SORPTION/DESORPTION BEHAVIOR OF URANIUM IN YUCCA MOUNTAIN ALLUVIUM

Yucca Mountain, Nevada is currently being studied as the designated geological repository for high-level nuclear waste in the United States. The saturated alluvium located south of Yucca Mountain is expected to serve as a natural barrier to the migration of ²³³U(VI) in the event engineered barriers fail. The purpose of our study is to evaluate the saturated alluvium as a natural barrier to ²³³U(VI). Sorption and desorption studies of ²³³U(VI) onto alluvium obtained from Nye County wells located south of Yucca Mountain were conducted, with particular emphasis on investigating the distribution of uranium desorption rates from the alluvium over long periods of time. Our results indicate a wide distribution of desorption rates for ²³³U(VI), suggesting that alluvium has multiple types of active sorption sites with different affinities for uranium. While a significant fraction of the initially-sorbed uranium desorbed from the alluvium quite rapidly, a roughly equivalent amount remained sorbed after several months of testing. The information obtained through this research suggests that uranium may experience greater effective retardation in the alluvium than simple batch sorption experiments would suggest.