Approach for tank safety characterization of Hanford site waste

The overall approach and associated technical basis for characterizing Hanford Site waste to help identify and resolve Waste Tank Safety Program safety issues has been summarized. The safety issues include flammable gas, noxious vapors, organic solvents, condensed-phase exothermic reactions (ferrocyanide and organic complexants), criticality, high heat, and safety screening. For the safety issues involving chemical reactions (i.e., flammable gas, organic solvents, ferrocyanide, and organic complexants), the approach to safety characterization is based on the fact that rapid exothermic reactions cannot occur if either fuel, oxidizer, or temperature (initiators) is not sufficient or controlled. The approach to characterization has been influenced by the progress made since mid-1993: (1) completion of safety analyses on ferrocyanide, criticality, organic solvent in tank 241-C-103, and sludge dryout. (2) successful mitigation of tank 241-SY-101; (3) demonstration of waste aging in laboratory experiments and from waste sampling, and (4) increased understanding of the information that can be obtained from headspace sampling. Headspace vapor sampling is being used to confirm that flammable gas does not accumulate in the single-shell tanks, and to determine whether organic solvents are present. The headspaces of tanks that may contain significant quantities of flammable gas will be monitored continuously using standard hydrogen monitors. For the noxious vapors safety issue, characterization will consist of headspace vapor sampling of most of the Hanford Site waste tanks. Sampling specifically for criticality is not required to confirm interim safe storage; however, analyses for fissile material will be conducted as waste samples are obtained for other reasons. High-heat tanks will be identified through temperature monitoring coupled with thermal analyses.