In the UK, the Sellafield site Waste Vitrification Plant (WVP) currently immobilises highly active liquors produced from reprocessing of spent nuclear fuel into a borosilicate glass. Future challenges for WVP include the washout of solids from the base of the waste storage tanks in preparation for decommissioning, which will result in high molybdenum feeds to the plant. Molybdenum has a low solubility in the standard alkali borosilicate frit used on WVP, but laboratory experimental work has led to the development of a new calcium borosilicate glass formulation which can incorporate up to 10 wt% molybdenum oxide without any detrimental phase separation. Vitrification of high molybdenum feeds using the new formulation has also been carried out, using non-active simulants, on the Vitrification Test Rig (VTR) which is a full scale working replica of a WVP processing line. This paper discusses the results of both the laboratory and full scale trials.
