(162b) Hanford Sludge Washing for Aluminum and Phosphate Dissolution

The nuclear waste at the Department of Energy’s (DOE) Hanford site represents one of the single largest environmental cleanup efforts currently underway. Large volumes of highly radioactive waste, generated during past plutonium production operations, are stored in underground tanks on the Hanford site. Effective disposition of this waste will require processing the sludge to immobilize the waste via vitrification into a stable glass form for long-term disposal. Conceptual flowsheets have proposed settling of the solids in process vessels as a primary step in providing sludge to the vitrification facility. Wastes with high concentrations of aluminum and phosphate have been identified as particularly challenging to process and simultaneously make up the majority of insoluble components in the sludge. This presentation details low temperature dissolution studies of aluminum and phosphate sludge simulants in a variety of wash matrices mimicking potential retrieval operations. Slurry compositions were prepared to match difficult layers in sludge tank AN-106 in order to bound high phosphate/high aluminum operating conditions experienced during processing this tank. Empirical testing data were compared to modeled solubility limits to determine dissolution rates under various wash conditions as well as demonstrate sludge volume reduction capabilities. Removal of these components can significantly reduce (2x) the volume of high-level waste glass produced, decrease operating costs, and improve processing performance.