Electrochemical reduction behavior of simplified simulants of vitrified radioactive waste in molten CaCl2

• Published in: Journal of nuclear materials Vol. 503; pp. 290 - 303
• Main Authors: Katasho, Yumi, Yasuda, Kouji, Nohira, Toshiyuki
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2018
• Subjects: Electrochemical reduction; Molten salt; Potential−pO2− diagram; Vitrified radioactive wastes; Electrochemical reduction; Vitrified radioactive wastes; Potential−pO2− diagram; Molten salt
• ISSN: 0022-3115; 1873-4820
• DOI: 10.1016/j.jnucmat.2018.03.006

The electrochemical reduction of two types of simplified simulants of vitrified radioactive waste, simulant 1 (glass component only: SiO2, B2O3, Na2O, Al2O3, CaO, Li2O, and ZnO) and simulant 2 (also containing long-lived fission product oxides, ZrO2, Cs2O, PdO, and SeO2), was investigated in molten CaCl2 at 1103 K. The behavior of each element was predicted from the potential−pO2− diagram constructed from thermodynamic data. After the immersion of simulant 1 into molten CaCl2 without electrolysis, the dissolution of Na, Li, and Cs was confirmed by inductively coupled plasma atomic emission spectrometry and mass spectrometry analysis of the samples. The scanning electron microscopy/energy dispersive X-ray and X-ray diffraction analyses of simulants 1 and 2 electrolyzed at 0.9 V vs. Ca2+/Ca confirmed that most of SiO2 had been reduced to Si. After the electrolysis of simulants 1 and 2, Al, Zr, and Pd remained in the solid phase. In addition, SeO2 was found to remain partially in the solid phase and partially evaporate, although a small quantity dissolved into the molten salt. [Display omitted] •Two simplified simulants of vitrified waste were electrolyzed in molten CaCl2.•The dissolution of Na, Li, and Cs into molten CaCl2 was confirmed.•The main component, SiO2, was reduced to Si by the electrolysis of the glass.•Al, Zr, and Pd remained in the solid phase after the electrolysis.