Roger Seitz*, Savannah River National Laboratory ; Andrew Wallo, U.S. Department of Energy

Abstract: The United States Department of Energy (DOE) has more than 25 years of experience conducting and overseeing performance assessments (PAs) for low-level waste (LLW) and mixed LLW from on-going operations, decommissioning and environmental restoration activities. DOE considers performance assessments (PAs) as one contributor to defense-in-depth arguments for safe disposal of LLW. In a risk-informed, performance-based approach to PA, it is necessary to address the time frames over which PA results are sufficiently meaningful to be used for a strict determination of compliance (i.e., a time of compliance). DOE has taken the position that, for near-surface disposal, 1,000 years is an appropriate time of compliance, but the potential for peak impacts after that time need to also be addressed. From an implementation perspective, 1,000 years is considered as a transition in the interpretation of results from use as a quantitative, decision-maker (“yes or no” compliance) to an increasingly qualitative role informing decisions in conjunction with all of the other contributors to the safety basis. This position is based on a number of technical and policy considerations with a major factor being the decreasing quantitative meaningfulness of PA results in the context of the increasing speculation and uncertainties as time frames on the order of hundreds and thousands of years are considered. The technical and policy considerations for the DOE position and considerations for implementation will be discussed.

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