JPS5815078B2 - Radioactive waste gas treatment equipment - Google Patents

Description

[Detailed description of the invention] A radioactive waste gas treatment device in a nuclear power plant is
Conventionally, the same amount of gas was kept in a storage tank for a certain period of time and then released after the radioactivity had sufficiently decayed.

However, recently, with the aim of further reducing the amount released, hydrogen gas is continuously purged to extract radioactive rare gases (Kr, Xe) into the volume control tank of the chemical volume control system, and the generated radioactive rare gases are included. A method of concentrating and reducing the volume of the radioactive rare gas by separating only hydrogen from the hydrogen gas and storing it in a storage tank for a long period of time is increasingly being adopted.

As one type of treatment equipment for hydrogen gas containing this radioactive rare gas, conventional waste gas treatment systems employ a hydrogen separation method that utilizes the property of a palladium alloy membrane to selectively permeate only hydrogen and prevent all other gases from permeating. better known.

This conventional system is as shown in Figure 1, in which a hydrogen gas containing a trace amount of radioactive rare gas purged from a volume control tank 1 is passed through a palladium alloy membrane together with hydrogen gas recirculated from a storage tank 2. It is fed under pressure to the used hydrogen separator 3 (hereinafter referred to as hydrogen separator), and a portion of the hydrogen is separated.

After this part of the hydrogen has been separated, the hydrogen gas containing a small amount of radioactive rare gas is transferred to the pressure control valve 4 at the outlet of the hydrogen separation device 3.
The partially separated hydrogen is sent to storage tank 2 through
Since the hydrogen is pure hydrogen due to the hydrogen permselectivity of the palladium alloy membrane, it is reused as hydrogen for purging the volume control tank 1.

However, the disadvantage of the above system is that the hydrogen amount gas processed by the hydrogen separator 3 is sent to the storage tank 2 and then recirculated to the hydrogen separator 3, and the installed capacity is reduced from the volume control tank 1 that should originally be processed. The amount of purge gas was significantly larger than the amount of purge gas in storage tank 2, and storage tank 2 must be filled with hydrogen before starting operation. Due to the accumulation, the hydrogen concentration in the hydrogen gas to be processed by the hydrogen separation device 3 decreases, and when a predetermined amount of separated hydrogen is required for a long period of time, a very large membrane area of the palladium alloy membrane is required. .

That is, equipment with a considerably larger capacity was required compared to the amount of purge gas from the volume control tank 1 to be treated.

Furthermore, in order to obtain a predetermined amount of separated hydrogen over a long period of time, it was necessary to increase the area of the palladium alloy membrane more than necessary.

As is well known, palladium is a precious metal and is expensive, so it is economically disadvantageous to use a large amount of it.

Furthermore, since the storage tank 2 must be filled with hydrogen before the start of operation, this entire facility contains a considerable amount of hydrogen, which is very disadvantageous from an explosion-proofing point of view.

In addition, in the figure, 5 is a compressor, 6 is a pressure control valve, and 7 is a compressor.

As mentioned above, the reason why the conventional system had to recirculate hydrogen gas from the storage tank 2 is that if it is not recirculated, the waste gas (extremely concentrated Therefore, the flow rate of the bleed gas (hereinafter referred to as bleed gas) becomes extremely small, and the pressure control valve 4 of the hydrogen separation device 3 output line has to meet very special requirements [specifically, the required Cu (valve capacity) The value was extremely low, and there was nothing on the market that met this requirement.

That is, the amount of radioactive rare gas contained in the waste gas from the volume control tank 1 is extremely small, and most of it is hydrogen.

Therefore, the flow rate of the bleed gas after most of the hydrogen has been separated in the hydrogen separator 3 is extremely small, and the required Cu value of the pressure control valve under this flow rate is about 10-8. There were no pressure control valves with a small Cu value on the market.

Furthermore, due to recirculation, the storage tank 2 must be filled with pure hydrogen before the start of operation, so the amount of hydrogen held in this facility as a whole has increased dramatically, especially for the storage tank 2. Although explosion-proof measures were extremely difficult,
If the bleed gas is highly concentrated and has a minimal flow rate, there is no need to circulate the hydrogen in the tank, so if it is filled with an inert gas such as helium, it can be completely explosion-proof.

The present invention was proposed in order to eliminate the above-mentioned conventional drawbacks.The present invention uses hydrogen as a carrier gas, and deposits a palladium alloy film into a container filled with a gas to be treated containing a small amount of radioactive rare gas through an outlet pipe. A hydrogen separation device to be used is connected, a vacuum pump is connected to the separation hole of the hydrogen separation device via a first switching valve, and a storage tank is connected to the outlet of the separation device via a micro flow rate fluid pressure control device. Moreover, by communicating the outlet pipe and the storage tank through a second switching valve, it is possible to provide a radioactive waste gas processing device that does not require recirculation of hydrogen gas from the storage tank as in conventional systems. It is something to do.

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2, by continuously purging hydrogen into the volume control tank 8, radioactive rare gases (Kr, Xe,
), etc. are extracted into hydrogen gas, and the hydrogen gas containing extremely small amounts of radioactive rare gas, etc. is pressurized by the compressor 9 to a predetermined pressure necessary for hydrogen separation, and then is sent under pressure to the hydrogen separation device 10.

; In the hydrogen separator 10, most hydrogen is separated under predetermined pressure and temperature conditions due to the property of the palladium alloy membrane that selectively permeates only hydrogen and does not permeate any other gases.

Since the amount of radiation and rare gas originally extracted from the primary coolant in the volume control tank 8 is very small, the remaining waste gas (bleed gas) after most of the hydrogen has been separated is very small. It is in an extremely concentrated state, and a micro flow rate fluid pressure control device 11 is provided to ensure a predetermined pressure under extremely low flow rates.

The bleed gas is controlled by the pressure control device 1 under this extremely small flow rate.
1, and is sent to a storage tank 12 filled with an inert gas such as helium before the start of operation, where it is stored for a long period of time.

On the other hand, most of the separated hydrogen (which is pure hydrogen due to the hydrogen permselectivity of the palladium alloy membrane) is reused as hydrogen for purging the volume control tank 8 after being pressurized to a predetermined pressure by the compressor 13. .

The storage tank 12 can be stored for a long period of time without being released during the life of the plant, with a tank capacity within a practical range, and even if a very small amount of unseparated hydrogen is accumulated in the bleed gas, It is now possible to keep the temperature below the explosive limit for up to two years.

In addition, when the hydrogen concentration in the storage tank 12 approaches the explosive limit, the purge line from the volume control tank 8 is closed, and the waste gas in the storage tank 12 is circulated to the hydrogen separation device 10 to prevent hydrogen permeation. By evacuating the side with the vacuum pump 14, hydrogen can be removed.

In this case, since the flow rate of the bleed gas increases, the pressure of the bleed gas is controlled by the pressure control valve 15.

In other words, in the lineup during normal operation, there are branch valves 16 and 17.
, 18 are opened, and the branch valves 19, 20, 21 are closed.

However, in the lineup during hydrogen removal operation in the storage tank 12, on the contrary, the branch valves 16, 17, and 18 are closed, and the branch valves 19, 20, and 21 are opened.

As explained in detail above, the present invention uses hydrogen as a carrier gas and connects a hydrogen separation device using a palladium alloy membrane to a container filled with a gas to be treated containing a small amount of radioactive rare gas through an outlet pipe. The separation efficiency (hydrogen permeation efficiency) of the palladium alloy membrane depends on the hydrogen partial pressure difference on both sides of the membrane. is the key point.

That is, since the amount of radioactive rare gas is extremely small, pressure control becomes extremely difficult.

In the present invention, the pressure control device performs pressure control while retaining a trace amount of rare gas in a concentrated form without hydrogen, thereby obtaining rare gas containing almost no hydrogen gas.

In addition, a second switching valve is interposed in the pipe connecting the container and the hydrogen separation device, and hydrogen gas is not recirculated from the storage tank as in the past, so radioactive rare gas is not accumulated in the storage tank. Since there is no change in the hydrogen concentration at the inlet of the hydrogen separator, constant hydrogen separation performance can be obtained over long periods of operation.

In addition, a vacuum pump is connected to the separation hole of the hydrogen separator through the first switching valve, so even if the hydrogen concentration in the storage tank approaches the explosive limit, if you use this vacuum pump, the hydrogen in the storage tank can be transferred to the hydrogen separator. The danger of explosion can be easily prevented as it can be removed by

Furthermore, by filling the storage tank with an inert gas such as helium before starting operation, even if a very small amount of unseparated hydrogen in the bleed gas accumulates, the hydrogen concentration remains below the explosive limit for a long period of time. It can be held down to

Therefore, according to the present invention, the concentration of radioactive noble gas in the primary coolant is reduced, and the amount of radioactive noble gas ultimately released from the plant can be greatly reduced, and it is highly concentrated with a smaller palladium alloy membrane area than before. Not only can volume reduction be achieved, but waste gas can also be treated with more economical equipment capacity than before.

Note that if the capacity of the storage tank is appropriately selected within a feasible range, it is possible to store the radioactive rare gas for a long period of time without releasing it during the life of the plant.

The present invention can be effectively applied to radioactive waste gas treatment equipment for nuclear power plants.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an example of a conventional radioactive waste gas processing apparatus, and FIG. 2 is a system diagram of a radioactive waste gas processing apparatus showing an embodiment of the present invention. Explanation of the main parts of the figure, 8...Volume control tank (
container), 10...hydrogen separation device, 11...
...Minor flow rate fluid pressure control device, 12...Storage tank, 14...Vacuum pump, 19...
- Branch valve (second switching valve), 21... Branch valve (first switching valve).

Claims (1)

[Claims] 1. A hydrogen separation device using a palladium alloy membrane is connected to a container filled with a gas to be treated containing a small amount of radioactive noble gas using hydrogen as a carrier gas through an outlet pipe, and a second A vacuum pump is connected through a first switching valve, and a storage tank is connected to the outlet of the separation device through a minute flow rate fluid pressure control device, and the outlet pipe and the storage tank are connected through a second switching valve. Radioactive waste gas treatment equipment characterized by contact.