Used fuel disposition in crystalline rocks (original) (raw)

established the Used Fuel Disposition Campaign (UFDC) in fiscal year 2010 (FY10) to conduct the research and development (R&D) activities related to storage, transportation and disposal of used nuclear fuel and high level nuclear waste. The Mission of the UFDC is To identify alternatives and conduct scientific research and technology development to enable storage, transportation and disposal of used nuclear fuel and wastes generated by existing and future nuclear fuel cycles. The work package of Crystalline Disposal R&D directly supports the following UFDC objectives:  Develop a fundamental understanding of disposal system performance in a range of environments for potential wastes that could arise from future nuclear fuel cycle alternatives through theory, simulation, testing, and experimentation.  Develop a computational modeling capability for the performance of storage and disposal options for a range of fuel cycle alternatives, evolving from generic models to more robust models of performance assessment. Used Fuel Disposition in Crystalline Rocks vi 9/21/2016 us to simulate U(VI) adsorption onto Na-montmorillonite over a wide range of chemical solution conditions with a lower number of fitting parameters than previous SCM concepts, and without including a second site type or the formation of ternary U(VI)-carbonato surface complexes. This SCM allows us to simulate U(VI) sorption onto montmorillonite as a function of chemical solution conditions, while minimizing the number of fitting parameters in subsequent uranium(VI) diffusion models. Modeling results suggest that an accurate description of the unique characteristics of electrostatic surface potentials on montmorillonite edge sites is highly important, in order to accurately predict U(VI) sorption and transport behavior at larger field scales. Similar modeling approaches may also be useful for other charge-unbalanced, layered mineral phases. Our modeling results further emphasize the strong influence of dissolved carbonate ligands on U(VI) sorption, which is driven by the competition between U(VI)-carbonate complexation reactions in solution and U(VI) surface complexation reactions on montmorillonite edge sites. • Colloid-Facilitated Radionuclide Transport: A comprehensive literature review and data synthesis has been conducted on colloid-facilitated radionuclide transport (CFRT), and a scheme for the implementation of the CFRT model in performance assessment has been proposed (the results are reported in a separated report). A comprehensive model interpretation has been performed for the Grimsel Test Site (GTS) CFRT tests, yielding valuable insights for modeling of radionuclide transport, and particularly of CFRT, in saturated fractured crystalline rocks. It is shown that the actinides Th, Pu and Am, and the fission product 137 Cs, are the most likely radionuclides to experience colloid-facilitated transport over long time and distance scales (at least for bentonite colloids in a fractured crystalline setting). However, the time and distance scales of the GTS tests were very short relative to time and distance scales of relevance for nuclear waste repository performance assessments, so it should not necessarily be concluded that colloid-facilitated transport of these radionuclides will be a concern in such performance assessments. The GTS results collectively suggest that CFRT is likely to be more efficient at lower radionuclide concentrations than at higher concentrations because a greater fraction of the radionuclide mass will then tend to become associated with strong, low abundance adsorption sites on the colloids.