Evaristo J. Bonano

Consideration of uncertainty in the performance assessment of radioactive waste disposal from an international regulatory perspective

Abstract Regulations governing the disposal of radioactive wastes require that the performance of disposal facilities be assessed quantitatively. Such assessments, commonly called either ‘performance assessments’ or ‘probabilistic risk assessments’, rely on the use of predictive models to arrive at a quantitative estimate of the potential impact of disposal on the environment and on the safety and health of the public. It has been recognized that a suite of uncertainties affect the results of a performance assessment (herein we use ‘performance assessment’ to be synonymous to probabilistic risk assessment). These uncertainties are conventionally categorized as (1) uncertainty in the future state of the disposal system (facility and surrounding medium), (2) uncertainty in models (including conceptual models, mathematical models, and computer codes), and (3) uncertainty in data and parameters. Decisions regarding the safety of a radioactive waste disposal facility must be made in the light of these uncertainties. Neglecting the uncertainties, in either the analysis or the presentation of results, would be a misrepresentation of ones knowledge (e.g. overconfidence) about the performance of the disposal facility. Hence, an approach is needed that would allow the explicit consideration of these uncertainties so that their impact on the estimated consequences of disposal can be evaluated. Regulations for radioactive waste disposal in many countries, explicitly or implicitly, require the consideration of uncertainties in order to arrive at a meaningful decision regarding the safety of a disposal facility. A probabilistic risk assessment approach provides the formalism for treating the uncertainties and the technical basis that the decision makers can use in discharging their duties.

Treatment of uncertainties in the performance assessment of geologic high-level radioactive waste repositories

Federal regulations governing the disposal of high-level radioactive waste in deep, geologic repositories require an assessment of performance over thousands of years. Because of the long regulatory period involved and the complex nature of the events and processes of interest, prediction of the performance of the disposal system will inevitably include uncertainties. These uncertainties come from a variety of sources, and some are quantifiable and others are not. This paper discusses these uncertainties and outlines approaches for their treatment. Recommendations for the potential resolution of current limitations in the treatment of uncertainties in performance assessment are made. Some general issues, as well as a suggested approach for incorporating expert judgment into quantitative performance assessment analysis, are discussed also.

Lessons learned from the Yucca Mountain and WIPP projects.

For more than 30 years Sandia National Laboratories (SNL) has played a key role in the development and implementation of total system analyses of waste management systems in the United States. Two very important applications have been the total system analysis of long term performance that supported (1) the Compliance Certification Application (CCA) for the Waste Isolation Pilot Plant (WIPP) in 1996 and (2) the License Application (LA) for the Yucca Mountain (YM) Repository in 2008.

Insight from Public Surveys Related to Siting of Nuclear Waste Facilities: An Overview of Findings from a 2015 Nationwide Survey of US Residents

The results described in this report are an analysis of nationwide surveys, administered between 2006 and 2015, which measure preferences of US residents concerning the environment and energy sources. The Energy & Environment (EE) survey series is conducted annually by the Center for Energy, Security & Society (CES&S), a joint research collaboration of the University of Oklahoma and Sandia National Laboratories. The annual EE survey series is designed to track evolving public views on nuclear materials management in the US. The 2015 wave of the Energy and Environment survey (EE15) was implemented using a web-based questionnaire, and was completed by 2,021 respondents using an Internet sample that matches the characteristics of the adult US population as estimated in the US Census. A special focus of the EE15 survey is how survey respondents understand and evaluate “consent” in the context of the storage and transportation of spent nuclear fuel (SNF). This report presents an overview of key results from analyses of questions related to consent-based siting and other elements of the nuclear energy fuel cycle.