Stability of plutonium(VI) in WIPP brine

The redox stability of plutonium (VI) in WIPP brine was investigated by monitoring the oxidation state as a function of time using a combination of absorption spectrometry, radiochemical counting and filtration. Studies were performed with Pu-239 and Pu-238 in four WIPP brines at concentrations between 10{sup {minus}3} and 10{sup {minus}8} M for durations as long as two years. Two synthetic brines, Brine A and ERDA-6, and two underground collected brines, DH-36 and G-Seep, were used. The stability of Pu(VI) depended on the brine composition and the speciation of the plutonium in that brine. When carbonate was present, a Pu(VI)-carbonate complex was observed that was stable. In the absence of carbonate, Pu(VI) hydrolytic species predominated which had a wide range of stability in the brines investigated. The results reported will help define the speciation of plutonium in WIPP brine and hence its potential for migration.