Evaluation of ²³⁵U Isotopic Dilution with the Addition of Depleted Uranium to Supernatant Liquid Waste

Laboratory-scale results on experiments performed to examine the feasibility of isotopic dilution of ²³⁵U in supernatant liquid storage tanks at the Savannah River Site are described. The isotopic dilution tests were accomplished by adding an alkaline depleted uranium solution to small portions of simulated and actual storage tank waste solutions with enriched ²³⁵U compositions. Based on the laboratory observations, recommendations were made, which involved the addition of significant quantities of uranyl carbonate solution to more than 4 million l of ²³⁵U enriched waste stored in tank 43H at the site to reduce the risk for criticality.

A post-uranyl carbonate addition analysis on the tank supernate confirmed the effectiveness of depleted uranium in isotopic dilution of ²³⁵U. The ²³⁵U enrichment in tank 43H was isotopicaly diluted from an original high of >4 wt% down to <0.5 wt%, as predicted from the laboratory investigations.