JPH06347593A - Treatment for radioactive waste gas - Google Patents

Abstract

PURPOSE:To continuously remove humidity in exhaust gas without using freezer and raise reliability and economy. CONSTITUTION:For a dehumidifier cooler or a desiccator, dehumidifier devices 24a, 24b containing hollow yearn membranes 25a, 25b with large steam transmission coefficient are used and the system inside is pressurized to improve steam transmission performance with compressed air and an ejector 12 before the exhaust gas flows in the dehumidifier devices 24a, 24b. To the secondary side of the hollow yearn membranes 25a, 25b, a part of the exhaust gas dried in the dehumidifier devices 24a, 24b is purged. The secondary side of the humidifier devices 24a, 24b is kept depressurized by the vacuum of the turbine main condenser to improve the steam transmission performance and remove the steam component in the exhaust gas most efficiently and the humidity in the exhaust gas is lowered to below a specified percentage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating radioactive gas waste containing radioactive substances, which has an improved method of removing moisture in a dehumidifying cooler and a dehumidifying tower.

[0002]

2. Description of the Related Art In general, a coolant for a boiling water reactor is irradiated with neutrons while passing through the core and partially decomposed into oxygen and hydrogen, and further, ³ H, ¹⁶ N, ¹⁹ O And so on. In addition, from the pinhole etc. which arose in the fuel rod, Kr and X
A radioactive rare gas such as e leaks, and these rare gases are mixed with the coolant and sent to the turbine system. In addition, there is leakage from the outside air into the turbine main condenser of the turbine system.

Due to these radioactive gas wastes (hereinafter referred to as "exhaust gas"), it is necessary for the turbine system in a boiling water nuclear power plant to be shielded like a nuclear reactor to maintain the soundness inside and around the plant.

By the way, since the exhaust gas is generally non-condensable, it accumulates in the steam system, particularly in the turbine main condenser. Therefore, conventionally, the exhaust gas staying in the turbine main condenser is extracted by an air extractor and guided to an activated carbon type rare gas holdup tower for treatment.

FIG. 2 shows an example of this type of conventional exhaust gas treatment apparatus. Exhaust gas accumulated inside the turbine main condenser is extracted by an air extractor 1, and a preheater 3, a recombiner 4 and The hydrogen gas is introduced into the hydrogen recombining device 2 including the condenser 5 and subjected to recombining and volume reduction processing of hydrogen gas.

The exhaust gas guided to the hydrogen recombiner 2 is first preheated by the preheater 3 to a temperature at which oxygen and hydrogen contained in the exhaust gas are efficiently recombined, and then is guided to the downstream recombiner 4. The hydrogen and oxygen in the exhaust gas become steam due to the recombination reaction. Further, in the condenser 5 downstream thereof, the water vapor in the exhaust gas is condensed by cooling with the external cooling water and most of it becomes water, which is separated from the exhaust gas, and the separated water is returned to the turbine main condenser (not shown). Be done.

On the other hand, the exhaust gas from which water is separated and removed is shown in FIG.
As shown in (4), the dehumidifying cooler 6 performs cooling and primary dehumidification, and thereafter, the moisture is sufficiently removed by the dehumidifying tower 7 (7a, 7b), and then the activated carbon rare gas holdup tower 8 is used. Be led to. Then, the radioactive gas (mainly a rare gas such as Kr or Xe) remaining in the exhaust gas is adsorbed on the activated carbon, and after a long hold-up, the vacuum pump 9 discharges it to the atmosphere from the exhaust stack 10.

Each of these devices is separated in a chamber that is airtight or in a similar state, and each chamber is air-conditioned. In particular, as shown in FIG. 2, the activated carbon type rare gas hold-up tower chamber 11 is air-conditioned from the dedicated air-conditioning equipment 12 via the ducts 13 and 14 separately from other general air-conditioning to maintain the adsorption performance of activated carbon. Therefore, the inside temperature of the activated carbon type rare gas holdup tower inlet pipe 15 can be maintained at a low temperature.

FIG. 3 shows the details around the conventional dehumidification tower 7 (7a, 7b). Each dehumidification tower 7 (7a, 7b) has a single exhaust gas treatment capacity of, for example, 40 Nm ³ / h. And
These are connected in parallel via the inlet valves 16a and 16b and the outlet valves 17a and 17b, and during normal operation, only one of the systems performs processing operation and the other system performs defrosting operation. .

That is, each of the dehumidifying towers 7 (7a, 7b)
As shown in FIG. 3, the refrigerating machines 18a and 18b supply and collect the refrigerant to freeze the water vapor in the exhaust gas while evaporating the refrigerant in the tower. Cooling pipe 19a with fins through which the refrigerant flows,
When it flows between the fins of 19b, it is frozen and removed.

[0011]

In the conventional method for treating radioactive gas waste, a direct freezing method using refrigerators 18a, 18b is adopted as a method for removing moisture from exhaust gas in the dehumidifying towers 7a, 7b. Load control range is 0
It is as large as 1000 kCal / h, and there is a problem that it takes a lot of time for the on-site adjustment test of the refrigerators 18a and 18b.

Further, since maintenance is required at the time of regular inspection, running costs are high, and in the current plant,
Approximately one month is required for maintenance of the refrigerators 18a and 18b after each regular inspection. Further, since the refrigerators 18a and 18b are dynamic devices, there are problems such as deterioration over time.

The present invention has been made to solve the above-mentioned problems, and it is possible to continuously remove moisture in exhaust gas without using a refrigerator, and to obtain high reliability and economic efficiency. It is an object to provide a method for treating gaseous waste.

[0014]

The present invention introduces radioactive gas waste generated in a nuclear power plant from a main condenser through an air extractor to a hydrogen recombiner to recombine and reduce the volume of hydrogen gas. In addition to conducting the exhaust gas from the hydrogen recombiner to the dehumidifying cooler for cooling and primary dehumidification, then introducing this exhaust gas to the dehumidifying tower to remove moisture, and then to the activated carbon rare gas hold-up tower. In a method for treating radioactive gas waste by conducting a delayed treatment by using a dehumidifying device having a hollow fiber membrane having a large water vapor transmission coefficient incorporated in the dehumidifying cooler or the dehumidifying tower, before the exhaust gas flows into the dehumidifying device. To improve the water vapor permeation performance by pressurizing the inside of the system with pressurized air and an ejector, and using a part of the exhaust gas dried by this dehumidifier on the secondary side of the hollow fiber membrane for purging, To further improve the water vapor permeability by maintaining the secondary side by the vacuum pressure of the serial main condenser to the vacuum,
It is characterized in that the humidity of exhaust gas is set to a required percentage, for example, 40% or less.

When the humidity of the required percentage or less cannot be obtained due to the condition of the dehumidifier, the humidity is detected by the dew point meter installed in the system, and the dehumidifier is replaced with a spare hollow fiber membrane. It is characterized by ensuring performance.

Further, when the dehumidifying performance cannot be ensured even in the spare dehumidifying device, the humidity is detected by the dew point meter installed in the system and the system is switched to the circulation line to the main condenser to obtain the moistening. It is characterized by blocking the flow of gas downstream and protecting the system.

[0017]

In the method for treating radioactive gaseous waste according to the present invention, a dehumidifying device containing a hollow fiber membrane having a large water vapor permeability coefficient is used as a dehumidifying cooler, or as a dehumidifying cooler and a dehumidifying tower. Is introduced into the dehumidifier, is pressurized, and passes through the hollow fiber membrane. Water vapor permeation performance is improved by pressurizing the inside of the system with pressurized air and an ejector.

In this state, a part of the exhaust gas dried by the dehumidifier is used for purging, is supplied to the outside of the hollow fiber membrane, and the vacuum pressure of the main condenser is used to form a vacuum. When the pressure is reduced, the water vapor transmission performance is further improved, and the water vapor content in the exhaust gas is most efficiently removed. That is, the water vapor content in the exhaust gas is removed by permeating the hollow fiber membrane, and the humidity of the exhaust gas becomes a required percentage or less, for example 40% or less.

Further, when the humidity of the required percentage or less cannot be obtained due to the condition of the dehumidifier, the humidity is detected by the dew point meter installed in the system, and the dehumidifier equipped with a spare hollow fiber membrane is used. Dehumidification performance can be secured.

When the dehumidification performance cannot be ensured even in the standby dehumidification device provided for standby, the humidity is detected by the dew point meter installed in the system, and the dehumidification meter is installed in the circulation line to the main condenser. Switching the system prevents the wet gas from flowing to the downstream side and protects the system.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the method for treating radioactive gaseous waste according to the present invention will be described with reference to FIG. The present invention is
It has a feature in the pressurization system of the exhaust gas flowing into the dehumidification device containing the hollow fiber membrane, the moisture removal method in the dehumidification device and the emergency switching system, and the treatment method of radioactive gas waste in other parts is Since it is the same as the conventional exhaust gas treatment apparatus shown in FIG. 2, only the part that is the gist of the present invention will be illustrated and described below, and description of the same parts as the conventional example will be omitted.

FIG. 1 shows a dehumidifying device 24 in an exhaust gas treatment device.
(24a, 24b) shows the configuration around, in the figure, reference numeral 21
Is an ejector, which bleeds air from the condenser 5 by opening the pressurized air amount adjusting valve 20 to pressurize the system, and the pressurizing state is to check the pressurizing pressure with the pressurizing pressure gauge 22. is there.

The dehumidifiers 24a and 24b are the dehumidifier inlet valve 23.
a, 23b and dehumidifier outlet valves 26a, 26b are connected in parallel so that only one system is operated during normal operation.

As shown in FIG. 1, hollow fiber membranes 25 (25a, 25b) having a large water vapor transmission coefficient are provided in the dehumidifiers 24a, 24b.
The exhaust gas pressurized by the ejector 21 passes through the inside of each of the hollow fiber membranes 25a and 25b.

The inside of each of these dehumidifying devices 24a and 24b is shown in FIG.
As shown in FIG. 3, a part of the dried exhaust gas treated by the dehumidifiers 24a and 24b is used as purge air, the flow rate is adjusted by the purge air amount adjusting valve 27, and the purge air pressure adjusting valve is set by the set pressure of the purge air pressure gauge 30. While the pressure is adjusted by 31, the vacuum pressure of the main condenser is used to reduce the pressure by vacuuming.

As a result, the water vapor in the exhaust gas flowing through the hollow fiber membranes 25a and 25b is separated and removed by passing through the hollow fiber membranes 25a and 25b, and the relative humidity of the exhaust gas is reduced to the required percentage, for example, about 40%. It has become less than or equal to%. This is because the exhaust gas supplied to the activated carbon type rare gas holdup tower 8 needs to have a relative humidity of 40% or less.

Also, the purge air can be selected by switching the purge air inlet valves 28a and 28b and the purge air outlet valves 29a and 29b to the operating system of the processing apparatus.

Next, a method of removing moisture in each of the dehumidifiers 24a and 24b will be described. In FIG. 1, the dehumidifying device 24a
Assuming that the system on the other side is in the treatment operation, the condenser 5
The steam is cooled by, and the condensed exhaust gas pressurizes the system by bleeding by flowing pressurized air whose flow rate is adjusted by the pressurized air amount adjusting valve 20 to the ejector 21, and the pressurization status is the pressurization pressure gauge. Check the pressurization status with 22. The pressurized exhaust gas is guided to the dehumidifier 24a via the dehumidifier inlet valve 23a and passes through the hollow fiber membrane 25a.

At this time, the inside of the dehumidifying device 24a is
A part of the exhaust gas dried by a is used as purge air and is adjusted to an appropriate flow rate by the purge air amount adjusting valve 27, and the purge air is dehumidified by the dehumidifier 24 via the purge air inlet valve 28a.
Flow inside a to improve water vapor transmission performance.

Further, in order to evacuate the inside of the dehumidifier 24a and maintain the reduced pressure, the degree of vacuum of the main condenser is used, and according to the set value of the purge air pressure gauge 30 via the purge air outlet valve 29a. The pressure is adjusted by the purge air pressure adjusting valve 31.
As a result, an appropriate vacuum is drawn, so the hollow fiber membrane 25
The water vapor content in the exhaust gas flowing through the inside a is removed by passing through the hollow fiber membrane 25a, and is discharged to the main condenser.

Therefore, the exhaust gas after passing through the dehumidifier 24a has a relative humidity of the required percentage, for example, 40%.
The following is introduced to the activated carbon type rare gas holdup tower 8 (see FIG. 2) through the dehumidifier outlet valve 26a, and the delay processing is performed.

Since the dry exhaust gas flowing out from the dehumidifier 24a is used as a part of the purge air for the hollow fiber membrane 25a, an appropriate amount is set by the purge air amount adjusting valve 27 at the dehumidifier outlet flow meter 32 that monitors the flow rate of the system. decide. The system pressure of the dehumidifier 24a is adjusted to a set value by the dehumidifier outlet pressure adjusting valve 34 according to the instruction value of the dehumidifier outlet pressure gauge 35.

When trouble occurs in the dehumidifier 24a and the dew point meter 33 at the outlet of the dehumidifier 24a becomes larger than the set value, the dehumidifier inlet valve 23a, the dehumidifier outlet valve 26a, the purge air inlet valve 28a and The purge air outlet valve 29a is closed. Along with this, the dehumidifier inlet valve 23b, the dehumidifier outlet valve 26b, the purge air inlet valve 28b and the purge air outlet valve.
29b is opened and the system is switched to the dehumidifier 24b side.

Even if the dehumidifiers 24a and 24b are switched to each other and the dew point meter 33 still exceeds the set value, the activated carbon type rare gas holdup tower inlet valve is used.
36 is closed, the circulation line main valve 37 is opened, the circulation line to the main condenser is activated, and the safety of the system is ensured. At this time, the system pressure is adjusted by the circulation line pressure adjusting valve 38.

[0035]

According to the present invention, the dehumidifying cooler and the refrigerator, which are used for the primary cooling, are unnecessary, and the internal adjustment can be omitted. In addition, maintenance at the time of regular inspection becomes easy, and the period can be shortened to about 1/4.
Further, since the refrigerator is not required, the space required for the dehumidifying device can be reduced by half, and the size of the dehumidifying device itself can be reduced to about 1/5 by volume.

[Brief description of drawings]

FIG. 1 is a system diagram showing around a system pressurizing ejector and around a dehumidifying device in an embodiment of a method for treating radioactive gas waste according to the present invention.

FIG. 2 is a system diagram showing a conventional radioactive waste treatment device.

FIG. 3 is a system diagram showing the dehumidifying tower and its surroundings in FIG.

[Explanation of symbols]

1 ... Air extractor, 2 ... Hydrogen recombiner, 3 ... Preheater, 4
... Recombiner, 5 ... Condenser, 6 ... Dehumidifying cooler, 7 ... Dehumidifying tower, 8 ... Activated carbon type rare gas hold-up tower, 9 ... Vacuum pump, 10 ... Exhaust pipe, 11 ... Activated carbon type rare gas hold Up tower room, 12 ... Air conditioning equipment, 13, 14 ... Duct, 15 ... Activated carbon type rare gas holdup tower inlet piping, 16 ... Dehumidification tower inlet valve, 17
... Dehumidifying tower outlet valve, 18 ... Refrigerator, 19 ... Cooling pipe, 20 ... Pressurized air amount adjusting valve, 21 ... Ejector, 22 ... Pressurizing pressure gauge, 23 ... Dehumidifier inlet valve, 24 ... Dehumidifier, 25 ... Hollow fiber membrane, 26 ... Dehumidifier outlet valve, 27 ... Purge air amount adjusting valve, 28 ... Purge air inlet valve, 29 ... Purge air outlet valve, 30 ... Purge air pressure gauge,
31 ... Purge air pressure adjusting valve, 32 ... Dehumidifier outlet flow meter,
33 ... Dew point meter, 34 ... Dehumidifier outlet pressure adjustment valve, 35 ... Dehumidifier outlet pressure gauge, 36 ... Activated carbon rare gas holdup tower inlet valve, 37 ... Circulation line main valve, 38 ... Circulation line pressure adjustment valve.

Claims (4)

[Claims] 1. A radioactive gas waste generated in a nuclear power plant is introduced from a main condenser through an air extractor to a hydrogen recombiner for recombining and reducing the volume of hydrogen gas, and at the same time, recombining hydrogen. The exhaust gas from the reactor is guided to the dehumidifying cooler for cooling and primary dehumidification, and then this exhaust gas is guided to the dehumidifying tower to remove moisture, and then to the activated carbon rare gas holdup tower for delay treatment. In the method for treating gaseous waste, a dehumidifying device having a hollow fiber membrane having a large water vapor permeability coefficient in the dehumidifying cooler or the dehumidifying tower is used to pressurize the system before exhaust gas flows into the dehumidifying device, Part of the exhaust gas dried by this dehumidifying device is used for purging on the secondary side of the hollow fiber membrane, and the secondary side is kept at a reduced pressure by the vacuum pressure of the main condenser. How to process . 2. When the humidity of the required percentage or less cannot be obtained due to the condition of the dehumidifying device, the dehumidifier installed in the system detects the humidity and the dehumidifying device having a spare hollow fiber membrane is installed. The method for treating radioactive gaseous waste according to claim 1, wherein the method is switched. 3. The dehumidifying device is sequentially switched in the case where the dehumidifying device in operation or the system having the dehumidifying device is defective by having a large number of dehumidifying devices containing the spare hollow fiber membranes. The method for treating radioactive gaseous waste according to claim 2. 4. When the dehumidifying device as a whole is defective and the dehumidifying performance cannot be ensured, the humidity is detected by a dew point meter installed in the system and the system is switched to a circulation line to the main condenser. The method of treating radioactive gas waste according to claim 1, wherein the wet gas is prevented from flowing downstream to protect the system.