Uncertainties associated with performance assessment of high-level radioactive waste repositories

This report culminates work performed by Sandia National Laboratories (SNL) for the US Nuclear Regulatory Commission (NRC) under FIN A1165 (Technical Assistance for Performance Assessment) on uncertainties associated with performance assessment of HLW repositories. The purpose of this report is to summarize the work in the topical area of uncertainty conducted under FIN A1165. Many different types of uncertainty can affect the performance of an HLW repository. In a performance assessment, these uncertainties should be identified and considered, and to the extent practicable, should be quantified and reduced. Conventionally, the different types of uncertainty are classified in three major categories: uncertainty in the future state of the disposal system; uncertainty in models needed to simulate the behavior of the disposal system; and uncertainty in data, parameters, and coefficients needed for the analysis of the system. All three major categories of uncertainty are covered in this report. Only a short overview is presented with numerous references to SNL reports where different uncertainty topics are discussed in detail; as such, this report is not a stand-alone report. The report can be used by managers to familiarize themselves with the issues regarding uncertainty in HLW repository performance and technical staff as a review of SNL's work for NRC in this area. 52 refs