Yucca mountain project: argonne national laboratory, annual progress report, fy211 1997 for activity wp 1221 unsaturated drip condition testing of spent fuel and 211 unsaturated dissolution tests of glass

摘要

This document reports on the work done by the Nuclear Waste Management Section of211u001ethe Chemical Technology Division of Argonne National Laboratory in the period of 211u001eOctober 1996 through September 1997. Studies have been performed to evaluate the 211u001ebehavior of nuclear waste glass and spent fuel samples under the unsaturated 211u001econditions (low-volume water contact) that are likely to exist in the Yucca 211u001eMountain environment being considered as a potential site for a high-level waste 211u001erepository. Tests with actinide-doped waste glasses, in progress for over 11 211u001eyears, indicate that the transuranic element release is dominated by colloids 211u001ethat continuously form and span from the glass surface. The nature of the 211u001ecolloids that form in the glass and spent fuel testing programs is being 211u001einvestigated by dynamic light scattering to determine the size distribution, by 211u001eautoradiography to determine the chemistry, and by zeta potential to measure the 211u001eelectrical properties of the colloids. Tests with UO(sub 2) have been ongoing for 211u001e12 years. They show that the oxidation of UO(sub 2) occurs rapidly, and the 211u001eresulting paragenetic sequence of secondary phases forming on the sample surface 211u001eis similar to that observed for uranium found in natural oxidizing environments. 211u001eThe reaction of spent fuel samples in conditions similar to those used with 211u001eUO(sub 2) have been in progress for over six years, and the results suggest that 211u001espent fuel forms many of the same alteration products as UO(sub 2). With spent 211u001efuel, the bulk of the reaction occurs via a through-grain reaction process, 211u001ealthough grain boundary attack is sufficient to have reacted all of the grain 211u001eboundary regions in the samples. New test methods are under development to 211u001eevaluate the behavior of spent fuel samples with intact cladding: the rate at 211u001ewhich alteration and radionuclide release occurs when water penetrates fuel 211u001esections and whether the reaction causes the cladding to split. Alteration phases 211u001ehave been formed on fine grains of UO(sub 2) in contact with small volumes of 211u001ewater within a several month period when the radiolysis product H(sub 2)O(sub 2) 211u001eis added to the groundwater solution. The test setup has been mocked up for 211u001eoperation with spent fuel in the hot-cell.