Application of Nuclear Magnetic Resonance to the Study of Nuclear Waste Relevant Molybdates at Ambient and High Temperatures
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Date
2014-01-15
Authors
Wren, John Edwin Christopher
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Abstract
High-Level Waste (HLW), contains radioactive isotopes with half-lives upwards of millions of years. The long-term storage of HLW can be accomplished through vitrification of the mixture in a borosilicate melt, producing a chemically inert solid. Unfortunately, molybdates can precipitate from the glass melt as water- soluble oxides containing radionuclei. Part of this study is dedicated to the characterization and interpretation of the NMR parameters for a series of crystalline molybdate phases at ambient temperatures. 23Na, 95Mo and 133Cs MAS NMR data were correlated to the local structure and geometry, showing several key trends. From the ambient temperature studies, select crystalline phases were chosen for high-temperature experiments up to 700◦C. These experiments were used to characterize the behaviour of these phases at temperatures relevant to both the formation of solid waste forms and their long-term storage. With these spectral “fingerprints”, it is possible to monitor the phase separation behaviour at temperatures relevant to vitrification and long-term geological storage. For example, the conversion of CsNaMoO4·2H2O into Cs3Na(MoO4)2 and Na2MoO4 can be followed in situ through MAS NMR. Finally, a series of model nuclear waste glasses with varying amounts of Cs and Mo were studied, allowing direct observation of the crystallization process.
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Keywords
NMR, Nuclear, Waste, Inorganic