Disposal of Hanford site tank wastes

Between 1943 and 1986, 149 single-shell tanks (SSTs) and 28 double-shell tanks (DSTs) were built and used to store radioactive wastes generated during reprocessing of irradiated uranium metal fuel elements at the U.S. Department of Energy (DOE) Hanford Site in Southeastern Washington state. The 149 SSTs, located in 12 separate areas (tank farms) in the 200 East and 200 West areas, currently contain about 1.4 x 105 m3 of solid and liquid wastes. Wastes in the SSTs contain about 5.7 x 1018 Bq (170 MCi) of various radionuclides including 90Sr, 99Tc, 137Cs, and transuranium (TRU) elements. The 28 DSTs also located in the 200 East and West areas contain about 9 x 104 m3 of liquid (mainly) and solid wastes; approximately 4 x 1018Bq (90 MCi) of radionuclides are stored in the DSTs. Important characteristics and features of the various types of SST and DST wastes are described in this paper. However, the principal focus of this paper is on the evolving strategy for final disposal of both the SST and DST wastes. Also provided is a chronology which lists key events and dates in the development of strategies for disposal of Hanford Site tank wastes. One of these strategies involves pretreatment of retrieved tank wastes to separate them into a small volume of high-level radioactive waste requiring, after vitrification, disposal in a deep geologic repository and a large volume of low-level radioactive waste which can be safely disposed of in near-surface facilities at the Hanford Site. The last section of this paper lists and describes some of the pretreatment procedures and processes being considered for removal of important radionuclides from retrieved tank wastes