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Studies of radionuclide sorption by clays in the Culebra Dolomite at the WIPP (Waste Isolation Pilot Plant) site, southeastern New Mexico
In the most transmissive parts of the Culebra Dolomite, fluid flow is controlled by fractures. Gypsum (CaSO{sub 4} 2H{sub 2}O) and corrensite (a mixed chlorite/smectite) are the most abundant fracture-fill minerals. Radionuclide/clay interactions may be the dominant mechanism for radionuclide retardation. For this reason, the focus of this study is to examine the extent of the sorption of uranium and plutonium onto clays within the Culebra matrix and fractures. This paper describes several coordinated activities which will evaluate the potential retardation of radionuclide migration by sorption onto clays within the Culebras. These include characterization of the compositions of clays and groundwaters along the flow path; studies of the surface properties of simple reference clays and Culebra clays in dilute solutions and saline mixed electrolytes; development of a database of intrinsic equilibrium constants and specific-interaction parameters for calculations of the aqueous speciation of uranium and plutonium in Na-Cl-Ca-SO{sub 4}-CO{sub 3}-EDTA solutions which range in ionic strength from 0.1--4.0 molal; and measurement of surface complexation constants for uranium and plutonium in simple and mixed electrolyte solutions containing clays. 2 refs., 2 figs.