Characterization and leaching study of sludge from Melton Valley Storage Tank W-25

One of the greatest challenges facing the Department of Energy (DOE) is the remediation of the 100 million gallons of high-level and low-level radioactive waste in the underground storage tanks at its Hanford, Savannah River, Oak Ridge, Idaho, and Fernald sites. Bench-scale batch tests have been conducted with sludge from the Melton Valley Storage Tank (MVST) Facility at Oak Ridge National Laboratory (ORNL) to evaluate separation processes for use in a comprehensive sludge-processing flow sheet for concentrating the radionuclides and reducing the volumes of storage tanks wastes for final disposal. This report discusses the hot cell apparatus, the characterization of the sludge, and the results obtained from a variety of basic and acidic leaching tests of samples of sludge. Approximately 5 L of sludge/supernate from MVST W-25 was retrieved and transferred to a stainless steel tank for mixing and storage in a hot cell. Samples were centrifuged to separate the sludge liquid and the sludge solids. Air-dried samples of sludge were analyzed to determine the concentrations of radionuclides, other metals, and anions. Based upon the air-dried weight, about 41% of the centrifuged, wet sludge solids was water. The major alpha-, gamma-, and beta-emitting radionuclides in the centrifuged, wet sludge solids were {sup 137}Cs, {sup 60}Co, {sup 154}Eu, {sup 241}Am, {sup 244}Cm, {sup 90}Sr, Pu, U, and Th. The other major metals (in addition to the U and Th) and the anions were Na, Ca, Al, K, Mg, NO{sub 3}{sup {minus}}, CO{sub 3}{sup 2{minus}}, OH{sup {minus}}, and O{sub 2{minus}}. The organic carbon content was 3.0 {+-} 1.0%. The pH was 13