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Computer simulations were performed to assess the performance of the waste-form-alone (WFA) design for the low-activity-waste (LAW) disposal system. In FY 1997, PNNL performed additional simulations for Lockheed Martin Hanford Company (LMHC) to address specific questions about the disposal. LMHC manages the Glass Performance Assessment Project for DOE. The objectives of the additional simulations were to demonstrate the impact of grid resolution, diffusion, fracture flow within the waste form, and consumption of water by the waste form. It was assumed that the waste form would be the only part of the engineered disposal system that inhibits radionuclide release, referred to as WFA assumption. All calculations were performed with the latest version of the STOMP (Subsurface Transport Over Multiple Phases) simulator. Multiple simulations of the WFA disposal were performed to identify parameter and conceptual model sensitivities. The corrosion rate, recharge rate, well interception factor, hydraulic properties, and hydraulic and retardation models were shown to be important. Diffusion was shown to be important for the gravel model of glass but not the soil model. The impact of temperature changes was discussed and determined to be negligible. Water consumption during corrosion was evaluated and found to have a minimal effect on the dosemore » calculations. Fracture flow within the glass was evaluated and found to have only a minimal effect on the dose calculations.« less |
