FATE AND TRANSPORT OF RADIONUCLIDES AT YUCCA MOUNTAIN

Yucca Mountain (YM), Nevada has been considered as a permanent disposal repository of high-level nuclear wastes because of the low rainfall and infiltration rates, thick unsaturated zone, and other factors. Characterization studies for the high-level nuclear waste repository at YM have identified 237Np, 238U, and 239Pu as concerned radionuclides. In order to assess the potential contamination of those radionuclides, an understanding of their hydrologic and geochemical properties is needed (including the diffusion, dispersion, solubility, adsorption, surface complexation and aqueous speciation). In this study the PHREEQC program is used to calculate the chemical reaction speciation for radionuclides in the YM groundwater system. Numerical experiments are designed to evaluate how the solubility would affect the speciation calculation. Results will provide bases for the further simulation of coupled flow and radionuclide transport in the groundwater.