a charcoal filter 12 in the air filter train 5',
It is assumed that radioactive iodine can be removed and released into the atmosphere from the exhaust stack 6.

At the same time, the dehumidifier 15 and fan 16 installed in the bypass line 20 stop, and the valve 1
7 is also closed to prevent air within the reactor building from bypassing the filter train 5' and being released into the atmosphere.

FIG. 3 shows how the humidity changes due to the above-mentioned standby operation when the relative humidity of the filter train 5' reaches 80%.

When the relative humidity inside the filter train 5' exceeds 80%, the valve 17 opens with the filter train inlet valve 3 and outlet valve 4 closed, and the fan 16 and dehumidifier 15 operate, and the air inside the filter train 5' is flows into bypass line 20, passes through valve 17 and fan 16, is dehumidified by dehumidifier 15, and returns into filter train 5'. If this state continues and it is confirmed by the hygrometer 21 and thermometer 22 that the relative humidity inside the filter train 5' has decreased to less than 70%, the fan 16 is stopped and the valve 17 is closed to end the standby operation. . In this way, once the relative humidity inside the filter train 5' is lowered, almost no moisture will enter from outside the filter train 5', even if the temperature inside the filter train 5' is not actively raised. As shown in FIG. 3, there is almost no increase in humidity, so there is no need to perform standby operation frequently.

In this example, as is clear from the above-mentioned effects, it is possible to ensure a certain level of safety in preventing iodine from escaping from inside the reactor building, and also to reduce the humidity in the filter train. By changing the control method from relative humidity control based on temperature rise to a control method that reduces the absolute amount of water vapor due to dehumidification, it is possible to improve the iodine removal efficiency of the charcoal filter.

○ Since the heater with fan can be omitted, the filter train can be made smaller. As an example
When installed in a 1100 MWe class light water reactor, the length of the filter train can be reduced to approximately 80% of the conventional length.

○C Since the heater with fan does not have to work all the time, the cost can be reduced.

○The temperature and humidity distribution of the Nichacoal filter becomes uniform, improving the reliability of the filter.

FIG. 6 shows another embodiment of the invention. The difference from the embodiment shown in Fig. 1 is that the dehumidifier (dryer) 1
15 is installed in a position where it can be used both in standby operation and operation in the event of an accident, and the moisture removal device in the filter train is omitted.

As a result, the space equivalent to the size of the moisture removal apparatus of the embodiment shown in FIG. 1 can be reduced, and according to this embodiment, a more economical emergency gas treatment system can be constructed.

〔Effect of the invention〕

As described in detail above, when the present invention is applied, it is possible to ensure the prescribed safety standards for preventing iodine inside the reactor building from being released into the atmosphere, and also to make it possible to downsize the filter train. The cost of standby operation required to maintain the efficiency of the coal filter can be reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram in which a control system is added to a schematic cross-sectional view of a filter train according to an embodiment of the present invention, FIG. 2 is a block diagram showing the logic of the above embodiment, and FIG. It is a chart for explaining the effect of standby operation in an example. Figure 4 is a system diagram of an example of a conventional emergency gas treatment system;
The figure is an explanatory diagram schematically depicting a cross section of a filter line in the above-mentioned conventional example. FIG. 6 is an explanatory diagram showing an embodiment different from the above, and corresponds to FIG. 1 in the embodiment. FIG. 7 is a chart showing the relationship between the iodine removal efficiency of the charcoal filter and the relative humidity. DESCRIPTION OF SYMBOLS 1... Reactor containment vessel, 2... Reactor building, 3... Filter train inlet valve, 4... Filter train outlet valve, 5, 5'... Filter train, 6... Exhaust stack,
7...Demister (moisture removal device), 8...Heating heater (heating coil), 9...Prefilter, 10...High performance particle filter, 11...Space heater with fan, 12...Iodine charcoal filter (activated carbon filter), 13...Space heater with fan, 14
...High performance particle filter, 15...Dehumidifier (dryer),
16... Bypass line installation fan, 17... Check valve, 18... Central control room, 19... Fan (emergency gas processing system exhaust fan), 20... Bypass line, 21
...Hygrometer, 22...Thermometer.

Claims (1)

[Claims] 1. In an emergency gas treatment system (SGTS) installed to prevent radioactive iodine leaked into the reactor building due to an assumed accident in a light water reactor from being dissipated into the atmosphere, a filter train At least one of a hygrometer and a thermometer is installed near the charcoal filter in the filter train, and the absolute amount of water vapor in the atmosphere in the filter train is controlled by the detected values of the hygrometer and thermometer. An emergency gas processing device characterized by being provided with means. 2. The filter train has a circulation pipe connecting its outlet and inlet, and a circulation pump is provided in the circulation pipe to circulate the gas in the filter train. An emergency gas treatment device according to claim 1. 3. The emergency gas treatment device according to claim 2, wherein the circulation pipe is equipped with at least one of a dehumidifier and a dryer. 4. The emergency gas processing device according to claim 2 or 3, wherein the circulation pipe is provided with a valve. 5. The emergency gas processing device according to claim 4, wherein the valve is a check valve.