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Degradation of phosphatic waste forms incorporating long-lived radioactive isotopes

Published online by Cambridge University Press:  05 July 2018

D. Read  and
C. T. Williams
D. Read*
Affiliation:
Enterpris Ltd., University of Reading, Whiteknights, Reading, Berks RG6 6AB, UK
C. T. Williams
Affiliation:
Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK
*
*E-mail: enterpri@readinguni.u-net.com
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Abstract

This paper provides a brief perspective on synthetic, phosphate-based waste forms for high level radioactive waste (HLW). Evidence in support of their long-term stability is then discussed by reference to the degradation of natural monazites with emphasis on the fate of released uranium, thorium and the rare earths (REE). It is apparent that the REE can be mobilized and fractionated at temperatures anticipated in a HLW repository (∼200°C). This provides an indication of the likely fate of the trivalent actinides (Am(III), Cm(III)) if incorporated in similar matrices. Thorium, though released on alteration of monazite, tends to re-concentrate locally in secondary, microcrystalline phases. In relative terms, U is readily removed from monazites. Although it can be re-concentrated in alteration products, the potential exists for substantial loss of U to groundwater. The findings of this research have important implications for the performance of radioactive waste disposal systems where there is a clear need for improved chemical data to describe the precipitation-dissolution of phosphate phases. It is concluded that monazite-like ceramics designed for the containment of HLW will retain tetravalent actinides but may release uranium in response to natural degradative processes.

Keywords

phosphatic waste formsradioactive isotopesuraniumhigh-level radioactive waste
Type
Research Article
Information
Mineralogical Magazine , Volume 65 , Issue 5 , October 2001 , pp. 589 - 601
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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