UNDERSTANDING GEOCHEMICAL PROCESSES CONTROLLING COLLOID-FACILITATED TRANSPORT OF PLUTONIUM: FROM 10-INCH CORE EXPERIMENTS TO KILOMETER SCALE FIELD OBSERVATIONS
To better understand the mechanisms controlling colloid-facilitated transport of Pu, a series of fracture -flow laboratory experiments were conducted with soluble Pu and Pu pre-sorbed to mineral colloids. The radionuclide cocktail was injected in polished fractured volcanic tuff cores. The effluent was analyzed and autoradiography and secondary ion mass spectrometry was used to image the colloid-Pu-rock interactions. Experimental conditions employed mimic conditions expected for the kilometer scale transport of Pu observed downgradient from underground nuclear tests at the Nevada Nuclear Security Site (NNSS, formerly called NTS). In our experiments, ~30% more Pu was eluted through the fractures with the colloids compared to soluble Pu. The majority of Pu retained in the fractured volcanic tuff was associated with the various minerals in the altered volcanic tuff cores, but significantly more Pu was associated with the minor Mn and Fe oxides. Our efforts combining fracture transport experiments, flow cell sorption/desorption experiments, and field scale monitoring at NNSS are helping to elucidate the dominant processes that control colloid-facilitated transport.
Prepared by LLNL under Contract DE-AC52-07NA27344.