JPH01162197A - Storage of radioactive gas - Google Patents

Abstract

PURPOSE:To maintain a stable electric discharge for a whole device, by providing a primary discharging part producing an electric discharging plasma for ion injections which have different distances of electrodes between a vessel and electrodes, and a secondary discharging part for a stable electric discharge. CONSTITUTION:A storage device of a radioactive gas is composed of a vessel 11 which is a sealed outer electrode into which a processed gas is introduced, and an electrode 12 which is a target material placed in the vessel 11 and also a direct current high voltage power supply 6 supplying a high voltage to the electrode 12. The primary discharging part 13 is placed at a position having an appropriate inter-electrodes distance for metal atoms from the electrode 12 to move to inside the vessel 11 and to stick and laminate themselves on an inside surface of the vessel. The secondary discharging part 14 is placed at a position having an appropriate inter-electrodes distance for discharging conditions to be maintained even if a pressure changes. When discharging is maintained in the device and a condition returns to a previous one by an increased gas pressure, discharging spreads to the part 13, therewith discharging is not intercepted. Through this procedure, a stable electric discharging is maintained throughout the device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a radioactive gas storage device for ionizing a radioactive gas in a fission product gas and injecting the ionized gas into a metal substrate for storage.

(Prior art) Generally, in nuclear facilities such as nuclear fuel reprocessing plants,
If a harmful amount of radioactivity is released into the environment, the effects could be wide-ranging and long-lasting, so safety measures are required to be much stricter than in other general industries. There is.

In the nuclear fuel reprocessing plant mentioned above, uranium and platonium are recovered from spent nuclear fuel, but at the same time, among the accompanying radioactive waste including fission products, gaseous waste that may pose a problem is krypton-85 ( Below K r
K r-85 has a long half-life of 10.7 years, so it needs to be stored for a long time.

For this reason, a device is needed to reliably store radioactive gases such as Kr-85, and devices for immobilization using high-pressure cylinder storage methods, zeolite adsorption methods, and ion implantation methods have been developed or are currently under development. It is.

FIG. 2 shows a conventional radioactive gas storage device using the ion implantation method, and the conventional device will be explained with reference to FIG. That is, this radioactive gas storage device includes a sealed external electrode container 1 (hereinafter referred to as container 1) into which a gas to be treated is introduced, a cylindrical inner target electrode 2 disposed inside this container 1, and A high voltage is applied to a lid 3 that closes the upper end opening of the container 1, an inlet pipe 4 for the gas to be treated attached to the base 3, a suction pipe 5 for reducing the pressure inside the container 1, and the electrode 2. It consists of a DC high voltage power supply 6 for The inside of the container 1 is maintained at a constant low pressure by a vacuum pump (not shown) connected to the suction pipe 5.

A voltage is applied between the container 1 and the electrode 2 by an external power source 6.

In such a radioactive gas storage device, the pressure inside the container 1 and the electric current between the container 1 and the t! It is well known that a discharge occurs throughout the container 1 when the voltage applied between it and i12 satisfies appropriate conditions. This discharge causes K r-85
is ionized and becomes an ionic state, and a discharge plasma is formed.

When a negative voltage of IKV or higher is applied to the container 1 and a negative voltage of V or higher to the electrode 2 by the power source 6, the K r-as ions 7 ionized by the discharge move along the electric field. It is accelerated and collides with the surface of the electrode 2, causing the electrode 2 to sputter. The sputtered metal atoms adhere to and stack on the inner surface of the opposing container 1 to form a coating layer 8 .

At the same time, some K r-85 ions 7 are directly accelerated toward the electric field of the container 1 and are implanted into the coating layer 8 described above.

In the storage device configured in this manner, it was necessary to operate stably for a long period of time, and in particular, it was necessary to sustain the discharge plasma generated between the electrodes 1 and 2.

(Problems to be Solved by the Invention) However, in the above device, the sputtered metal atoms reach the inner surface of the opposing container 1 and are deposited in a layer, so it must be operated with the pressure of the radioactive gas kept low, and external disturbances If the pressure drops even slightly due to reasons such as this, the conditions for sustaining the discharge no longer hold and the discharge stops, causing a phenomenon in which the operation stops.

The present invention was developed to solve the above problems, and provides a radioactive gas storage device that can operate continuously without stopping discharge even if the pressure changes due to disturbances or the like.

[Structure of the Invention] (Means for Solving the Problems) The present invention comprises a sealed container that serves as an outer electrode into which a processing gas is introduced, an electrode that serves as a target material disposed inside the container, and an electrode that serves as a target material arranged inside the container. In a radioactive gas storage device equipped with a DC high voltage power supply that applies a high voltage to an electrode, a first discharge part that creates a discharge plasma for ion implantation with a different electrode spacing between the container and the electrode and a stable A second discharge portion that generates discharge is provided so that stable discharge can be maintained as a whole of the device.

(Function) The first discharge part for ion implantation has an electrode spacing suitable for ion acceleration sputtering, and the second discharge part is for stable discharge. Even if the gas pressure decreases, the second discharge portion satisfies the discharge conditions. Therefore, the discharge continues in the device, and when the gas pressure rises and returns to the previous state, the first discharge portion (lower discharge) spreads and stable operation is possible without stopping the discharge.

(Example) Hereinafter, an example of a radioactive gas storage device according to the present invention will be described with reference to FIG.

In FIG. 1, the same parts as in FIG. 2 are given the same reference numerals.

Reference numeral 11 denotes an outer electrode container with a long lower part, which serves as a substrate. Inside this container 11, an inner electrode 12, which serves as a target material, is arranged. A lid 3 is provided at the top opening of the container 11. There is.

An inlet pipe 4 for the gas to be processed and a suction pipe 5 for reducing the pressure inside the container 11 are attached to the fi3. Also, container 11
A DC high voltage power source 6 is provided between the electrode 12 and the electrode 12 via leads l16a and 6b.

Here, the space between the container 11 and the electrode 12 has a structure in which a first discharge part 13 and a second discharge part 14 exist, and the first discharge part 13 and the second discharge part 14 exist.
The discharge portion 13 has a short inter-electrode distance, and the second discharge portion 1
4 is set so that the distance between the lower end of the inner electrode 12 and the bottom surface of the container 11, that is, the distance between the electrodes becomes longer.

That is, the first discharge portion 13 has a distance between the electrodes, for example, a pressure of 5 x 1, which is suitable for the metal atoms sputtered from the inner electrode 12 to move to the inner surface of the container 11 and deposit and stack them.
For O-2 TOrr, it is set to 4 to 5 Cm, and the second discharge part 14 is set to a distance between the electrodes that maintains the discharge condition even if the pressure fluctuates, for example, if the pressure is 5 x 1 G' Torr, it is set to 10 cn+ to 20 c+1. It is set.

In an apparatus with such a configuration, the gas pressure under normal operating conditions is, for example, 5 x 1 G' Torr.
Assuming that the gas drops to 2 x 10' Torr due to disturbance etc., the gas pressure (P) x cap (d) is the first
The discharge portion becomes 1.3 te 10-' Torr -cm, and no discharge occurs at a chisel pressure of 1500V. However, the second discharge portion 14 is 2 x 10 - blind ~ 4 x 10
' Since the discharge can be sustained at Torr-crl, the discharge in the entire device can be maintained. Here, the pressure is 2
When the pressure starts to rise from 1 O-2 Torr to 5×1 O-2 Torr, it gradually spreads from the second discharge portion 14 to the first discharge portion 13, returning to the operating state before the disturbance occurred.

FIG. 3 is a Paschen curve diagram showing krypton (K'') discharge characteristics for explaining the principle of the above embodiment. That is, the first discharge portion 13 for ion implantation is shown in FIG.
In addition, by providing a second discharge portion 14 for stable discharge, the pd can be increased to 5×10 as shown in FIG.
-1500 in the second discharge part ranging from 1 to 10'
The discharge can be maintained sufficiently stably with a voltage of V.

[Effects of invention According to the present invention, the following effects are achieved.

Even if the internal gas pressure drops due to some kind of disturbance, the discharge will not stop, and when the gas pressure returns to its normal value, the discharge range will gradually expand and the normal operating state can be restored.

Furthermore, even if the coating layer were to peel off and fall, it would remain at the bottom of the container, and problems such as normal discharge and conduction between electrodes would not occur.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional configuration diagram showing an embodiment of a radioactive gas storage device according to the present invention, FIG. 2 is a cross-sectional configuration diagram showing a conventional radioactive gas storage device, and FIG. 3 is a detailed explanation of the present invention. FIG. 1.11...Container 2.12...Electrode 3...Base 4...Gas pressure introduction pipe 5...Gas suction pipe 6 ...Power supply 13 ...First discharge portion 14 ...
...Second Discharge Part Applicant Toshiba Corporation Patent Attorney Satoshi Suyama - Figure 1 Figure 2 11 pages 6 inches 2a (Figure 3

Claims (1)

[Claims] A radioactive gas that is equipped with a sealed container that serves as an outer electrode into which the gas to be treated is introduced, an electrode that serves as a target material placed inside this container, and a DC high voltage power supply that applies a high voltage to this electrode. A radioactive gas storage device, characterized in that first and second discharge portions having different electrode spacings are provided between the container and the electrodes.