Chemistry aspects of the hanford tank Waste Treatment and Immobilization Plant (WTP) criticality safety evaluation

The Hanford Tank Waste Treatment and Immobilization Plant (WTP) is under construction by Bechtel National, Inc. for the Dept. of Energy (DOE) Office of River Protection (ORP) and is designed to treat about 50 million gallons of mixed radioactive waste and immobilize it by vitrification into a glass matrix. Criticality safety during the processing of this waste is dependent upon the presence of absorbers to maintain subcriticality in both the liquid and solid phases of the waste. During processing, the waste will be subjected to a number of chemical processes that can cause a phase change of both the Pu and the absorbers relied upon to control the reactivity. The chemistry aspect of waste processing with respect to criticality safety is the subject of this paper. An important conclusion of this work is that the chemistry effects limit the potential for criticality safety adverse solid-to-liquid and liquid-to-solid phase transitions of the Pu and under situations where such transitions do occur, the absorbers will follow the Pu in sufficient amounts to ensure subcriticality. (authors)