Nuclear Technology / Volume 117 / Number 3 / March 1997 / Pages 316-328
Technical Paper / Radioactive Waste Management
Redistribution of vitrified weapons-grade plutonium placed in the proposed Yucca Mountain repository is investigated based on the pure-colloid transport model for plutonium and the pure-solute transport model for plutonium, uranium, and boron. In the pure-colloid model, colloids carrying plutonium are assumed to settle out of groundwater in the fractures by floccu-lation. In the pure-solute model, 239Pu, 235U, and boron are transported through fractures by advection and diffuse into the rock matrix with sorption retardation. Both models show that 239Pu stays in the vicinity of the repository and decays there to 235U. All the 239Pu that originally exists in the repository reaches the bottom end of 200-m fractures as 235U. Boron spreads in the geologic medium during the glass leaching period and quickly disappears after the end of the leach time. Concentrations of 239Pu and 235U are found to be too small for autocatalytic criticality.