An investigation of metallic uranium corrosion in a Geological Disposal Facility (GDF) setting.

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Geological disposal is internationally recognised as the safest long-term solution for higher activity radioactive wastes and the UK's legacy wastes, including those containing uranium metal, are intended to be managed in this way. The current PhD project will investigate the corrosion behaviour of unirradiated Magnox uranium metal, under conditions analogous to a Geological Disposal Facility (GDF) both (i) pre-closure and (ii) post-closure. The project will also seek to conduct analysis of micro-samples of reactor-irradiated uranium to determine if corrosion rates are closely comparable to those derived from unirradiated metal.This study aims to better underpin the expected behaviour of metallic uranium following disposal in a GDF. It is expected that any residual uranium metal present in an Intermediate Level Waste (ILW) package will be encased in either grout or sludge but there is the potential for raw waste storage in self-shielded boxes; which would mean that 'carry-over' uranium in the raw waste, which is already part-corroded, could directly contact groundwaters in a GDF. Accordingly the study will examine the corrosion behaviour of uranium under water at high pH and carbonate content whilst (i) naked and part-corroded, and in comparison to (ii) U encased in grout and (iii) entrapped in Mg(OH)2 sludge. The primary focus would be on unencapsulated uranium corrosion in water chemistries analogous to a GDF environment and would include studies of gas release rates under these conditions as well as the pH transition from pond-water chemistry to GDF water chemistry. This is an area of research yet to be studied in any detail.