CS277470B6 - Electrolyte for semi-dry electrochemical decontamination of metal surfaces - Google Patents

Abstract

The electrolyte contains 0.1 to 1 weight percent of aniline-2,5-disulfonic acid, 1 to 2 weight percent of oxalic acid, 1 to 3 weight percent of ammonium nitrate and is made up to 100 weight percent with water.

Description

Technical field

The invention relates to an electrolyte intended for the semi-dry electrochemical decontamination of metal surfaces of equipment and parts thereof contaminated during the operation of a nuclear reactor, in particular for making them accessible to defectoscopic tests.

Semi-dry electrochemical decontamination of metallic materials is widely used in the operation of nuclear power plants. Mixed acid solutions are used as electrolytes, such as a solution composed of 1 to 40 weight percent sulfuric acid and 3 to 50 weight percent phosphoric acid and 0 to 5 weight percent oxalic acid supplemented to 100 weight percent with water. Next, a mixture of 3 to 5 weight percent oxalic acid and 0 to 3 weight percent citric acid made up to 100 weight percent with water. Optionally, solutions of other substances such as nitric acid, sodium sulfate, sodium hydroxide, aluminum sulfate, acetic acid and the like.

The disadvantage of these solutions is the use of inorganic acids, especially sulfuric, nitric or phosphoric acid, often in too high concentrations, which has an adverse corrosive effect on the treated metal surface, on the materials of the application means (working electrode, tampon), resp. the demands on the treatment of liquid radioactive waste are increasing.

In solutions containing oxalic acid alone, ferrous oxalate occasionally precipitates and thus the decontaminated surface is recontaminated. Repeated use of electrolytes with a high content of oxalic acid (3 to 5 weight percent) in semi-dry electrochemical decontamination results in a gradual deterioration of the quality of the treated surface, which is associated with an increasing degree of recontamination and deterioration of surface decontamination.

Another disadvantage is the intensive formation of decomposition gases on the electrodes during electrolysis, which significantly burdens the working environment with radioactive aerosols.

The essence of the invention

The above-mentioned disadvantages are eliminated in the electrolyte according to the invention, which consists in 0.1 to 1% by weight of aniline-2,5-disulfonic acid, 1 to 2% by weight of oxalic acid dihydrate and 1 to 3% by weight of ammonium nitrate. . The remainder up to 100 weight percent is water.

The advantage of the electrolyte according to the invention is the elimination of negative corrosion on the processed metallic materials during long-term use of dry electrochemical decontamination, further achievement of high decontamination efficiency at relatively low concentration of electrolyte components - maximum 5 wt.

CS 277470 B6 2 percent and a significant reduction in the formation of decomposable electrolytic gases. When using the electrolyte according to the invention, the intensity of flue gas formation decreased by 75% compared to the electrolyte known and used hitherto. '

Example of an embodiment of the invention

The electrolyte according to the invention was applied in a composition of 0.5 units by weight of aniline-2,5-disulfonic acid, 2 units by weight of oxalic acid dihydrate, 2 units by weight of ammonium nitrate and made up to 100 units by weight. with water. The electrolyte thus prepared was used in the semi-dry electrochemical decontamination of the surfaces of the reactor nozzles of the WER-440 type with the following results: decontamination factors DF = 150 to 470, no metallographic observations were found. adverse effect of the decontamination method used on the treated surfaces of the reactor nozzles. During electrolysis, a lower formation of gaseous products and aerosols was observed compared to the electrolytes used so far.

Industrial usability.

The electrolyte in the composition according to the invention is usable mainly in the semi-dry decontamination of nuclear power plant equipment.

Claims (1)

CS 277470 B6 has a substantial reduction in decomposition electrolytic gases. Using the electrolyte of the present invention, the gaseous effluent intensities decreased by 75% over the known and used electrolytes. DETAILED DESCRIPTION OF THE INVENTION The electrolyte of the present invention was applied in the composition of 0.5 weight units of aniline-2,5-disulfonic acid, 2 weight units of oxalic acid - dihydrate, 2 weight units of ammonium nitrate and supplemented to 100 weight percent with water. The electrolyte thus prepared was used in semi-dry electrochemical decontamination of the WER-440 reactor sleeve surfaces with the following results: decontamination factorsDF = 150-470, no metallographic observations showed any adverse effect of the decontamination method used on the treated reactor sleeve surfaces. During electrolysis, the formation of gaseous products and aerosols was observed to be lower than previously used electrolytes. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrolyte in the composition of the present invention is mainly applicable to dry decontamination of core power plants. PATENTAL REQUIREMENTS Electrolyte for semi-dry electrolytic decontamination of metal materials, characterized in that it contains 0.1 to 1% by weight aniline-2,5-disulfonic acid, 1 to 2% by weight of stearic acid dihydrate, 1 to 3 % by weight of ammonium nitrate, the remainder to 100 weight percent being water. End of document