モリブデン酸溶融塩を用いた乾式再処理プロセスに関する研究 溶融Ｎａ２ＭｏＯ４中における酸化ウランの化学および電気化学挙動

Abstract

For the realization of dry reprocessing, an effective method for the decladding of spent oxide is necessary. We aim to develop a decladding process that integrates with dissolution using molybdate melt as the solvent. This melt possesses characteristics such as it can make actinide oxide such as uranium dioxide dissolve in a very short time without reacting with metal such as the cladding tube. It is necessary to clarify the chemical and electrochemical behaviors of uranium corresponding to the proposed process in this melt. In this study, gram-scale uranium experiments were carried out, and the reaction of the uranium in the melt was investigated. In Na2MoO4-Na2Mo2O7 melts under an inert gas atmosphere, uranium dioxide dissolves as Na4U(MoO4)4 without changing its oxidation valence. It was confirmed by XPS that the tetravalent uranium cation was oxidized by oxygen gas to hexavalent uranium cation in the melt. In the electrolysis process, it was clarified that no deposit was observed on a cathode at 750 degrees centigrade caused by the redissolution of the deposit. When the temperature of the melt was 700 degrees centigrade, the redissolution of the deposit was reduced. The granulated powder of UO2 was successsfully recovered on a cathode at 700 degrees centigrade.