JP2635772B2 - Gas treatment equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a gas processing apparatus using an ion implantation method in which, for example, a radioactive gas is ionized and the gas ions are injected into a metal structure. It is.

(Prior Art) In a nuclear fuel reprocessing plant that recovers uranium and plutonium from spent nuclear fuel, radioactive gas is generated during a fuel shearing process, a melting process, and the like. Among them, the most problematic radioactive gas is krypton 85 (hereinafter Kr-85).
Since Kr-85 has a very long half-life of 10.7 years, it must be stored safely for a long period of time.

As a method for safely storing a radioactive gas such as Kr-85, for example, a high-pressure cylinder storage method, a zeolite adsorption method, an ion implantation method, and the like have been developed so far.

The high-pressure cylinder storage method is a method in which a radioactive gas is sealed in a storage container such as a cylinder for permanent storage, and it is required by law to periodically perform a pressure test of the storage container. For this reason, it is necessary to transfer the stored gas every time the pressure test is performed, and there is a problem that a complicated operation is required for the gas transfer.

In addition, the zeolite adsorption method of adsorbing radioactive gas on zeolite requires treating the radioactive gas under high temperature and high pressure, and therefore has many problems to be improved before practical use.

On the other hand, the ion implantation method is not only capable of treating a radioactive gas at normal temperature and under a low pressure, but also attracts attention as a method superior to other methods in terms of economy and stability.
Hereinafter, a gas processing apparatus for processing a radioactive gas using this ion implantation method will be described with reference to FIGS. 4 to 6.

FIG. 4 shows a basic configuration of the gas processing apparatus.
This gas processing apparatus has a sealed container 1 for processing a radioactive gas which is a gas to be processed. The sealed container 1 is formed of a cylindrical ion implantation electrode 2 and an anode lid 4 and an anode bottom 5 connected to upper and lower ends of the ion implantation electrode 2 via insulating rings 3a and 3b. Is connected to an intake pipe and an exhaust pipe 7.

A gas supply tank (not shown) is connected to the intake pipe 6, and radioactive gas is introduced from the supply tank into the closed container 1 through the intake pipe 6. An exhaust pump (not shown) is connected to the exhaust pipe 7, and the inside of the sealed container 1 is exhausted by the suction force of the exhaust pump.

On the other hand, a cylindrical sputter electrode 8 is arranged in the closed vessel 1 so as to face the ion implantation electrode 2. The sputter electrode 8 is supported on the anode lid 4 via a hermetic seal 9 made of an insulating material, and a negative high voltage is applied from a sputter power supply 10. The ion implantation electrode 2 is connected to an ion implantation power supply 11,
A negative voltage is applied from the ion implantation power supply 11.

In the gas processing apparatus configured as described above, when the gas pressure in the closed vessel 1 and the voltage applied to the ion implantation electrode 2 and the sputter electrode 8 satisfy appropriate conditions (for example, when the gas pressure is 10 ⁻¹ to 10 ^{−). When} a voltage of -1 kV or less is continuously applied to the ion implantation electrode 2 and a high voltage of -1 kV or more is continuously applied to the sputter electrode 8 while maintaining the pressure at ³ Torr, a glow discharge occurs in the closed vessel 1. The radioactive gas is ionized by the glow discharge. Then, the ionized radioactive gas becomes gas ions 12 as shown in FIG. 5, and the electric field is accelerated toward the sputtering electrode 8.

The gas ions 12 thus accelerated by the electric field collide with the surface of the sputter electrode 8 and cause sputtering with the sputter electrode 8. At this time, a sputter metal 13 is generated from the sputter electrode 8 by sputtering with the gas ions 12. This sputtered metal 13 adheres to the inner surface of the ion implantation electrode 2 as shown in FIG.
At the same time, a part of the gas ions 12 are accelerated by the electric field toward the ion implantation electrode 2 as shown in FIG. 6, and are implanted into the metal accumulation layer 14 formed on the inner surface of the ion implantation electrode 2. Therefore, by repeating such a processing operation, the radioactive gas ionized in the closed vessel 1 finally becomes the metal accumulation layer 14 formed on the inner surface of the ion implantation electrode 2.
And immobilized.

(Problems to be Solved by the Invention) Incidentally, in order to stably and continuously perform such a process of injecting and fixing a radioactive gas, it is necessary to maintain a discharge state in the sealed container 1 in a glow discharge state. Here, the gas discharge is determined by the type of gas, gas pressure (P), distance between electrodes (d), and voltage (Vs) applied to the electrodes. Therefore, in order to maintain the discharge state in the glow discharge state in the discharge device in which the distance between the electrodes is constant, as described above, the gas pressure (P) in the closed vessel 1 and the ion implantation electrode 2
In addition, the power supply voltage (Vs) applied to the sputter electrode 8 must be maintained at a preset condition.

However, for example, as shown in FIG. 7, (a) when an impurity gas or vapor is ejected from the sputter electrode 8,
(B) When there are projections on the surfaces of the sputter electrode 8 and the ion implantation electrode 2, (c) When the gas pressure in the closed vessel 1 fluctuates due to the influence of disturbance on the gas pressure control system, the discharge state is glow discharge To arc discharge.

If an arc discharge occurs during the gas treatment operation, a large short-circuit current flows through the ion implantation electrode 2 and the sputter electrode 8 as shown in FIG. 8, so that the gas implantation fixation processing cannot be performed. For this reason, the pressure (P) of the gas to be treated increases, and the Pd value increases as shown in FIG. If this state continues, it may lead to melting damage of the electrodes and overload damage of the power supply, which is not preferable in terms of safety.

In addition, in order to prepare for such a situation, the operator must constantly monitor the discharge state, and the burden of labor is large.

The present invention has been made in view of such problems,
It is possible to quickly and accurately detect the occurrence of arc discharge during the gas processing operation and automatically return the discharge state to the glow discharge state, making it possible to stably and continuously perform the gas injection fixing process. It is an object of the present invention to provide a gas processing apparatus that can perform the above-described processing.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention disposes an ion implantation electrode and a sputter electrode in a closed vessel into which a gas to be treated is introduced, facing each other. A power supply voltage is applied to both electrodes to generate a glow discharge, and gas ions generated by the glow discharge are accelerated by an electric field to collide with the surface of the sputter electrode. A gas treatment apparatus for forming a metal accumulation layer on the surface and injecting and immobilizing the gas ions into the metal accumulation layer formed on the surface of the ion implantation electrode, wherein the gas pressure in the closed vessel and / or the two electrodes When the discharge state is detected from the flowing discharge current and the arc discharge occurs, the introduction of the gas to be treated is stopped and the power supply voltage applied to the two electrodes is reduced. When the gas pressure in the closed vessel decreases to a predetermined pressure after shutting off the power supply voltage, a control means for applying a power supply voltage again to the two electrodes to return to glow discharge and start introducing the gas to be treated is provided. It is provided.

(Operation) In the present invention, even if an arc discharge occurs during the gas processing operation by the glow discharge, the arc discharge can be automatically canceled and restored to the normal glow discharge. There is no need to monitor, and the burden on the operator can be reduced, and damage to the device due to arc discharge can be prevented. Further, when the gas pressure of the gas to be processed drops to a predetermined pressure after the power supply voltage is cut off, the power supply voltage is applied to the ion implantation electrode and the sputtering electrode and the introduction of the gas to be processed is started. The discharge state can be automatically returned to the glow discharge without performing, and the injection and fixation of the gas can be continuously and stably performed.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. The same parts as those shown in FIG. 4 are denoted by the same reference numerals, and description of those parts will be omitted.

FIG. 1 shows a system configuration of a gas processing apparatus according to the present invention. An automatic introduction valve is provided in an intake pipe 6 for introducing a gas to be treated (radioactive gas) stored in a gas supply tank 15 into a closed container 1. Automatic exhaust valves 17 are provided in the exhaust pipe 7 for exhausting the inside of the sealed container 1 by the suction force of the exhaust pump 18 and the suction force of the exhaust pump 18, respectively. The automatic introduction valve 16 and the automatic exhaust valve 17 are opened and closed according to a command from the controller 24. When an arc discharge occurs, the automatic introduction valve 16 is closed and the automatic exhaust valve 17 is opened, and further exhaust is performed. The pump 18 is started. Signals are input to the controller 24 from the pressure detector 19 and the discharge current monitoring circuits 20 and 21.
The discharge state is detected based on signals from 0 and 21.

The pressure detector 19 detects the gas pressure in the closed vessel 1 and is provided downstream of the automatic introduction valve 16. The discharge current monitoring circuits 20 and 21 are provided between the ion implantation electrode 2 and the ion implantation power supply 11 and between the sputter electrode 8 and the sputtering power supply.
The power supply cutoff circuits 22 and 23 are provided between the discharge current monitoring circuits 20 and 21 and the ion implantation power supply 11 and the sputtering power supply 10 for detecting the value of the discharge current flowing between the power supply circuits 10 and 10. These power cutoff circuits 22 and 23 are connected to the controller 24
When an arc discharge occurs, the power supply voltage applied to the ion implantation electrode 2 and the sputtering electrode 8 from the ion implantation power supply 11 and the sputtering power supply 10 is cut off.

A gas supply tank is provided on the exhaust side of the exhaust pump 18.
An exhaust gas retention tank 27 is provided, which is connected to the exhaust valve 15 via a return valve 25 and a gas return pipe 26. Further, the discharge current monitoring circuits 20 and 21 and the ion implantation electrode 2 and the sputtering electrode 8
Are provided with protection resistors 28, respectively.

The operation when an arc discharge occurs in such a configuration will be described with reference to FIG. 2 and FIG.

FIG. 2 shows an operation flow when an arc discharge is generated. In a normal gas processing operation (step 31), for example, the gas pressure in the sealed container 1 is adjusted to about 0.1 Torr, and Apply a voltage of 150 V or more to the sputter electrode 8-
A glow discharge is generated by applying a voltage of 1.5 kV or more, and the gas is injected and fixed while maintaining this state.
At this time, the automatic exhaust valve 17 is in the closed state, the opening of the automatic introduction valve 16 is adjusted by the controller 24, and the gas is introduced into the closed container 1.

If an arc discharge occurs during the gas processing operation by such a glow discharge (step 32), the gas injection processing is not performed. As a result, the gas pressure in the sealed container 1 increases and the discharge current sharply increases (step 33). At this time, the increase in the gas pressure is detected by the pressure detector 19, and the rapid increase in the discharge current is detected by the discharge current monitor circuits 20 and 21. Each is detected. When the gas pressure in the sealed container 1 rises due to the arc discharge and the discharge current sharply increases, the controller 24 causes the arc discharge to occur, for example, when a current close to a short-circuit current determined by the power supply voltage and the protection resistor 28 continues for a certain time. Is determined (step 34).

When the arc discharge is detected by the controller 24 in this way, first, the automatic introduction valve 16 is closed, and the introduction of gas is stopped (step 35). At the same time, the power supply cutoff circuits 22 and 23 are turned off, and the ion implantation power supply 11 and the sputtering power supply 10
The power supply voltage applied to is shut off (step 36). At the same time, the automatic exhaust valve 17 is opened, and the exhaust pump 18 is started (step 37). As a result, the gas pressure in the sealed container 1 is reduced from a state in which arc discharge is easily performed to a state in which glow discharge is easily performed. The gas in the sealed container 1 is stored in the exhaust gas retention tank 27 through the exhaust pipe 7.

On the other hand, when the gas pressure in the sealed container 1 decreases to a predetermined glow discharge pressure, the controller 24 detects this by a pressure detector.
It is detected by the signal from 19 (step 38). here,
When the gas pressure in the sealed container 1 has decreased to a predetermined pressure at which glow discharge is generated, first, the power supply shutoff circuits 22 and 23 are turned on by a command from the controller 24, and a predetermined voltage is applied to the ion implantation electrode 2 and the sputter electrode 8. The power supply voltage is applied again (step 39). At the same time, the automatic exhaust valve 17 is closed by a command from the controller 24,
Further, the exhaust pump 18 stops (step 40).

On the other hand, if the gas pressure in the closed vessel 1 is higher than the predetermined pressure, the process returns to step 37, and the exhaust pump 18 continues to exhaust the gas in the closed vessel 1. Further, when the exhaust pump 18 is stopped in step 40, the controller 24 measures the current value of the discharge current flowing between the ion implantation electrode 2 and the sputtering electrode 8 and the ion implantation power supply 11 and the sputtering power supply 10 from the discharge current monitoring circuits 20 and 21. It is detected by a signal, and it is confirmed whether or not the discharge state is glow discharge (step 41). Here, if glow discharge is confirmed, the automatic introduction valve 16 is opened, and gas introduction is started (step
42), the gas processing operation by glow discharge is restarted (step 43).

If it is determined in step 41 that the discharge is not a glow discharge, the power supply voltage applied to the ion implantation electrode 2 and the sputter electrode 8 is cut off (step 44), and the device is inspected (step 45).

FIG. 3 shows changes in the discharge current and gas pressure when a glow discharge occurs. As shown in FIG. 3, when the discharge current suddenly increases due to the occurrence of arc discharge, the ion implantation electrode 2 and the sputter electrode The voltage applied to 8 becomes zero. At the same time, the automatic introduction valve 16 is closed, the automatic exhaust valve 17 is opened, and the exhaust pump 18 is started. As a result, the pressure in the closed vessel 1 gradually decreases, and when the pressure in the closed vessel 1 decreases to a predetermined glow discharge pressure, the automatic exhaust valve 17 closes, the automatic introduction valve 16 opens, and the exhaust pump 18 stops. I do. At the same time, a power supply voltage is again applied to the ion implantation electrode 2 and the sputtering electrode 8 from the ion implantation power supply 11 and the sputtering power supply 10, and the gas processing operation by glow discharge is restarted.

As described above, in the present embodiment, when an arc discharge occurs during the gas processing operation, the power supply voltage applied to the ion implantation electrode 2 and the sputter electrode 8 is cut off and the gas introduction is stopped. It is not necessary to constantly monitor the discharge state, so that the burden on the operator can be reduced and the melting and damage of the electrodes and the overload of the power supply due to the arc discharge can be prevented. Further, when the gas pressure drops to a predetermined pressure after the power supply voltage is cut off, the power supply voltage is applied again to the ion implantation electrode 2 and the sputtering electrode 8 and the gas to be treated is introduced again into the sealed container 1, so that the discharge is performed. The state can be automatically returned to the glow discharge, and the injection and fixing of the radioactive gas can be continuously and stably performed.

In the above embodiment, the ground is taken from the anode lid 4. However, if the potential difference between the three electrodes (the ion implantation electrode 2, the anode lid 4, and the sputter electrode 8) is the above-mentioned potential difference, the earth is taken from any place. You may take it. Further, in the above embodiment, it is determined whether or not arc discharge has occurred by detecting both a sudden increase in discharge current and a rise in gas pressure. However, only one of them is detected to determine the occurrence of arc discharge. You may make it.

[Effect of the Invention] As described above, according to the present invention, an ion implantation electrode and a sputter electrode are arranged opposite to each other in a closed vessel into which a gas to be treated is introduced, and a glow discharge is performed by applying a power supply voltage to both electrodes. The gas ions generated by the glow discharge are accelerated by an electric field to collide with the surface of the sputter electrode, and a sputtered metal formed at that time forms a metal accumulation layer on the surface of the ion implanted electrode and the gas ion Is injected and fixed in a metal accumulation layer formed on the surface of the ion-implanted electrode, the discharge state is detected from the gas pressure in the closed vessel and / or the discharge current flowing through the two electrodes, and the arc is detected. When a discharge occurs, the introduction of the gas to be treated is stopped, and the power supply voltage applied to both electrodes is cut off. When the gas pressure in the vessel falls to a predetermined pressure, a control means is provided for applying a power supply voltage again to the two electrodes to return to glow discharge and to start introducing the gas to be treated.

Therefore, an arc discharge is generated during the gas processing operation, and this can be detected quickly and accurately, and the discharge state can be automatically returned to the glow discharge, so that the gas injection fixing process is continuously performed stably. Can be provided.

[Brief description of the drawings]

1 to 3 show one embodiment of the present invention, FIG. 1 is a system configuration diagram of a gas processing apparatus, FIG. 2 is an operation flow diagram when a glow discharge occurs, and FIG. FIG. 4 to FIG. 9 are explanatory diagrams of the prior art. DESCRIPTION OF SYMBOLS 1 ... Closed container, 2 ... Ion implantation electrode, 3a, 3b ... Insulation ring, 4 ... Anode cover, 6 ... Gas introduction pipe, 7 ... Exhaust pipe, 8 ... Sputter electrode, 10 ... Sputter Power supply, 11 ...
... Ion implantation power supply, 12 ... Gas ion, 13 ... Sputtered metal, 14 ... Metal accumulation layer, 15 ... Gas supply tank, 16 ...
… Automatic introduction valve, 17 …… Auto exhaust valve, 18 …… Exhaust pump,
19 …… Pressure detector, 20,21 …… Discharge current monitor circuit, 22,
23: Power cutoff circuit, 24: Controller.

Claims (1)

(57) [Claims] An ion implantation electrode and a sputter electrode are arranged in a closed vessel into which a gas to be treated is introduced, and a power supply voltage is applied to both electrodes to generate a glow discharge. The gas ions thus formed are subjected to an electric field acceleration to collide with the surface of the sputter electrode, and a sputtered metal formed at that time forms a metal accumulation layer on the surface of the ion implanted electrode and forms the gas ions on the surface of the ion implanted electrode. In the gas treatment apparatus for injecting and fixing the accumulated metal layer, when the discharge state is detected from the gas pressure in the closed vessel and / or the discharge current flowing through the two electrodes, the arc processing is performed when an arc discharge occurs. The introduction of gas is stopped and the power supply voltage applied to the two electrodes is cut off. After the power supply voltage is cut off, the gas pressure in the closed container is reduced to a predetermined pressure. Gas treatment apparatus being characterized in that comprises a control means for starting the introduction of the gas to be treated with the case by applying again a power supply voltage between the electrodes revert to the glow discharge.