Laboratory stabilizations/solidification of tank sludges: MVST/BVEST

Oak Ridge tank sludges that have been collected over several decades are being combined for treatment and disposal. Stabilization of the highly radioactive, mixed-waste sludges in the different tank sets has been evaluated prior to the proposed combination and treatment. This paper documents the testing of a Melton Valley Storage Tank (MVST)/Bethel Valley Evaporator Storage Tank set. Subsequent papers will discuss continued work on other tank sets and efforts to maximize the sludge loading. Grout formulations were tested in the laboratory both with a surrogate and with a sample of an actual mixed waste tank sludge from MVST W-25. Wet-sludge loadings of 50-60wt% resulted in strong wasteforms with no free water and gave a volume increase of about 40-50vol%. Resource Conservation and Recovery Act (RCRA) metals included in the surrogate testing were cadmium, chromium, lead, selenium, thallium, and mercury. The actual sludge sample was only characteristically hazardous for mercury by the Toxic Characteristic Leaching Procedure but exceeded the Universal Treatment Standard (UTS) limit for chromium. The grout formulations stabilized these two RCRA metals within UTS limits. In addition, a grout leachability index of about 9.0-10.0 was measured for both (85)Sr and (137)Cs, meeting the recommended requirement of >6.0.