JPH0429438Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a radioactive gas immobilization treatment method in which radioactive gas in a fission product gas is ionized and injected into a metal medium.

[Technical background of the idea and its problems] If a harmful amount of radioactivity is released into the environment at a nuclear facility, the effects may be wide-ranging and long-lasting, so ensuring safety is extremely important. becomes.

Nuclear fuel reprocessing plants recover uranium and plutonium from spent fuel, but this also generates radioactive waste, which must be disposed of appropriately. Among the radioactive wastes, gaseous waste includes krypton-85 (Kr-85), which has a long half-life of 10.5 years, so collecting it and safely storing or disposing of it is an important issue. It's summery.

Conventional methods for storing radioactive waste gas include sealing it in a pressure vessel such as a cylinder for permanent storage, but the method of sealing it in a pressure vessel has problems in terms of safe storage over a long period of time. For example, pressure vessels are required to undergo periodic pressure tests, which have the drawback of requiring complicated and dangerous work such as transferring stored gas each time.

Among gaseous wastes, methods for treating Kr-85 include, in addition to the above-mentioned method of storing it in pressure vessels such as cylinders, adsorption on zeolite, ionization injection fixation, etc.; However, there are many problems that need to be improved before the zeolite adsorption method can be put into practical use.

On the other hand, the ion implantation method can be disposed of at room temperature and low pressure, and is considered to be superior to other methods in terms of long-term storage safety, and is being researched and developed around the world. FIG. 3 is a vertical cross-sectional view showing an outline of a conventionally proposed implantation device for ionizing and implanting radioactive gas, and FIGS. 4 and 5 are diagrams for explaining the operating principle of the device shown in FIG. 3. It is an explanatory diagram. Hereinafter, a conventional method for ionization implantation and fixation of Kr-85 will be explained with reference to FIGS. 3, 4, and 5.

In an ionization chamber 2 provided in a cylindrical container 1, a cylindrical electrode 5 to which a cooling pipe 3 and a lead wire 4 are attached is arranged at the center thereof. The cooling pipe 3 and the lead wire 4 are insulated from the upper lid 7 by an insulator 6 such as a hermetic seal. Further, an introduction pipe 9 for introducing Kr-85 gas and an exhaust pipe 11 for exhausting the inside of the container 1 are installed on the upper lid 7 of the container 1, and the Kr-85 gas is passed through valves 8 and 10, respectively. 85 gas is introduced and the air inside the container is exhausted. Further, a cooling pipe 12 is wound around the outer peripheral surface of the container 1 . Note that reference numeral 14 is a cumulative layer consisting of a sputtered ion layer of an electrode material produced by sputtering an ion-implanted Kr-85 ion layer and the electrode 5. In FIGS. 4 and 5, reference numeral 15 indicates Kr-85 ions, and reference numeral 16 indicates sputtering ions ejected from the electrode 5.

Next, a method of ionizing, implanting and fixing Kr-85 gas using the above-mentioned apparatus will be explained.

Exhaust pipe 1 using an exhaust device (not shown) such as an ion pump, an axial molecular pump, or an oil diffusion pump.
After the air in the container 1 is exhausted from the container 1 to a desired degree of vacuum, for example, about 5×10 ^-7 Torr, the valve 10 is closed, and then the valve 8 is opened to release Kr from a cylinder or the like into the container 1. -85 gas is supplied. container 1
When Kr-85 gas at a constant pressure, for example, about 0.1 Torr, is sealed inside, the valve 8 is closed. Further, a cooling medium such as water is caused to flow through the cooling pipes 3 and 12 to cool the nickel electrode 5 and the container 1, for example. A DC high voltage power source (not shown) is connected between the container 1 and the lead wire 4 connected to the nickel electrode 5, and a high voltage of, for example, about 2 to 5 KV is applied to the nickel electrode 5 with alternating polarity. so that When a high positive voltage is applied to the nickel electrode 5, the ionized Kr-85 ions are injected and planted into the inner surface of the container 1 as shown in FIG. When voltage is applied, Kr-85 ions15 as shown in Figure 5
bombarded the surface of the nickel electrode 5 to sputter the nickel electrode 5 material, and the sputtered ions were planted on the inner surface of the container 1.
Coated on top of Kr-85 ions 15.
In this way, a positive voltage of 2 to 5 KV is applied to the nickel electrode 5,
Apply a negative voltage at regular intervals, for example 5 when coating.
Kr-85 is applied to the inner surface of the cylindrical container 1 for 1 second during Kr-85 ion implantation.
The 85 ion layer and the sputtered ion layer of the electrode 5 material are accumulated to form a cumulative layer.

The ion implantation method for Kr-85 that has been proposed so far is as described above, but as mentioned above, this ion implantation and immobilization processing device cannot produce Kr-85 unless a high voltage of positive and negative voltages is applied alternately to the cylindrical electrode. −85
A cumulative layer of ions and electrode material ions cannot be formed. Therefore, in this device, the polarity of the DC high voltage power source must be changed at regular intervals. For this reason, a relay is installed after the DC high voltage power supply.
It becomes necessary to connect a polarity converter incorporating a polarity converter etc. However, since this polarity converter has a mechanical drive part, there is a problem in that the service life is inevitably shortened due to wear.

[Purpose of the invention] The invention was made in view of the above-mentioned circumstances, and its purpose is to ionize, implant, and fix radioactive waste gas generated during nuclear fuel reprocessing, such as Kr-85 gas, into an electrode. It is an object of the present invention to provide an ionization implantation fixation processing device that can form a cumulative layer of radioactive gas ions and sputtered ions of an electrode material without changing the polarity of a high-voltage power source to be applied.

[Summary of the invention] The invention comprises a cylindrical container into which a radioactive gas is introduced, disc-shaped cathode electrodes arranged at the upper and lower parts of an ion source chamber formed in the center of the container, and the cathode. a cylindrical anode electrode arranged outside the electrode and having a plurality of through holes; a cylindrical acceleration electrode arranged outside the anode electrode and having a plurality of through holes; a cylindrical sputter electrode having a through hole;
a first DC high voltage power supply that applies a high voltage such that the anode electrode is a positive electrode and the cathode electrode is a negative electrode; the anode electrode is a positive electrode, the acceleration electrode is a negative electrode, and between the anode electrode and the cathode electrode; A second DC high voltage power supply that applies a higher voltage than the applied high voltage is provided, and a cumulative layer of radioactive gas ion layer is formed on the inner wall surface of the cylindrical container while continuously applying a DC high voltage of the same polarity. The present invention relates to a radioactive gas immobilization processing apparatus characterized in that the radioactive gas is formed.

[Embodiment of the invention] An embodiment of the invention will be described with reference to the drawings.

1 and 2 are a longitudinal sectional view and a transverse sectional view showing an embodiment of the immobilization processing apparatus of the present invention. To explain its structure, a cylindrical accelerating electrode 23 is provided with a plurality of through holes in a cylindrical container 22 provided with a cooling medium inlet 20 and an outlet 21.
is installed, and a cylindrical sputter electrode (for example, nickel) 24 with a plurality of through holes provided on the outside of the electrode 23 is arranged concentrically with the electrode 23. The through hole of the sputter electrode 24 has a tapered shape with a smaller diameter on the outside of the cylinder than on the inside. Further, a lid 31 is provided on the upper and lower surfaces of the cylindrical container 22 with an insulator 25 made of, for example, ceramics interposed therebetween, and connected to the lid 31 is a cylindrical anode electrode 26 provided with a plurality of through holes. It is arranged concentrically with the accelerating electrode 23 and the sputter electrode 24. Each of these electrodes 23, 2
The through holes 4 and 26 are arranged at the same position in the radial direction as shown in the drawing. A lid 2 with an insulator 27, such as a hermetic seal, embedded in the center above and below the anode electrode 26.
8 is arranged, and the hermetic seal 2
A lead wire 30 to which a disk-shaped cathode electrode 29 is attached is arranged at the center of the electrode 7 . Further, an exhaust pipe 32 is attached to the lid 31 below the anode electrode 26, and the inside of the cylindrical container 22 is exhausted through a vacuum valve 33. On the other hand, a gas introduction pipe 34 is attached to the upper lid 31 for introducing Kr-85 gas into the container 22 by opening and closing a valve 35. The space surrounded by the anode electrode 26 and the lid 28 is an ion source chamber 36
It is. A first DC high-voltage power supply 37 is connected between the lead wire 30 of the cathode electrode 29 and the lid 31 of the anode electrode 26, with the cathode side as a negative pole and the anode side as a positive pole. Further, the positive electrode of a second DC high voltage power source 38 is connected to the positive electrode side of the power source 37, and the negative electrode of the power source 38 is grounded and connected to the cylindrical container 22.

Next, a method of ionizing, implanting and fixing Kr-85 gas using the above-mentioned apparatus will be explained.

The valve 33 is opened, and the inside of the cylindrical container 22 is pumped through the exhaust pipe 32 using an exhaust device (not shown), for example, 5 times.
Exhaust to about ×10 ^-7 Torr. The inside of the container 22 is 5×
When the pressure drops to 10 ^-7 Torr, close the valve 33, then open the valve 35 and introduce Kr-85 gas into the container 22 from the gas inlet 34, until the pressure inside the container 22 reaches 10 ^-2 ~ When the pressure reaches about 10 ^-3 Torr, close the valve 35 and confirm that the pressure inside the container 22 does not change, that is, there is no leakage. Thereafter, a DC high voltage of 1 to 3 KV is applied between the cathode electrode 29 and the anode electrode 26 by the first DC high voltage power supply 37 to cause Kr-85 gas discharge in the ion source chamber 36. Thereafter, when a DC high voltage of 5 to 10 KV is applied between the anode electrode 26 and the accelerating electrode 23 by the second DC high voltage power supply 38, ionized Kr- ions are released from the Kr- gas discharge in the ion source chamber 36. is extracted and accelerated, and ionized and implanted into the inner wall of the cylindrical container 22. At the same time, some of the Kr-85 ions impact the sputter electrode 24 to release sputter ions and deposit the sputter ions on the inner wall of the container 22. As a result, an accumulated layer of Kr-85 ions and sputtering ions is formed on the inner wall surface of the container 22. Note that while the above operations are being performed, the container 22 becomes quite high in temperature, so it is necessary to continue flowing a cooling medium such as water. In addition, if the pressure inside the container 22 drops to about 10 ^-3 Torr or less as a result of processing the Kr-85 gas in the above operation, open the valve 35 and remove the pressure inside the container 22.
Increase the internal pressure to about 10 ^-2 to ^{10 -3} Torr.

In the above example, nickel was used as the sputtering electrode material, but other metals that easily cause sputtering may also be used, such as an alloy of nickel and lanthanum, lanthanum, copper, copper alloy, gold, silver, and aluminum alloy. be able to. Moreover, it is of course possible to use a cooling medium other than water.

Moreover, although the above embodiment relates to the immobilization treatment of Kr-85, it can be similarly applied not only to Kr-85 but also to other radioactive gases.

[Effects of the invention] As explained above, according to the radioactive gas immobilization processing apparatus of the present invention, there is no need to change the polarity of the DC high-voltage power supply at fixed time intervals, unlike conventionally proposed apparatuses. Ionization implantation and immobilization treatment of Kr-85 gas can be performed while continuously applying a DC high voltage of the same polarity. Therefore, since there is no need to use a polarity converter with a short life, the overall life can be extended.

[Brief explanation of the drawing]

Figures 1 and 2 are longitudinal and cross-sectional views showing an embodiment of the radioactive gas immobilization processing device of the present invention, and Figure 3 is a conventionally proposed injection device for ionizing and injecting radioactive gas. 4 and 5 are explanatory diagrams for explaining the operating principle of the apparatus shown in FIG. 3. 20...Cooling water inlet, 21...Cooling water outlet, 2
2... Cylindrical container, 23... Accelerating electrode, 24...
Sputter electrode, 25... Insulation, 26... Anode electrode, 27... Hermetic seal, 28...
Lid, 29... cathode electrode, 30... lead wire,
31...Lid, 32...Exhaust pipe, 34...Gas introduction pipe, 36...Ion source chamber, 37...First DC high voltage power supply, 38...Second DC high voltage power supply.

Claims (1)

[Claims for Utility Model Registration] (1) A cylindrical container into which a radioactive gas is introduced, and disc-shaped cathode electrodes arranged at the upper and lower parts of an ion source chamber formed in the center of the container,
a cylindrical anode electrode arranged outside the cathode electrode and having a plurality of through holes; a cylindrical acceleration electrode arranged outside the anode electrode and having a plurality of through holes; a cylindrical sputter electrode having a plurality of through holes, and a first electrode to which a high voltage is applied such that the anode electrode becomes a positive electrode and the cathode electrode becomes a negative electrode.
a DC high voltage power supply, the anode electrode is a positive electrode,
A radioactive gas immobilization process characterized in that the accelerating electrode is a negative electrode and is comprised of a second DC high voltage power supply that applies a higher voltage than the high voltage applied between the anode electrode and the cathode electrode. Device. (2) The radioactive gas immobilization processing apparatus according to claim 1, wherein the anode electrode, the cathode electrode, and the sputter electrode are arranged in concentric circles. (3) The through holes of the anode, accelerating electrode, and sputter electrode are arranged at the same position in the radial direction, and the through hole of the sputter electrode is narrowly tapered outward. Claim 1 The radioactive gas immobilization processing device described in 2.