JPH0560079B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for treating radioactive gaseous waste in a nuclear power plant.

[Technical Field of the Invention] Gas extracted from the turbine main condenser of a boiling water nuclear power plant or gas degassed from the primary coolant of a pressurized water nuclear power plant contains radioactive substances such as rare gases. Therefore, it is necessary to provide equipment to safely dispose of these substances. For this reason, all of the above-mentioned gases are treated by recombining the hydrogen and oxygen contained therein, followed by dehumidifying and drying the exhaust gas, and then performing rare gas adsorption treatment using an activated carbon rare gas hold up tower under low humidity. It has become common to dissipate from the rear exhaust tower.

This device is a radioactive gas waste treatment device.

Hereinafter, a method for disposing of radioactive gaseous waste will be described in detail using a boiling water nuclear power plant among light water nuclear reactors as an example.

The coolant of a boiling water reactor is exposed to neutron irradiation while passing through the reactor core with a high neutron flux, and a portion of it decomposes not only into oxygen and hydrogen, but also into ³ H, ¹⁶ N, and ¹⁹ O.
etc. occur. In addition, radioactive rare gases such as Kr and Xe leak from pinholes formed in the fuel rods.
These are mixed with steam and sent to the turbine system. In addition to this, there is also leakage of outside air into the turbine main condenser.

Due to these radioactive gaseous wastes (hereinafter simply referred to as exhaust gas), the turbine system in a boiling water nuclear power plant must be equipped with shielding equipment similar to that of a nuclear reactor to maintain the health of the plant and its surroundings.

However, since the exhaust gas is generally non-condensable, it remains within the steam system, particularly within the turbine main condenser.

Therefore, an air extractor is connected inside the turbine main condenser, and the exhaust gas retained here is guided to an activated carbon type rare gas holding up tower for treatment.

This processing device is configured as follows.

That is, as shown in FIG.
Bleed air out of the turbine system. The exhaust gas extracted to the outside of the system is preheated in the preheater 3 to a temperature at which the oxygen and hydrogen contained therein are efficiently recombined, and then guided to the downstream recombiner 4 where it is heated. The hydrogen and oxygen contained in the exhaust gas recombine to form water vapor. Furthermore, in the condenser 5 downstream of the condenser 5, most of the water vapor in the exhaust gas becomes water due to the cooling effect of external cooling water, the exhaust gas is separated, and the water is returned to the turbine main condenser 1.

After that, the exhaust gas passes through a dehumidifier 6 and a dryer 7a or 7b, and after sufficiently removing moisture, it is led to activated carbon rare gas hold-up towers 8, 8, 8, where the remaining radioactivity (mainly X , Kr, and other noble gases) are adsorbed onto activated carbon, and after a long hold-up, they are released into the atmosphere from an exhaust stack 10 via a vacuum pump 9.

By the way, the exhaust gas flowing into the dehumidifier 6 has a temperature of 10°C.
It is cooled to a non-freezing temperature below 0°C and above 0°C, for example, about 5°C, and reaches a dryer 7 (indicated by 7a) via a pipe 11a. Whether the dryer 7a uses a dehumidifier or a freeze dryer, one additional dryer 7b is installed as a backup when performing regeneration operation, and the two dryers 7a and 7b are always used alternately. I'm driving. This dryer 7a, 7
From b, the exhaust gas, which has been dried to a dew point of -20° C. and has a sufficiently low absolute humidity, flows to the activated carbon rare gas holding up tower 8. Activated carbon rare gas hold up tower 8
In order to remove the decay heat associated with the attenuation of rare gases in activated carbon, the temperature is adjusted to, for example, 1°C in winter and 20°C in summer. Here, when the temperature flowing into the activated carbon rare gas hold up tower 8 is 1°C, the relative humidity of the exhaust gas is about 19%, and when it is 20°C, it is about 5%. FIG. 5 is a psychrometric diagram showing the treatment temperature t and humidity conditions of the gaseous waste treatment system. In FIG. 5, the line between A and B shows the range of exhaust gas temperature and humidity in a conventional activated carbon type rare gas holding up tower on a psychrometric diagram.

[Problems with the Background Art] Conventionally, as mentioned above, a decrease in the dynamic adsorption coefficient has been prevented by sufficiently reducing the absolute humidity in the exhaust gas, so it is necessary to perform alternate operation in the dryer 7. However, since high reliability is required for equipment in nuclear power plants, it is desirable to avoid alternate operation as much as possible, and there is room for some improvement.

In addition, the dehumidifier 6 performs direct cooling with a fluorocarbon cooling device or indirect cooling with a fluorocarbon cooling device, brine pump, and brine tank, and since both have dynamic equipment such as a fluorocarbon compressor and brine pump, There was some room for improvement in order to increase reliability.

FIG. 3 shows the relationship between the moisture content of activated carbon and the relative humidity of the treated gas. As is clear from this figure, when the relative humidity of the treated gas exceeds 40%, the moisture content of activated carbon rapidly increases to over 20%. It is known that this increase in water content reduces the adsorption capacity of activated carbon for rare gases. FIG. 4 is a characteristic diagram showing the relationship between the moisture content of activated carbon and the dynamic adsorption coefficient for Xe.
From this figure, it can be seen that the dynamic adsorption coefficient decreases rapidly when the water content approaches 20%.

As shown in Figures 3 and 4, even if the absolute humidity of exhaust gas is not significantly reduced in rare gas treatment of activated carbon, if we focus on the relative humidity of exhaust gas and keep it below 40%, the Effective treatment can be performed with almost no reduction in target adsorption coefficient.

On the other hand, it is known that when a rare gas is adsorbed using activated carbon, the dynamic adsorption coefficient decreases as the treatment temperature increases. FIG. 2 shows an example of the value of the dynamic adsorption coefficient K [cm ³ /g] for Xe and Kr with respect to temperature conditions.

Based on these conditions, the relative temperature is 40%
The following shows that it is desirable for the temperature to be as low as possible within the economical control range of air conditioning, and by comprehensively evaluating these factors, there is a need for a radioactive gas waste treatment system that has a highly reliable and inexpensive configuration. .

[Purpose of the Invention] The present invention has been made to satisfy the above-mentioned needs, and is a method for continuously flowing exhaust gas with a relative humidity of 40% or less without increasing the processing control temperature in an activated carbon rare gas hold up tower. The object of the present invention is to provide a radioactive gas waste treatment device that is capable of performing the same operations and has higher reliability by reducing the number of dynamic devices as much as possible.

[Summary of the invention] The present invention cools the radioactive exhaust gas generated from a nuclear power plant to a non-freezing temperature of 10°C to 0°C, and immediately installs an activated carbon rare gas holding up tower downstream of a dehumidifier that dehumidifies and cools the radioactive exhaust gas. Actual humidity of exhaust gas, i.e. 7.63 [g/Kg] at 10℃
By heating the exhaust gas and injecting dry air to reduce the relative humidity to 40% or less, air with a moisture content of
Exhaust gas is continuously treated.

That is, in the method for treating radioactive gaseous waste of the present invention, radioactive gaseous waste generated from a nuclear power plant is cooled to a temperature between 0°C and 10°C in a dehumidifier, and the waste that has passed through the dehumidifier is cooled. Dry gas whose absolute humidity is lower than the exhaust gas is added to and mixed with the radioactive gas waste whose relative humidity is 100% at the outlet, and the mixture is transferred to an activated carbon rare gas old up tower at a relative humidity of 40% or less and a temperature of 100°C or less. It is characterized by attenuating radioactivity using the activated carbon type rare gas old up tower.

The temperature of the exhaust gas can be increased by adjusting the temperature of the air in the room where the activated carbon rare gas hold up tower is installed and by heating the activated carbon rare gas hold up tower and its inlet piping, or by installing a separate small heater. This can also be done by Also,
Injection of dry air can be carried out by connecting the instrumentation air piping from the dehumidifier to the piping of the activated carbon rare gas hold up tower via a valve.

[Embodiments of the Invention] (Structure of the Embodiments) Hereinafter, embodiments of the present invention will be described with reference to FIG. Note that the same parts in FIG. 1 as in FIG. 7 are given the same reference numerals, and the explanation of the overlapping parts will be omitted.

That is, in FIG. 1, the exhaust gas flowing out of the dehumidifier 50 flows into the activated carbon rare gas holding up tower 8 through the pipe 13. The activated carbon rare gas hold up tower 8 is installed in a chamber 21 that is airtight or nearly airtight. A suction duct 23 and a discharge duct 24 connected to an air conditioner 22 are installed in the room 21 . The dehumidifier 50 uses cold water (5°C to 7°C) for air conditioning, etc. installed in the power plant.
It is a heat exchanger and static device that cools the exhaust gas at a temperature of about 30°F (°C). A flow meter 14 is installed in the pipe immediately after the cooler outlet.
Thermometer 15, or pressure gauge 1 if necessary
Measuring instruments such as 6 are provided. Measurement information from these measuring instruments is connected to a computer 17. In addition, new dry air from the instrumentation air system is injected from the pipe 26 via the control valve 25 into the piping leading to the activated carbon rare gas hold up tower 8 after the installation of these measuring instruments. Additional mixing is performed, and the flow rate is controlled by the control valve 25 by the computer 17.

However, the exhaust gas is cooled down to 10° C. or lower in the dehumidifier 50. On the other hand, since the inside of the chamber 21 housing the activated carbon rare gas hold up tower 8 is heated and maintained at 20°C by the air conditioning equipment 22, the rare gas hold up tower 8 is also indirectly heated to 20°C. has been done. The exhaust gas is heated to 20°C while flowing through pipe 13, and further heated to 20°C from pipe 26.
A certain amount of fresh dry air is additionally mixed to increase the flow rate and flow to the activated carbon rare gas hold up tower 8. The pipes 13 and 26 are installed in the chamber 21 so as to have a length sufficient to stabilize the gas therein at around the control temperature, if necessary.

The relative humidity of the exhaust gas is less than 40% at the entrance of the activated carbon rare gas hold up tower, and the temperature is approximately 20°C.An example of this process will be explained numerically.

If the exhaust gas in pipe 13 with a flow rate of 40Nm ³ /h reaches 20℃ due to temperature rise before the dry air injection part, the dew point
Exhaust gas (air containing trace amounts of radioactive rare gases, etc.) at 10°C has a relative humidity of 52%. This condition is indicated by a dot A on the psychrometric diagram in FIG. On the other hand, the instrumentation air to be injected is dry air with a dew point of -40°C, and the relative humidity is approximately 3% at 20°C. This state is point B in the figure. Here, for the exhaust gas flow rate of 40m ³ /h, the dry air injection rate is 10m ³ /h, 20
m ³ /h, 30m ³ /h, and 40m ³ /h, the relative humidity of the mixed gas can be calculated as 43%, 36%, 31%, and 21%, respectively.

Point C in Figure 5 shows the result when the flow rate of dry air is set to 20Nm ³ /h by the computer 17 and the control valve 25 to obtain a mixed gas state with a set relative humidity of 36%. This is the point that divides the line segment connecting point A and point B on the diagram into a 20:40 ratio.

In this way, at a temperature of 20℃, the target
The exhaust gas, which had a relative humidity of 52%, which is less than 40%, can be easily reduced by 36% by the present invention, to the extent that it does not adversely affect the dynamic adsorption coefficient of activated carbon for rare gases. By adopting such a system, the relative humidity of the exhaust gas can be lowered to a level that does not affect the activated carbon in any way, without having to perform alternate operation like the conventional dryers 7a and 7b shown in Fig. 7. I can do it.

By the way, the dynamic adsorption coefficient K used in the above explanation
[cm ³ /g] is a value commonly used to calculate the required amount of activated carbon, and it is calculated based on the exhaust gas flow rate F.
The following relational expression exists between [m ³ /hr], the required amount M [ton] of activated carbon, and the hold-up time T [hr].

T=K・M/F ……(1) Therefore, if the dynamic adsorption coefficient K is high and the exhaust gas flow rate F is low, the required amount of activated carbon will be smaller, which will improve economic efficiency. It is advantageous in this respect.
In the above explanation example of relative humidity calculation, the relative humidity is decreased from 52% to 36% to increase the dynamic adsorption coefficient, and therefore the flow rate of activated carbon increases from 40 m ³ /h to 60 m ³ /h. There are opposing effects on requirements. Therefore, if the amount of dry air injection is increased to lower the relative humidity, the dynamic adsorption coefficient will increase, but on the other hand, the influence of the relative humidity will be greater40.
It has the effect of reducing the required amount of activated carbon at a point where it exceeds around % or less.

In addition, newly injecting more dry air than necessary increases the flow rate F and conversely increases the required amount of activated carbon, which is an undesirable result. In other words, when injecting and mixing dry air, there is an optimum amount, and the calculation by the computer 17 obtains this optimum value.

Comparing the treatment conditions for activated carbon in a conventional gaseous waste treatment system and the same treatment conditions in the present invention,
Despite adverse conditions such as temperature and relative humidity, the dynamic adsorption coefficient of the present invention decreases slightly, and when the worsening conditions due to increased flow rate are combined, the required amount of activated carbon is 1.4.
It will be about 2.1 times to 2.1 times.

However, the present invention eliminates the need for switching operation in the conventional dryer, improving operational reliability, and also has a significant cost reduction effect by eliminating the dryer and its peripheral equipment, thereby reducing the cost increase due to the increase in the amount of activated carbon required. It is possible to provide a device that fully compensates for this and is cheaper than the conventional one. Additionally, dehumidifiers can eliminate dynamic equipment such as conventional fluorocarbon cooling equipment, reducing equipment costs and building space, and further improving reliability.

The present invention determines the required amount M of activated carbon from the design maximum exhaust gas flow rate F, hold-up time T, and dynamic adsorption coefficient K using the above-mentioned relational expression 1. In this case, it may be possible to reduce operating costs by omitting dry air injection during normal operation when the exhaust gas flow rate is considerably lower than the design maximum value. For this reason, even when the exhaust gas relative humidity is high and the dynamic adsorption coefficient is low, the flow rate F in relational formula 1 is small, so the calculated value of the required amount of activated carbon is less than the required amount M calculated based on the maximum exhaust gas flow rate. This is a possible driving method if the vehicle is turned downward.

It is also possible to inject appropriately heated dry air so that the average temperature of the exhaust gas after injecting the dry air easily rises to the specified treatment temperature.

Furthermore, the dry air control valve 25 can also be used to manually control the flow rate based on worst-case conditions.

FIG. 6 shows another embodiment of the present invention, in which the same parts as those in FIG. This is a case where an ejector 27 driven by compressed air for each layer is used instead of a vacuum pump as the drive source of the system described in . In this embodiment, since the relative humidity of the exhaust gas sent to the exhaust stack is very low, a portion of the exhaust gas can be returned by the control valve 25 and used for lowering the relative humidity and re-adsorbing radioactive materials.

[Effects of the Invention] As described above, according to the present invention, exhaust gas with a relative humidity of 40% or less can be continuously flowed through a rational system configuration, and there is no need to switch the dryer as in the past. It becomes necessary.

Additionally, by removing the dehumidifier cooling device, dynamic equipment can be eliminated, so the operational reliability of the entire device can be significantly improved.

Furthermore, not only can you reduce the number of dryers and their peripheral equipment, but you can also reduce the number of cooling devices for dehumidification.
It is possible to achieve significant simplification and cost reduction of the equipment.

In the embodiments of the present invention, a boiling water type nuclear power plant has been described, but the present invention is not limited to this, and can of course be applied to a pressurized water type nuclear power plant, a fast breeder reactor plant, etc.

In other words, the gas degassed from the primary coolant of a pressurized water reactor also contains radioactive noble gases.
The present invention can be applied to the case where activated carbon is used as this treatment method. In this case, the precooler/activated carbon type rare gas holding up tower according to the present invention is provided downstream from where the primary cooling water is degassed.

Furthermore, the present invention can be applied to the treatment of radioactive gaseous waste in other furnace types as well. For example, in a new type converter reactor, it can be applied to the exhaust gas extracted from the turbine main condenser as in a boiling water reactor plant.

Furthermore, in particular, not only the exhaust gas from the furnace body, but also
The present invention can also be applied to the treatment of exhaust gas generated in conjunction with this. For example, this includes exhaust gas from the primary argon gas system, fuel handling and storage system, equipment mounted on top of the reactor, etc. in a fast breeder reactor. In addition, the same applies to vent gas from the waste liquid tank of the radioactive liquid waste treatment system.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing an embodiment of the radioactive gas waste treatment apparatus according to the present invention, Fig. 2 is a characteristic diagram showing the relationship between the dynamic adsorption coefficient of activated carbon for rare gases and temperature, and Fig. 3 is a diagram showing the relationship between the temperature and the dynamic adsorption coefficient of activated carbon for rare gases. Figure 4 is a characteristic diagram showing the relationship between the relative humidity of activated carbon and the moisture content of activated carbon, Figure 4 is a characteristic diagram showing the relationship between the moisture content of activated carbon and the dynamic adsorption coefficient for rare gases, and Figure 5 is a graph showing the relationship between the moisture content of activated carbon and the dynamic adsorption coefficient for rare gases. FIG. 6 is a system diagram showing another embodiment of the present invention. FIG. 7 is a system diagram showing a conventional radioactive gas waste processing apparatus. 1...Turbine main condenser, 2...Air extractor,
3... Preheater, 4... Recombiner, 5... Condenser,
6... Dehumidifier, 7a, 7b... Dryer, 8... Activated carbon rare gas hold up tower, 9... Vacuum pump, 10... Exhaust pipe, 13... Piping, 14... Flow meter, 15... ...Thermometer, 16...Pressure gauge, 17...
...Calculating machine, 21...Room, 22...Air conditioning equipment, 23
...Suction duct, 24...Discharge duct, 25...
Control valve, 26...Piping, 27...Ejector, 5
0...Dehumidifier.

Claims (1)

[Claims] 1 Radioactive gaseous waste generated from nuclear power plants is cooled to a temperature between 0℃ and 10℃ using a dehumidifier,
Relative humidity at the outlet of the dehumidifier passing through the dehumidifier
Adding and mixing dry gas whose absolute humidity is lower than the exhaust gas to the radioactive gaseous waste that has become 100%,
1. A method for treating radioactive gaseous waste, which comprises introducing the waste into an activated carbon rare gas old up tower at a relative humidity of 40% or less and a temperature of 100° C. or less, and attenuating radioactivity in the activated carbon rare gas old up tower.