Remediation and closure of the Single-Shell Tanks (SSTs) located on the Department of Energy's Hanford Site may depend on innovative waste removal, pretreatment and disposal technologies. This report describes preliminary studies conducted to support pretreatment processing of SST waste. This presentation looks specifically at the following types of activities: development, synthesis and characterization of a nonradioactive simulated SST waste; preliminary sequential dissolutions of simulated tank sludge; and thermochemical reduction of nitrate, a major component in SST waste. 7 refs., 4 figs., 6 tabs.

Radioactive waste is stored in 149 3,785 m3 (million gal) single-shell tanks on the US Department of Energy's Hanford Reservation in eastern Washington. To minimize leakage as the tanks age, the free liquid has been pumped out, leaving concentrated solidified salt cake and sludge deposits. Now methods to dislodge and remove this waste are being developed so that the waste can be retrieved and processed for permanent storage. This paper presents research and development on ultrahigh-pressure water-jet technology to fracture and dislodge the wastes in these tanks. A water-based prototype scarifier with an integral conveyance system is being developed, and its performance demonstrated in a coupled analytical and experimental investigation. This paper describes experimental objectives and approach and results of the single jet experiments. Previous testing indicates that the method can be readily applied to salt cake waste forms; retrieval and conveyance of sludge and viscous fluid waste forms may present additional challenges.

Significant progress has been made on the Hanford single shell tank (SST) retrieval projects since they were initiated as part of the modified Hanford Federal Facility Agreement and Consent Order (Tri-party Agreement) in 2000. Four of the 149 SSTs at the U.S. Department of Energy (DOE) Office of River Protection (ORP) Hanford facility are being retrieved to meet Tri-Party Agreement commitments. An additional tank is being retrieved to demonstrate an alternate technical approach. As the Hanford Site transitions to an accelerated retrieval and closure mission, these methods will be the baseline methods for SST retrieval. The five SSTs are located within the Hanford 200- Area tank farms operated by CH2M HILL Hanford Group (CH2M HILL) for ORP. Included in this paper will be discussions on the technologies selected for retrieval of each tank; electrical resistance technologies that are being evaluated for ex-tank leak detection and monitoring; and the Cold Test Training Facility (CTTF) used for testing of and training on the different retrieval systems.