JPH0419600A - Treatment of radioactive gas - Google Patents

Abstract

PURPOSE:To increase the amt. of the gas treated per unit time without decreasing the amt. of the gas per unit electric energy by mixing a radioactive gas with a gaseous impurity and introducing the gaseous mixture into a hermetic vessel. CONSTITUTION:The radioactive gas is introduced into the hermetic vessel 1 and a glow discharge is generated by injecting ions into the vessel 1 and impressing a high voltage to sputtering electrodes 3, 2, by which the gas is ionized. This radioactive gas is injected to a sputtered metallic layer 14 formed on the surface of an electrode 8 and is thereby subjected to a solid soln. treatment. The radioactive gas is mixed with the gaseous impurity in a gas mixing tank 7 and the gaseous mixture is introduced into the vessel 1 at this time. The ionization rate of the gas is increased by Penning ionization and the amt. of the gas treated per unit time is improved without decreasing the amt. of the gas treated per unit electric power.

Description

DETAILED DESCRIPTION OF THE INVENTION [Objective of the Invention (Industrial Application Field) The present invention relates to a radioactive gas processing method for fixing radioactive gas generated, for example, in a nuclear fuel reprocessing plant.

(Conventional technology) At nuclear fuel reprocessing plants that recover uranium and plutonium from spent nuclear fuel, radioactive gaseous waste is generated during the fuel melting process, so safety must be strictly ensured. Among the radioactive gaseous waste generated in such nuclear fuel reprocessing plants, the gaseous waste that is likely to cause the most problems is krypton-85 (hereinafter abbreviated as Kr-85), and this Kr-85 has a half-life. Since it has a very long life of 10.7 years, it must be stored safely for a long time.

High-pressure cylinder storage methods, zeolite adsorption methods, and ion injection methods have been developed as methods for storing radioactive gases such as Kr-85, but radioactive gases are sealed in storage containers such as cylinders for permanent storage. Under the High Pressure Cylinder Storage Law, it is required by law to periodically conduct pressure tests on storage containers.

Therefore, it is necessary to transfer the stored gas every time a pressure test is performed, and there is a problem in that complicated work is required to transfer the stored gas. In addition, the zeolite adsorption method, in which radioactive gas is adsorbed onto zeolite, requires the radioactive gas to be treated at high temperature and pressure, so there are many problems that need to be improved before it can be put to practical use.

Meanwhile, a radioactive gas is introduced into the sealed container, and a high voltage is applied to an ion implantation electrode and a sputtering electrode provided oppositely in the container to generate a glow discharge. The ion implantation method, in which gas is injected and fixed into a sputtered metal layer formed on the surface of an ion implantation electrode, not only allows radioactive gases to be processed at room temperature and low pressure, but is also superior in terms of safety and economy. This method is attracting attention.

(Problem to be solved by the invention) By the way, when treating a large amount of radioactive gas generated in a nuclear fuel reprocessing plant using the ion implantation method, it is necessary to improve the amount of gas processed per unit time and to reduce the amount of gas processed per unit amount of electricity. It is also necessary to improve gas throughput. However, in order to improve the amount of gas processed per unit time, it is necessary to increase the gas pressure inside the sealed container. There was a problem with the amount decreasing. This is because sputtered metal atoms sputtered from the sputtering electrode collide with gas atoms in the sealed container and lose their kinetic energy, making it impossible to effectively form a sputtered metal layer on the surface of the ion implantation electrode. .

The present invention was made in view of these problems, and
The purpose is to provide a radioactive gas processing method that can improve the amount of gas processed per unit time without reducing the amount of gas processed per unit electric energy.

[Structure of the Invention (Means for Solving the Problems)] In order to solve the above problems, the present invention introduces a radioactive gas into a sealed container, and an ion implantation device provided oppositely in the container. A radioactive gas that is immobilized by applying a high voltage to the electrode and the sputtering electrode to generate a glow discharge, and injecting the radioactive gas ionized by the glow discharge into the sputtered metal layer formed on the surface of the ion implantation electrode. In the treatment method, the radioactive gas is mixed with an impurity gas and introduced into the container.

(Function) In the present invention, by mixing radioactive gas with impurity gas and introducing it into a closed container, the ionization rate of the radioactive gas increases due to Penning ionization, so the amount of gas processed per unit electric power is reduced. It is possible to improve the amount of gas processed per unit time without causing any problems.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 3.

Figure 1 is a schematic diagram showing an example of a radioactive gas processing apparatus using the ion implantation method.
It consists of a closed container 1 into which a radioactive gas such as R is introduced, and a cylindrical sputtering electrode 2 placed at the center of the closed container 1.

The sealed container 1 is formed of a bottomed cylindrical ion implantation electrode 3 forming a container body, and an anode lid 4 that closes the upper opening of the ion implantation electrode 3. An exhaust pipe 5 is connected to the anode lid 4. ing. This exhaust pipe 5 is connected to a suction device (not shown) such as a vacuum pump, and radioactive gas is introduced into the closed container 1 through the suction pipe 6 by the suction force of this suction device. A gas mixing tank 7 for mixing a radioactive gas such as Kr and an impurity gas such as Ne is connected to the intake pipe 6, and the radioactive gas containing the impurity gas is discharged from the gas mixing tank 7 into the closed container 1. is being supplied to.

The ion implantation electrode 3 is connected to an ion implantation power source 8, and a negative potential is applied from the ion implantation power source 8. Further, the sputter electrode 2 is connected to a sputter power source 9, and a negative potential is applied from the sputter power source 9. The ion implantation electrode 3 and the sputtering electrode 2 are electrically insulated from the anode lid 4 by an insulating material 10.11, and the anode lid 4 is at ground potential.

Next, a method of processing radioactive gas using the radioactive gas processing apparatus configured as described above will be described.

First, a suction device (not shown) connected to the exhaust pipe 5 is driven to introduce radioactive gas containing a trace amount of impurity gas (for example, Ne gas) into the closed container 1 through the intake pipe 6 . Then, the pressure inside the closed container 1 is set to, for example, 10-1 to 1O-3T.
When a negative potential of -1 kV or less is applied from the ion implantation power supply 8 to the ion implantation electrode 3 and a negative potential of -1 kV or more is applied to the sputter electrode 2 from the sputter power supply 9 while maintaining the ion implantation electrode 3 at A glow discharge occurs. The radioactive gas introduced into the sealed container 1 by this glow discharge is ionized and becomes gas ions.

At this time, since the potential applied to the sputter electrode 2 is relatively higher than the potential applied to the ion implantation electrode 3, the radioactive gas that has become gas ions 12 is transferred to the sputter electrode 2, as shown in FIG. It is accelerated along the electric field and collides with the sputter electrode 2. As a result, sputtered metal atoms 13 fly out from sputtered electrode 2 and adhere to the inner peripheral surface of opposing ion implantation electrode 3 to form sputtered metal layer 14 .

Further, a part of the radioactive gas that has become gas ions 12 is accelerated along the electric field of the ion implantation electrode 3 and injected into the sputtered metal layer 14, as shown in FIG. Therefore, by repeating such a phenomenon, the radioactive gas introduced into the closed container 1 is injected into the sputtered metal layer 14 formed on the surface of the ion implantation electrode 3 and fixed therein.

By the way, when radioactive Kr gas containing an impurity gas such as Ne is introduced into the closed container 1, metastable Ne atoms in an excited state collide with neutral Kr atoms, and the Kr atoms are ionized by Penning ionization. Therefore, by mixing a radioactive gas such as Kr with an impurity gas such as Ne and introducing it into the closed container 1, the ratio of Kr gas ions to neutral Kr atoms, that is, the ionization ratio of the radioactive gas increases, so the closed container A large amount of Kr gas ions can be generated even when the gas pressure inside the device 1 is low, and the amount of gas processed per unit time can be improved without reducing the amount of gas processed per unit electric power.

In addition, when mixing impurity gas such as Ne with radioactive gas, 1
It is preferable to mix about 2% impurity gas.

[Effects of the Invention] As explained above, in the radioactive gas processing method according to the present invention, the radioactive gas is mixed with impurity gas and introduced into the closed container, so that the amount of gas processed per unit electric power is reduced. It is possible to improve the amount of gas processed per unit time.

[Brief Description of the Drawings] Figures 1 to 3 are diagrams for explaining the radioactive gas processing method according to the present invention, and Figure 1 is a schematic diagram of a radioactive gas processing apparatus, and Figures 2 and 3 are diagrams for explaining the radioactive gas processing method according to the present invention. FIG. 4 is an explanatory diagram showing the operation of the apparatus, and FIG. 4 is a diagram showing the relationship between the amount of gas processed per unit time and the amount of gas processed per unit electric power by the ion implantation method. DESCRIPTION OF SYMBOLS 1... Airtight container, 2... Sputtering electrode, 3... Ion implantation electrode, 4... Anode lid, 5... Exhaust pipe, 6...
... Intake pipe, 7... Gas mixing tank, 8... Ion implantation power source, 9... Sputtering power source, 12... Gas ion, 13... Sputtered metal atom, 14... Sputtered metal layer .

Claims (1)

[Claims] Introducing radioactive gas into a sealed container,
A high voltage is applied to an ion implantation electrode and a sputter electrode that are provided facing each other in the container to generate a glow discharge, and the glow discharge ionizes the radioactive gas to form sputters on the surface of the ion implantation electrode. 1. A method for treating a radioactive gas which is injected into a metal layer and fixed therein, the method comprising: mixing the radioactive gas with an impurity gas and introducing the mixture into the container.