Feasibility study of alternative treatment methods for MVST supernatant at ORNL

The Melton Valley Storage Tanks (MVST) at Oak Ridge National Laboratory (ORNL) currently contain greater than 370,000 gal of liquid radioactive waste concentrate. This volume is approaching 100% of the available storage capacity. These liquids may be characterized as concentrated alkaline-nitrate solutions contaminated with mCi/L concentrations of 137Cs and lower levels of other radionuclides. Pretreatment of the liquid by clarification and filtration yields a supernatant requiring a decontamination factor (DF) of 300 for 137Cs and 150 for 90Sr for subsequent on-site disposal as a concrete monolith. Alternatives investigated for achieving these DFs may be broadly grouped as ion exchange, precipitation, and evaporation. Three specific treatment systems within each broad group were analyzed on the basis of achievable volume reduction, decontamination performance, implementability, and protection of workers and the environment. Nonregenerable ion exchange was selected on the basis of these criteria. This paper presents the rationale for this selection