Studies of radionuclide sorption by clays in the Culebra dolomite at the WIPP site, southeastern New Mexico

The ability of radionuclide-rock interactions to retard the migration of plutonium and uranium within clay-lined fractures in the Culebra Dolomite Member of the Rustler Formation is being estimated in support of the performance assessment of the Waste Isolation Pilot Plant. This paper describes progress in three coordinated studies: (1) characterization of the properties of the groundwater and minerals in the Culebra that will control radionuclide retardation; (2) development of a thermodynamic model for the adsorption of uranium onto corrensite, the mixed chlorite-smectite clay mineral found in Culebra fractures; and (3) development of a database of equilibrium constants and interaction parameters for calculations of the aqueous speciation of uranium and plutonium in Na-Cl-Ca-SO4-CO3 solutions which contain organic ligands such as EDTA and range in ionic strength from approximately 0.8 - 6.0 molal. 22 refs., 6 figs., 1 tab