Sr/TRU REMOVAL FROM HANFORD HIGH LEVEL WASTE

Abstract

The originally proposed removal process for strontium and transuranic species from 241-AN-102 and 241-AN-107 Hanford waste tank supernates was a co-precipitation method. In initial testing, the slurry formed during the strontium and ferric nitrate co-precipitant additions was not filterable. A series of statistically designed tests were performed to evaluate the variables responsible for this poor filterability. These tests also explored strategies to improve the associated decontamination efficiency of the treatment process. These tests revealed that filterability is negatively influenced by ferric ion added to co-precipitate actinide and lanthanide species. The concentrations of sodium and organic complexants were observed to influence decontamination of the supernate. Furthermore, the amount of at least one organic complexant was correlated to the poor filterability. The americium decontamination factors measured following the maximum iron nitrate addition were marginal at levels of precipitant addition that are of practical interest. Based on these results, alternative precipitation schemes were investigated. Reported here is the chosen replacement process, a permanganate precipitation process. A statistically designed series of experiments examined the relationship between three responses and five precipitation parameters. The three responses are precipitate filterability, strontium decontamination, and plutonium decontamination. The parameters varied were the initial sodium and hydroxide concentrations of the waste, and the amount of calcium, strontium, and permanganate introduced. The results reveal an optimum set of conditions for decontamination of strontium and plutonium as well as improved filterability.