JP4127580B2 - Treatment method of radioactive gas waste - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radioactive gas waste treatment method improved by a moisture removal method in a dehumidifier.
[0002]
[Prior art]
In general, the coolant of a boiling water reactor is irradiated with neutrons while passing through the core, and a part thereof is decomposed into oxygen and hydrogen, and further, ³ H, ¹⁶ N, ¹⁹ O and the like are generated. Further, radioactive noble gases such as Kr and Xe leak from pinholes or the like generated in the fuel rods, and these noble gases are mixed into the coolant and sent to the turbine system. In addition, there is leakage from outside air to the turbine main condenser.
[0003]
Due to these radioactive gas wastes (hereinafter simply referred to as exhaust gas), turbine systems in boiling water nuclear power plants need to be shielded in the same manner as nuclear reactors to maintain the soundness in and around the plant.
[0004]
By the way, since the exhaust gas is generally non-condensable, it stays in the steam system, particularly in the turbine main condenser. For this reason, conventionally, the exhaust gas staying in the turbine main condenser is extracted by an air extractor and led to an activated carbon type rare gas hold-up tower for processing.
[0005]
FIG. 2 shows an example of a radioactive waste treatment facility installed in a conventional nuclear power plant. Exhaust gas staying inside the turbine main condenser is extracted by the air extractor 1, and the preheater 3 Guided to the hydrogen recombination device 2 composed of the coupler 4 and the exhaust gas condenser 5, hydrogen gas recombination and volume reduction processing are performed.
[0006]
The exhaust gas introduced from the air extractor 1 to the hydrogen recombination device 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 introduced to the downstream recombiner 4. Furthermore, hydrogen and oxygen in the exhaust gas become water vapor by a recombination reaction. Further, in the exhaust gas condenser 5 downstream thereof, the water vapor in the exhaust gas is condensed by the cooling water by the external cooling water to become almost water and separated from the exhaust gas, and the separated water is sent to a turbine main condenser (not shown). Returned.
[0007]
On the other hand, as shown in FIG. 2, the exhaust gas from which moisture has been separated and removed is led to a dehumidifying device 6, and after moisture has been sufficiently removed, is led to an activated carbon type rare gas holdup tower 7. The radioactive gas remaining in the exhaust gas (mainly a rare gas such as Xe or Kr) is adsorbed on the activated carbon, and after a long hold-up, is released from the exhaust tube 9 to the atmosphere by the vacuum pump 8. In FIG. 2, reference numeral 10 denotes an activated carbon type rare gas hold-up tower, 11 denotes an air conditioner, and 12 and 13 denote ducts.
[0008]
These devices are separated into airtight or similar rooms, and each room is air-conditioned. In particular, as shown in FIG. 2, the activated carbon type rare gas holdup tower 10 is air-conditioned from the dedicated air-conditioning equipment 11 through ducts 12 and 13 separately from other general air conditioning, and activated carbon is used to maintain the adsorption performance of the activated carbon. The inside of the noble gas holdup tower inlet pipe 14 can be kept at a constant temperature.
[0009]
FIG. 3 shows details of the conventional dehumidifying device 6 shown in FIG. 2, and the dehumidifying device indicated by reference numeral 16 in FIG. 3 uses a dehumidifying device 16 incorporating a hollow fiber membrane 17 having a large water vapor transmission coefficient. A part of the primary side gas dried by the dehumidifier 16 on the secondary side of the hollow fiber membrane 17 is used for purging, and the secondary side is sucked from the primary side pressure to a low pressure by the vacuum pressure of the main condenser. Thus, a water vapor partial pressure difference is provided between the primary side and the secondary side of the hollow fiber membrane 17 to perform dehumidification.
[0010]
In FIG. 3, reference numeral 18 is a purge gas flow meter, 19 is a purge gas amount adjusting valve, 20 is a purge gas pressure adjusting valve, 21 is a purge gas pressure adjusting outlet valve , 22 is a dehumidifier outlet pressure meter, and 24 is a dehumidifier outlet flow meter. , 25 is a dehumidifier outlet flow rate adjusting valve.
[0011]
[Problems to be solved by the invention]
In the conventional method for treating radioactive gas waste, the vacuum pressure of the main condenser was used as a method of sucking the secondary side of the dehumidifier 16 to a pressure lower than the primary side pressure. There is a problem that the gas waste treatment system cannot be operated when the vacuum pressure of the main condenser cannot be secured. In addition, there is also a problem that the gas waste treatment system cannot be operated alone because the vacuum pressure of the main condenser cannot be secured even during the periodic inspection.
[0012]
The present invention has been made in order to solve the above-mentioned problems, and it is possible to continuously remove moisture in the exhaust gas without using the vacuum pressure of the main condenser, and to obtain a highly reliable radioactive gas. An object is to provide a waste treatment apparatus.
[0013]
[Means for Solving the Problems]
In the present invention, radioactive gas waste generated from a nuclear power plant is led from a main condenser through an air extractor to a hydrogen bonding apparatus to recombine hydrogen gas by a recombiner and volume reduction treatment by an exhaust gas condenser. gastric row, the volume reduction treated after the exhaust gas was removed moisture leading to the dehumidifier incorporating the hollow fiber membranes, the line delay processing leading to the activated carbon ShikiNozomi gas holdup tower Utotomoni, by the dehumidifier In the method for treating radioactive gas waste, in which a part of the dried primary gas is supplied as a purge gas to the secondary side of the hollow fiber membrane, when the vacuum pressure of the main condenser is high, the hollow fiber membrane The secondary exhaust gas is returned to the main condenser, and when the vacuum pressure of the main condenser is low, the secondary exhaust gas is returned to the upstream side of the exhaust gas condenser by a purge vacuum pump .
[0014]
In addition, when a dehumidifying device having a built-in spare hollow fiber membrane is provided in parallel with the dehumidifying device, the humidity is detected by a dew point meter installed in the system outside the dehumidifying device, and the required humidity cannot be obtained. The exhaust gas subjected to the volume reduction treatment is guided to a dehumidifying device incorporating the spare hollow fiber membrane .
[0015]
Furthermore, the state of the dehumidifier detected differential pressure by the installed differential pressure gauge in the system, if the abnormal pressure differential to the system occurs, and the volume reduction process dehumidifier incorporating a hollow fiber membrane of the preliminary It is characterized by guiding exhaust gas .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
In the method for treating radioactive gas waste according to the present invention, the dehumidifier 16a including the hollow fiber membrane 17a having a large water vapor transmission coefficient shown in FIG. 1 is used as the dehumidifier, and the air extractor 1 shown in FIG. And passes through the hollow fiber membrane 17a of the dehumidifier 16a.
[0017]
In this state, a part (for example, 20%) of the primary gas dried by the dehumidifier 16a is used for purging, supplied to the outside of the hollow fiber membrane, and using the purging vacuum pump 38. Suction to a lower pressure than the primary side.
[0018]
Thereby, the water vapor permeation performance is improved by increasing the water vapor partial pressure difference between the primary side and the secondary side of the hollow fiber membrane 17a, 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 through the hollow fiber membrane, and the humidity of the exhaust gas becomes a required percentage or less, for example, 40% or less.
[0019]
Further, the exhaust gas sucked by the purge vacuum pump 38 is returned to the circulation line 40 connected to the upstream side of the condenser so that the gas waste treatment system can be operated independently even when the plant is stopped. .
[0020]
Further, when the humidity of the required percentage or less cannot be obtained due to the state of the dehumidifying device 16a, the humidity is detected by a dew point meter installed in the system, and the dehumidifying device 16b incorporating the spare hollow fiber membrane 17b is switched to. As a result, the dehumidifying performance can be secured.
[0021]
In addition, when the differential pressure increases or decreases depending on the state of the dehumidifying device, the differential pressure is detected by a differential pressure gauge installed in the system, and dehumidifying performance can be ensured by switching to a dehumidifying device incorporating a spare hollow fiber membrane. It becomes like this.
[0022]
An embodiment of a method for treating radioactive gas waste according to the present invention will be described with reference to FIGS.
FIG. 1 shows a configuration around a dehumidifier 16 (16a, 16b) in an exhaust gas treatment device. In the figure, the dehumidifiers 16a, 16b are connected to dehumidifier inlet valves 31a, 31b and dehumidifier outlet valves 32a, 32b. They are connected in parallel, and only one system is processed during normal operation.
[0023]
The wet exhaust gas to be treated (temperature: 40 ° C., dew point: 100%, pressure: 0.8ata) flows from the exhaust gas condenser 5 into the dehumidifiers 16a, 16b. As shown in FIG. 1, hollow fiber membranes 17a and 17b having a large water vapor transmission coefficient are attached to the dehumidifiers 16a and 16b, respectively, and the exhaust gas sucked by the purge vacuum pump 38 is supplied to the hollow fiber membranes 17a. , 17b.
[0024]
During operation with the dehumidifier 16a system, the temperature of the exhaust gas is measured by the dehumidifier outlet dew point meter 23. If the temperature exceeds the allowable dew point of the system (for example, −20 ° C.), an alarm is issued or the dehumidifier a The inlet valve 31a and the outlet valve 32a are closed, the dehumidifier inlet valve 31b and the outlet valve 32b are opened, and the operation number is switched to prevent the humid exhaust gas from flowing into the activated carbon rare gas hold-up device.
[0025]
In addition, when the pressure of the system is measured by the condenser outlet pressure gauge 27 and becomes equal to or higher than the system operation setting pressure (for example, atmospheric pressure), the condenser outlet circulation water line valve 29 is opened to open the condenser outlet circulation line. By adjusting the pressure regulating valve 30, the system pressure is set within the set value.
[0026]
In addition, the dehumidifier inlet flow meter 28 ensures a flow rate suitable for the processing amount of each of the dehumidifiers 16a and 16b by adjusting the dehumidifier inlet flow rate adjustment valve 19, thereby performing stable operation of the system.
[0027]
As shown in FIG. 1, the inside of each dehumidifier 16a, 16b is a part of the primary gas dried by the dehumidifier 16a, 16b (for example, 20%) for purging, and the purge gas amount is dehumidified from the purge gas flow meter 18. An amount corresponding to about 20% of the exhaust gas treatment amount measured by the apparatus inlet flow meter 28 is secured by adjusting the purge gas amount adjusting valve 20.
[0028]
In addition, the pressure of the purge gas is adjusted by the purge gas pressure adjustment valve 20 according to the set pressure of the purge gas pressure gauge 36, while the plant is in operation by the main condenser, and when the plant is stopped by the purge vacuum pump 36, Suction is performed at a lower pressure than the primary side.
[0029]
The exhaust gas sucked by the purge vacuum pump is circulated upstream of the exhaust gas condenser 5 through the circulation line 40, so that the off-gas (OG) system can be operated independently even when the plant is stopped.
[0030]
As a result, the water vapor content in the exhaust gas flowing through the hollow fiber membranes 17a and 17b passes through the hollow fiber membranes 17a and 17b to be separated and removed, and the relative humidity of the exhaust gas becomes a required percentage, for example, approximately 40% or less. It is like that. This is because the exhaust gas supplied to the activated carbon rare gas holdup tower 7 needs to have a relative humidity of 40% or less.
[0031]
The purge gas can be selected by switching the purge gas inlet valves 34a and 34b and the purge gas outlet valves 35a and 35b with respect to the operating system of the processing apparatus.
[0032]
Next, the moisture removal method in each dehumidifier 16a, 16b is demonstrated.
In FIG. 1, assuming that the system on the dehumidifying device 16a side is in operation, steam is cooled by the condenser 5, and the condensed exhaust gas is discharged by a vacuum pump 8 (see FIG. 2) that sucks the system. It is guided to the dehumidifier 16a via the dehumidifier inlet valve 31a and passes through the hollow fiber membrane 17a.
[0033]
At this time, the inside of the dehumidifying device 16a is adjusted to an appropriate flow rate by the purge gas amount adjusting valve 19 inside the dehumidifying device 16a, and the purge gas is caused to flow into the dehumidifying device 16a through the purge gas inlet valve 34a to improve the water vapor permeability. .
[0034]
Further, in order to evacuate the inside of the dehumidifier 16a and maintain it at a pressure lower than the pressure of the primary system, the purge vacuum pump 38 is used, and the set value of the purge gas pressure gauge 36 is set via the purge gas outlet valve 35a. The pressure is adjusted by the purge gas pressure adjustment valve 20. As a result, appropriate vacuuming is performed, so that the water vapor content in the exhaust gas flowing through the hollow fiber membrane 17a is removed through the hollow fiber membrane 17a and returned to the upstream side of the turbine main condenser via the circulation line 40. It is.
[0035]
For this reason, the exhaust gas after passing through the dehumidifier 16a has a relative humidity of a required percentage, for example, 40% or less, and enters the activated carbon type rare gas holdup tower 7 (see FIG. 2) via the dehumidifier outlet valve 32a. Guided and delayed.
[0036]
When trouble occurs in the dehumidifier 16a and the dew point meter 23 at the outlet of the dehumidifier 16a becomes larger than the set value, the dehumidifier inlet valve 31a, the dehumidifier outlet valve 32a, the purge gas inlet valve 34a, and the purge gas outlet valve 35a Is closed. At the same time, the dehumidifier inlet valve 31b, the dehumidifier outlet valve 32b, the purge gas inlet valve 34b, and the purge gas outlet valve 35b are opened, and the system is switched to the dehumidifier 16b side.
[0037]
Further, when trouble or the like occurs in the dehumidifier 16a and the differential pressure gauge 33 of the dehumidifier 16a deviates from the allowable value, the dehumidifier inlet valve 31a, the dehumidifier outlet valve 32a, the purge gas inlet valve 34a, and the purge gas outlet valve 35a are Closed. At the same time, the dehumidifier inlet valve 31b, the dehumidifier outlet valve 32b, the purge gas inlet valve 34b, and the purge gas outlet valve 35b are opened, and the system is switched to the dehumidifier 16b side.
[0038]
【The invention's effect】
According to the present invention, the operation of the exhaust gas system can be performed at the time of starting and stopping the plant and during a period in which the vacuum of the turbine main condenser cannot be secured during the plant stop. In addition, air that is not dehumidified during operation during regular inspections will not flow into the rare gas hold-up system.
[Brief description of the drawings]
FIG. 1 is a system diagram showing the periphery of a dehumidifying device for explaining an embodiment of a method for treating a radioactive gas waste according to the present invention.
FIG. 2 is a system diagram showing a conventional radioactive gas waste treatment facility.
3 is a system diagram showing the periphery of the dehumidification tower in FIG. 2. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Air extractor, 2 ... Hydrogen recombination device, 3 ... Exhaust gas preheater, 4 ... Exhaust gas recombiner, 5 ... Exhaust gas condenser, 6 ... Dehumidifier, 7 ... Activated carbon type rare gas holdup tower, 8 ... Vacuum pump, 9 ... Exhaust tube, 10 ... Activated carbon type rare gas holdup tower room, 11 ... Air conditioning equipment, 12, 13 ... Duct, 14 ... Activated carbon type rare gas holdup tower inlet piping, 15 ... Dehumidifier inlet flow adjustment valve , 16, 16a, 16b ... dehumidifier, 17, 17a, 17b ... hollow fiber membrane, 18 ... purge gas flow meter, 19 ... purge gas amount adjusting valve, 20 ... purge gas pressure regulating valve 21 ... purge gas pressure regulating Seide port valve, 22 ... Dehumidifier outlet pressure gauge, 23 ... Dehumidifier outlet dew point meter, 24 ... Dehumidifier outlet flow meter, 25 ... Dehumidifier outlet flow control valve, 26 ... Condenser outlet thermometer, 27 ... Condenser outlet pressure gauge 28 ... Dehumidifier inlet flow meter, 29 ... Condenser outlet circulation line valve, 30 ... Condenser outlet circulation line Pressure regulating valve, 31 ... Dehumidifier inlet valve, 32 ... Dehumidifier outlet valve, 33 ... Dehumidifier differential pressure gauge, 34 ... Purge gas inlet valve, 35 ... Purge gas outlet valve, 36 ... Purge gas pressure gauge, 37 ... Purge vacuum pump inlet Valve: 38 ... Purge vacuum pump, 39 ... Purge vacuum pump outlet check valve, 40 ... Circulation line.

Claims (4)

Radioactive gaseous waste generated from nuclear power plants, have rows volume reduction process by recombination and the exhaust gas condenser of hydrogen gas by recombiner led to hydrogen bonding device through the air ejector from main condenser, the volume reduction treated after the exhaust gas was removed moisture leading to the dehumidifier incorporating the hollow fiber membranes, activated carbon ShikiNozomi gas holdup line delay processing leading to tower Utotomoni primary which is dried by the dehumidifier In the method for treating radioactive gas waste, which supplies a part of the side gas as a purge gas to the secondary side of the hollow fiber membrane ,
When the vacuum pressure of the main condenser is high, the secondary side exhaust gas of the hollow fiber membrane is returned to the main condenser, and when the vacuum pressure of the main condenser is low, the secondary side exhaust gas is purged vacuum A method for treating radioactive gas waste, wherein the waste gas is returned to the upstream side of the exhaust gas condenser by a pump . When a dehumidifying device having a built-in spare hollow fiber membrane is provided in parallel with the dehumidifying device, the humidity is detected by a dew point meter installed in a system outside the dehumidifying device, and when the required humidity cannot be obtained, The method for treating a radioactive gas waste according to claim 1 , wherein the exhaust gas subjected to the volume reduction treatment is guided to a dehumidifying device incorporating a hollow fiber membrane . Wherein the state of the dehumidifier detects humidity by the installed hygrometer in the system, according to claim 1 the relative humidity of the radioactive gas waste and adjusting the amount of the purge gas to a predetermined range or 2. A method for treating radioactive gas waste according to item 2. When the differential pressure is detected by a differential pressure gauge installed in the system to determine the state of the dehumidifier, and a differential pressure abnormality occurs in the system, the volume-reduced exhaust gas is added to the dehumidifier having the spare hollow fiber membrane built therein. The method for treating a radioactive gas waste according to claim 2 or 3, wherein the radioactive gas waste is treated.

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