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ELECTROCHEMICAL RECOVERY OF Tc FROM SOLUTIONS ISSUING FROM SNF REPROCESSINGтезисы доклада
- Авторы: Volkov M.A., German K.E., Kuznetsov V.V.
- Сборник: Proceedings and selected lectures of the 10th International Symposium on Technetium and Rhenium – Science and Utilization,
- Серия: 1
- Том: 1
- Тезисы
- Год издания: 2018
- Место издания: Publishing House Granica, Moscow
- Первая страница: 182
- Последняя страница: 183
- DOI: 10.13140/RG.2.2.16240.30721
- Аннотация: A new electrochemical method for extracting technetium from solutions of radioactive waste and SNF is proposed. The electrolyte proposed for the electrochemical extraction of technetium makes it possible to selectively isolate from the technetium solution a highly oxidized state. Depending on the current density from the SNF and RW solutions, it is possible to isolate molybdenum in the form of metal oxide coatings. Such an approach should reduce the amount of waste to be disposed of. Key words: pertechnetate, extraction of technetium, reprocessing of spent nuclear fuel, acetate. Radiochemical reprocessing of spent nuclear fuel (SNF) includes dozens of technologies for processing both introduced into the industry and passing laboratory tests. They meet all safety requirements, give a high degree of separation of the target radionuclides contained in SNF and assume the disposal of radioactive waste (RW) in various forms. Industrially implemented processes of water-chemical SNF processing usually include dissolving the opened fuel in nitric acid and further purification by extracting TBP in hydrocarbon diluents [1]. Purification is focused primarily on the separation of uranium and plutonium. For some fission products (PD), including 99 Tc, separation methods have been developed, the improvement of which can make it a valuable product. After the extraction of U and Pu, the washing solutions contain tangible amounts of technetium, usually in a highly oxidized state. They are still connected with the first cycle of raffinate and sent for residue, vitrification and disposal. It is also possible to prepare targets for further transmutation [2]. Trace amounts of technetium compounds are found even in purified oxides of uranium and plutonium [3]. Technetium is a problem PD in the reprocessing of spent nuclear fuel, accumulating with an output of ≈ 6%. Methods of extracting it from solutions usually extraction or precipitation, electrochemically from the formed acid solutions of technetium is poorly isolated. The electrolyte proposed in 2016 for the electrodeposition of molybdenum coatings is also of interest for technetium compounds due to the similarity of their electrochemical behavior. Through electrolysis on iron, brass, copper and gold cathodes from electrolyte proposed in [4-6] metal oxide coating is deposited. The content of oxides in the coating depends on the metal concentration, temperature, current density, diffusion and additionally introduced into the electrolyte cations of heavy metals such as cesium and rubidium. The precipitation of technetium compounds is carried out only from its highest degree of oxidation due to the pronounced adsorption on the cathode surface, which is confirmed by the shape of the current versus time curves on a growing mercury drop during polarographic studies. The thermodynamic deposition of metallic Tc from aqueous solutions is possible, but preferably from electrolytes with low values pH ≤ 4, but the concentrated (3-5 M) acetate electrolyte proposed for the precipitation of molybdenum makes it possible to conduct precipitation from electrolytes with a pH ≥ 9, which is explained by the suppression of water dissociation reactions. The recommended value for ammonium acetate electrolyte is pH = 7. During the electroreduction of ammonium pertechnetate, a dense coating is formed on the surface of the cathode, which has a metallic luster. The current density needed to form a coating should not exceed 400mA / dm 2 , which allows long-term electrolysis of solutions without additional cooling of the mixture, which saves energy costs. Precipitation of Tc at elevated current densities leads to the formation of insoluble, dense precipitates on the cathode with low adhesion, but the rate of extraction of technetium from the solution increases proportionally. The metal 182
- Добавил в систему: Волков Михаил Александрович