JPS60174899A - Polishing device for metallic surface - Google Patents

Abstract

PURPOSE:To polish a metallic surface and to remove thoroughly radioactive contaminants from a metallic surface contaminated by a radioactive material by conducting electricity between the metallic surface as anode and a cathode facing said surface in parallel therewith while injecting an aq. neutral inorg. salt soln. contg. hard insulating particles to the metallic surface which is the anode. CONSTITUTION:A parallel cathode plate 2 provided with an injection nozzle 3 is disposed in the upper part of a nuclear reactor member 1 onto which a radioactive material sticks and of which the surface of the material itself is irradiated. The metallic plate 1 itself is connected via a juncture 5 to the anode of a DC power source 4. An anode 1 and cathode 2 are insulated by an insulating material 6 and electricity is conducted thereto while the electrolyte in an electrolyte storage tank 1 is injected to the surface of the anodic plate 1 to be treated from the nozzle 3. The electrolyte contg. insulating particles such as glass particles or ceramics such as alumina and dissolved therein with NaNO3, NaONO2, Na2SO4, etc. at 5-30% is used. The radioactive deposit as well as the surface of the member 1 are ground by which the radioactive contaminants are removed therefrom.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a metal surface polishing device, particularly for polishing and decontaminating the surface of metal on which radioactive substances generated in nuclear power plants, etc. have adhered. This invention relates to a metal surface polishing device for use in metal surface polishing.

[Technical Background of the Invention and Problems Therewith] Generally, radioactive metal waste generated at nuclear power plants and the like is permanently stored within the nuclear power plant to prevent it from imparting fV'Ef to the environment. However, if such radioactive metal waste is stored permanently, the amount of radioactive metal waste will continue to increase, making it difficult to secure storage space. In particular, piping and the like generated during the renovation of tiered facilities at nuclear power plants and the like are large in size and cannot be easily reduced in volume, making it difficult to store them. For this reason, consideration is being given to decontaminating radioactive metal waste to reduce its radioactivity level to the level found in nature, that is, to the background level, so that it can be handled in the same way as general waste. However, since the material on the surface of radioactive metal waste is itself radioactive, complete decontamination cannot be achieved simply by removing the radioactive cladding deposited on the surface; the metal itself must also be polished to remove the radioactive cladding. It is necessary to remove the surface layer. During radioactive decontamination, it is easy to remove the crud using a honing decontamination device that uses abrasive grains such as glass or grinding using a grindstone, but on the other hand, the grinding speed of the material itself is similar, and the grinding depth is There are also limits. Furthermore, it is necessary to replace the grindstone depending on the metal material, and it is difficult to reliably polish and decontaminate these surfaces.

In addition, the conventional electrolytic polishing method is known as a method of polishing the metal itself, but depending on the material of the metal, an oxide film is formed on the surface of the metal, and radioactive substances are incorporated into this oxide film, resulting in recontamination. There's a problem. For this reason, a highly concentrated electrolyte with a strong acid is used, and the electrolytic conditions must be controlled with high precision, making it difficult to put it into practical use. Furthermore, if insulating deposits such as paint are present, decontamination is difficult because electrolytic polishing is not performed.

[Purpose of the Invention] The present invention was made based on the above circumstances, and its purpose is to reliably polish the surface of radioactive metal waste, completely decontaminate it, and reduce the radioactivity level to the background level. Provides equipment for polishing radioactive metal surfaces that can be degraded and decontaminated to the point where they can be treated like general waste.

It's about doing.

[Summary of the Invention] That is, the present invention uses a metal surface of nuclear equipment contaminated with radioactive substances as an anode, a cathode facing parallel to the metal surface, and a neutral inorganic salt aqueous solution is placed between the metal surface and the cathode. By applying jet pressure to an electrolytic solution mixed with insulating hard particles, such as glass particles, and jetting it toward the contaminated metal surface, the contaminated metal surface is dissolved by electrolytic polishing action, and the insulating hard particles collide. This is a metal surface polishing device that uses the impact force of time to remove deposits on the contaminated surface and oxide film formed by electrolytic action. In addition, a cathode facing parallel to the metal surface, a current power source that sends a direct current to the metal surface and the cathode, respectively, and a high-pressure air source that applies jet pressure to the neutral inorganic salt aqueous electrolyte containing insulating hard particles. and a honing process in which the electrolytic solution to which ejection pressure is applied from the high-pressure air source is directed toward the metal surface and injected between the cathode and the metal surface.
This is a metal surface polishing device characterized by comprising a gun.

According to the present invention, the contaminated metal surface can be efficiently dissolved by electrolytic polishing, and since the electrolytic solution is a neutral inorganic salt aqueous solution, it is easy to handle. ! Since the electrolyte does not need to be neutralized, the generation of secondary waste can be reduced. Furthermore, since deposits and oxide films can be removed by spraying hard particles, pretreatment for electrolytic work is not necessary, and recontamination due to incorporation into the oxide film can be prevented.

[Embodiment of the Invention] Hereinafter, an embodiment of a metal surface polishing apparatus according to the present invention will be described with reference to FIG. In FIG. 1, reference numeral 1 denotes a metal to be treated, and a cathode 2 and a spray nozzle 3 are disposed so as to face the surface of the metal to be treated 1 and to penetrate through the center of the cathode 2.

The cathode 2 is connected to the negative electrode of a DC power source 4, and the positive electrode of the DC power source 4 is connected to the positive electrode by pressing the anode contact portion 5 with an external force through the anode contact portion 5 placed on the surface of the metal to be treated 1. It is electrically connected to the surface of the metal to be processed 1. The cathode 2 and the surface of the metal to be treated 1 are electrically insulated by an insulator 6. The injection nozzle 3 is connected to the electrolyte storage tank 7
The reservoir 417 is connected to the electrolyte supply tank 9 and the electrolyte recovery tank 10 through the pressurized supply pump 8 .

The metal surface polishing apparatus according to the present invention configured as above first applies the following steps to the surface of the radioactive metal 10 to be polished and decontaminated.
The anode contact portion 5, cathode 2, and injection nozzle 3 are installed at predetermined positions. Next, an electrolyte solution in which insulating hard particles, such as glass particles or ceramic particles are mixed into an aqueous solution of a neutral inorganic salt such as NaNOs, NaN0z, NaZ, or SO4, is passed from an electrolyte supply tank 9 through a pressurized supply pump 8 to an electrolyte reservoir. It is sent to a tank 7 and further sprayed onto the surface of the metal to be treated 1 from the spray nozzle 3. At the same time, the metal to be treated 1 and the cathode 2 are connected by the DC power supply 4.
When a voltage is applied to each, a current flows through the electrolytic solution, and the surface of the metal to be processed 1 is electrolytically polished.

Then, the radioactive cladding adhering to the surface of the metal to be processed 1 is removed by the collision of the hard particles. Subsequently, the contaminant layer on the inner surface of the metal to be treated is removed by electrolytic polishing. Note that the passive oxide film generated by electrolytic action is removed by collision with hard particles. Thereafter, the removed radioactive cladding, grinding powder of the contaminated layer, etc. are washed away with the electrolytic solution and collected in the collection tank 10. Therefore, the radioactive cladding and the inner surface contamination layer are removed from the metal 1 to be treated, and the radioactivity level is reduced to the i-control level of the natural world, so-called background level, and it can be handled in the same way as general waste. Next, the results of an experiment conducted to confirm the effects of the above embodiment will be explained with reference to FIG. In FIG. 2, curve a shows only electrolytic polishing, curve 2 shows a combination of blasting and electrolytic polishing, and horizontal line C shows the background. Note that the vertical axis shows the amount of surface contamination, and the horizontal axis shows the grinding time in arbitrary units. As is clear from FIG. 2, by combining plastic and electrolytic polishing, the polishing speed and polishing m can be increased, and the amount of surface contamination can be brought below the background level. Further, electrolytic polishing is performed by applying a voltage of 5 to 20 V between the cathode 2 and the metal to be processed 1 and passing a current at a current density of 0.5 to 2.5 A/cm 2 . The grinding time is appropriately selected depending on the depth into which the radioactive substance has penetrated into the metal crystal structure and the degree of surface contamination determined by its concentration. After decontamination to a predetermined radioactivity level, the cathode 2
Then, the injection nozzle 3 and the anode contact part 5 are moved to another location and reinstalled, and the decontamination work is repeated. The electrolyte is NaN0aN
An aqueous solution containing 5 to 30ii1% of at least one selected from aNO2 or NazS04 is used.

In addition, in order to improve current efficiency NaF may be added in an amount of 0.1 to 2.50/L.

The insulating hard particles are suitably glass particles such as soda-lime glass, or ceramic particles such as aluminum oxide, but other materials may also be used.

In the above embodiments, the case where the electrolytic solution is disposable has been described, but it may be recovered from the recovery tank 10 by the pump 8 and used for circulation.

[Effect of the invention] As described above, the present invention uses the metal to be decontaminated as an anode,
The cathode was placed parallel to the metal surface and faced before.

2 Electrolytically polish the surface of the metal to be treated by applying injection pressure to an electrolytic solution containing insulating hard particles mixed in a neutral inorganic salt aqueous solution between the metal to be treated and the cathode and spraying it toward the metal surface to be treated. It is also a metal surface polishing device that uses the impact force generated when insulating hard particles collide to remove deposits and passivating oxide films produced by electrolytic action. Therefore, according to the present invention, since deposits and passivating oxide films can be removed by spraying 11iP particles, electrolytic polishing can be carried out efficiently, and the radioactivity level of radioactive metal waste can be lowered to the background level. It has remarkable effects, such as the ability to handle solid radioactive waste in the same way as general waste.

In particular, compared to when only blasting is used, the grinding speed is increased by more than 10 times, there is no limit to the grinding depth, it is easy to control, and the amount of wear on the grinding object is less than half. In addition, even a neutral inorganic salt as an electrolytic solution can sufficiently produce an electrolytic polishing effect, and is safe and easy to handle.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the invention. FIG. 2 is a diagram showing the relationship between polishing time and reduction in surface contamination amount. 1... Metal to be treated 2... Cathode 3... Injection nozzle 4... DC power supply 5... Anode connection part 7... Electrolyte storage tank 8... Pressurized supply pump
9... Electrolyte supply tank application agent Patent attorney Gobe Kikuchi

Claims (4)

[Claims] (1) An anode contact part for making the metal to be treated an anode;
A cathode provided facing the metal to be treated, a DC power source for applying a voltage between the two electrodes, and an injection nozzle for injecting an electrolytic solution to the metal to be treated through the cathode. A metal surface polishing device characterized by: (2) The metal surface polishing apparatus according to claim 1, wherein the electrolytic solution is an aqueous solution of a neutral inorganic salt mixed with insulating hard particles. (3) The insulating hard particles are soda lime glass or aluminum oxide, the neutral inorganic salt is at least one selected from sodium nitrate, sodium nitrite, and sodium sulfate;
3. The metal surface polishing device according to claim 2, wherein the metal surface polishing device has a melt content of ˜30% by weight. (4) The metal surface polishing apparatus according to claim 1, wherein an electrolytic solution storage tank and a pressurized supply pump are connected to the downstream side of the injection nozzle.