HR: 1340h
AN: V23A-1246 [WITHDRAWN]    [Abstracts]
TI: Surface Complexation Modeling of Radionuclide Sorption in the Saturated Zone of Yucca Mountain Rocks
AU: * Ding, M
EM: mding@lanl.gov
AF: Los Alamos National Laboratory, MS J514, Los Almaos, NM 87545,
AU: Kelkar, S
EM: kelkar@lanl.gov
AF: Los Alamos National Laboratory, MS J514, Los Almaos, NM 87545,
AU: Fabryka-Martin, J
EM: fabryka@lanl.gov
AF: Los Alamos National Laboratory, MS J514, Los Almaos, NM 87545,
AU: Caporuscio, F
EM: floriec@lanl.gov
AF: Los Alamos National Laboratory, MS J514, Los Almaos, NM 87545,
AU: Meijer, A
AF: GCX Inc., 1389 E. Stoney Canyon Cr., Tuscon, AZ 85737,
AB: The U.S. DOE is preparing to submit a license application to the Nuclear Regulatory Commission (NRC) to create a geologic repository at the Yucca Mountain, Nevada, for the disposal of spent nuclear fuel and high-level radioactive waste. In the event of a radionuclide release, the ground water beneath the Yucca Mountain is the primary medium through which most radionuclides might move from the geologic repository to the accessible environment. Sorption of radionuclides onto rock surfaces in the saturated zone of Yucca Mountain (SZ) is one of the most important processes retarding their release to the accessible environment. For this reason, a considerable experimental effort has been devoted over the last two decades to the measurements of sorption distribution coefficients (Kd) for various radionuclides in rock samples from the vicinity of the repository site at the Yucca Mountain. Despite the quantity and quality of the data, they are strictly valid only under the experimental conditions at which they were measured, whereas the Kd distributions used as inputs in performance assessment calculations need to represent the range of geochemical conditions and rock types expected to occur along the transport pathways. Hence geochemical modeling was used to calculate and predict chemical speciation of elements of interest in solid and solution under a variety of different conditions. The computer code PHREEQC v2.3 and the thermodynamic database PHREEQCDATA025.DAT were used for this geochemical modeling. The modeling provides a basis for extrapolating the experimentally derived Kd's, and provides improved understanding of the underlying sorption mechanisms, thus justifying and defending the Kd's selected for further radionuclide transport modeling development. This presentation focuses on the elements Am, U, Np and Pu which sorb in the SZ primarily via surface complexation reactions. We discuss quantitatively the influence of groundwater compositions, rock surface area, binding constants, and thermodynamic data on the sorption of the above mentioned radionuclides onto the minerals commonly present in the Yucca Mountain geologic setting. In addition, calculated sorption parameters are compared with the results of experimental data. The site specific probability distributions for Kd's selected as inputs to the numerical transport model of site-scale saturated zone beneath the Yucca Mountain are also presented.
DE: 3610 Geochemical modeling (1009, 8410)
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 4807 Chemical speciation and complexation
DE: 4860 Radioactivity and radioisotopes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting