Oxidation behavior of UCl in LiCl-KCl eutectic salt under Ar-O atmosphere

Ar-O雰囲気下におけるLiCl-KCl共晶塩中のUClの酸化挙動

杉原 英幸; 坂村 義治*; 村上 毅*; 仲吉 彬  

Sugihara, Hideyuki; Sakamura, Yoshiharu*; Murakami, Tsuyoshi*; Nakayoshi, Akira

The electrorefining of used fast reactor metal fuel is performed under inert gas (argon) atmosphere. Uranium and plutonium are dissolved as trivalent chlorides (UCl and PuCl) in the LiCl-KCl molten salt in the electrorefiner. To clarify the oxidation behavior of the trichlorides by the atmospheric impurities (e.g., O) is important for reprocessing facility design including safety issues. This study explored the oxidation behavior of UCl in LiCl-KCl eutectic salt under Ar-O atmosphere using thermodynamic calculations and thermogravimetric and differential thermal analysis (TG-DTA). The TG-DTA curves obtained at O = 757, 1760 and 3750 ppm suggested the significant oxidation of UCl. The dominant oxidation reaction deduced from the weight increase rate was the formation of tetravalent chloride and oxychloride, which was supported by the results of thermodynamic calculation. The results at the high O concentration (O=3750 ppm) suggested the oxidation reaction succeeding the formation of tetravalent chloride and oxychloride. In addition, an endothermic peak was observed at about 253 C. It was assumed that a part of the salt including oxidation products was melted. No exothermic peak was observed at O = 77 ppm, and the DTA results showed the oxidation hardly progressed at O = 77 ppm. To clarify the chemical forms and solubilities of the oxidation products is the future work, as well as the oxidation behavior when mixtures of O and HO ingress.