Transient melt formation and its effect on conversion phenomena during nuclear waste vitrification HT-ESEM analysis

0575289 - ÚSMH 2025 RIV US eng J - Článek v odborném periodiku
Pokorný, Richard - Vernerová, Miroslava - Kloužek, Jaroslav - Cincibusová, Petra - Kohoutková, M. - Pezl, R. - Ferkl, P. - Hrma, P. - Podor, R. - Schuller, S. - Kruger, A.A.
Transient melt formation and its effect on conversion phenomena during nuclear waste vitrification HT-ESEM analysis.
Journal of the American Ceramic Society. Roč. 107, č. 3 (2024), s. 1691-1705. ISSN 0002-7820. E-ISSN 1551-2916
Institucionální podpora: RVO:67985891
Klíčová slova: glass melting * molten salt * nuclear waste * scanning electron microscopy * segregation * volatilization
Obor OECD: Ceramics
Impakt faktor: 3.9, rok: 2022
Způsob publikování: Open access
https://doi.org/10.1111/jace.19361

Although the vitrification of nuclear waste has a decades-long history, numerous opportunities still exist to improve its efficiency and to increase the waste loading in glass. This is especially true for the vitrification of low-activity waste (LAW), which has been historically treated by other immobilization technologies and is less mature than high-level waste (HLW) vitrification. In this work, we address one of the least understood phenomena during the conversion of nuclear waste feeds to glass-the formation of molten salt and transient glass-forming melt. Using high-temperature environmental scanning electron microscopy (HT-ESEM) in combination with X-ray diffraction, thermogravimetry, and evolved gas analysis, we have analyzed the complex chemical reactions and phase transitions as they occur during melting of representative HLW and LAW melter feeds. We evaluated the compositions of amorphous phases and the fractions of salt components, and estimated the fractions of molten salt phases present in the feeds as a function of temperature. We show that the maximum fraction of molten salts is & SIM,4 % and & SIM,28 % during HLW and LAW feed melting, respectively, and discuss the possibility of molten salt migration in LAW feeds. We also argue that the presence of significant fractions of molten salt phase can hinder the retention of rhenium (and, hence, radioactive technetium), and discuss how the properties of molten salt phase and transient glass-forming melt are related to primary foam formation and behavior. Finally, we summarize key unanswered questions requiring further research to increase the understanding of the conversion process and enhance the nuclear waste vitrification efficiency.
Trvalý link: https://hdl.handle.net/11104/0353630