Conceptual Model and Risk Assessment of Waste Package Evolution - 15643

A generic disposal facility model was created to mirror disposal of low-level radioactive waste in a humid environment. The standard waste package used is a painted and primed carbon steel box stacked four high and placed next to one another within the disposal facility, preventing outward deformations of individual boxes. Waste is placed in the facility in sections, and as each section is filled it is covered with a layer of natural soil. It was assumed that boxes are exposed to natural precipitation rates for approximately 12 months, reduced to natural background infiltration to simulate the soil cover, and dropping to 1% of background infiltration when the facility is filled and a water-shedding interim cover is installed. It was also assumed that each box retains its structural integrity at the time of disposal, with the exception of the top box, which has its lid collapse inward from the overlying soil cover. Waste packages experience different rates of corrosion, differential amounts of infiltration, and fill with liquid at different rates based on when and where they are placed in the facility. Using historical literature and DOE site reports, calculations were made to estimate a range of waste package failure outcomes. (authors)