Laboratory Testing of Bulk Vitrified Low-Activity Waste Forms to Support the 2005 Integrated Disposal Facility Performance Assessment

Abstract

SummaryThe Hanford Site in southeastern Washington State has been used extensively to produce nuclear materials for the U. S. strategic defense arsenal by the U. S. Department of Energy (DOE). A large inventory of radioactive and mixed waste has accumulated in 177 single-and double-shell tanks. Waste recovered from the tanks will be pre-treated to separate the low-activity fraction from the high-level and transuranic wastes. The low-activity fraction will be among the largest volumes of radioactive waste within the DOE complex and is one of the largest inventories of long-lived radionuclides planned for disposal in a low-level waste facility. Currently, the DOE Office of River Protection (ORP) is evaluating several options for immobilization of low-activity tank wastes for eventual disposal in a shallow subsurface facility at the Hanford Site. A significant portion of the waste will be converted into immobilized low-activity waste (ILAW) glass with a conventional Joule-heated ceramic melter. In addition to ILAW glass, DOE is considering a supplemental treatment technology; bulk vitrification (BV), to treat a portion of the low-activity waste (LAW). The use of a supplemental treatment technology is expected to accelerate the overall cleanup mission at the Hanford site by at least 35 years. CH2M Hill Hanford Group, Inc. A critical component of the development and testing strategy will be to provide estimates of radionuclide release rates from the engineered portion of the disposal facilities (source term). These data will be used for Subsurface Transport Over Reactive Multi-phases (STORM) simulations of the BV waste package. Documented in this report are data related to 1) kinetic rate law parameters for glass and refractory dissolution, 2) sodium (Na + )-hydrogen (H + ) ion exchange rate, 3) chemical reaction network of secondary phases that form in accelerated weathering tests, and 4) thermodynamic equilibrium constants assigned to these secondary phases for BV vitrified product. The kinetic rate law and Na + -H + ion exchange rate were determined from single-pass flow-through (SPFT) experiments. Product consistency (PCT) tests were used for accelerated weathering or aging of the glasses to determine a chemical reaction network of secondary phases that form. The majority of the thermodynamic data used in this data package were extracted from the thermodynamic database package provided with the geochemical code EQ3/6, version 8.0.Results from SPFT tests suggest that rate law parameters derived for BV glasses are comparable to those determined for WTP glass formulations. SPFT tests also were used to calculate a bounding release rate for the mullite castable refractory block (CRB). The presence of multiple mineral phases in and the uncertainty regarding the true reactive surface area of the CRB may have a significant effect on the reported rates. Therefore, we recommend that rate law parameters be developed for the pure mineral phases identified in the CRB. These results should be combined with literature values to...

Current Understanding and Remaining Challenges in Modeling Long‐Term Degradation of Borosilicate Nuclear Waste Glasses

“…The current hypothesis is that the precipitation of zeolites (such as analcime NaAlSi 2 O 6 ÁH 2 O) affects dissolution by affecting one or more of the previously described mechanisms. The precipitation creates a sink for silicon, reducing the concentrations of Si from solution, 94 which in turn either increases the driving force for glass corrosion (reduce Q/K) or destabilizes the PRI. The result is an increase in the dissolution rate in either case.…”