High-priority Hanford Site radioactive waste storage tank safety issues: An overview

Abstract

High-activity radioactive waste has been stored in large underground storage tanks at the U.S. Department of Energy's Hanford Site in eastern Washington State since 1944. Since then, more than 227,000 m 3 (60 Mgal) of waste have accumulated in 177 tanks. These caustic wastes consist of many different chemicals. The waste forms include liquids, slurries, salt cakes, and sludges. A number of safety issues have been raised about these wastes, and resolution of these issues is a top priority of the U.S. Department of Energy. A waste tank safety program has been established to resolve these high-priority safety issues. This paper will deal with three of these issues. The issues described are the release of flammable vapors from single- and double-shell tanks, and the existence of organic chemicals and/or ferrocyanide ion-containing fuel-rich mixtures of nitrate and nitrite salts in single-shell tanks. Extensive management controls are employed to ensure that the tanks in question continue to be maintained a safe manner through issue resolution. In addition, comprehensive monitoring, characterization, and applied and basic research efforts have been initiated to support resolution of issues and to prevent creation of future problems associated with potentially incompatible wastes. The safety efforts will also support actions related to the planned retrieval and disposal of the wastes in these storage tanks. Such efforts will also provide the basis for safe near-future remediation of these tanks on an as-needed basis and will define the envelope of safety to support the disposal of all high-level waste in the Hanford Site tanks.