EVALUATING RADIOLOGICAL RISKS FROM SEISMOTECTONIC HAZARDS AT THE PROPOSED RADIOACTIVE WASTE REPOSITORY AT YUCCA MOUNTAIN, NEVADA: U.S. NUCLEAR REGULATORY COMMISSION'S RISK-INFORMED AND PERFORMANCE-BASED APPROACH

The U.S. Department of Energy (DOE) plans to apply for a license to construct a repository for high-level radioactive waste that will likely be subjected to seismotectonic hazards including earthquake ground motions, fault displacements, tilting and fracturing. The DOE license application must consider such hazards and demonstrate that, among other considerations, they pose no undue risk to public health and safety for a performance period of 10,000 years. NRC regulations* pertaining to a Yucca Mountain (YM) repository use a risk-informed and performance-based strategy (i.e., they focus on system performance) to adequately protect the public and the environment. DOE must identify features, events, and processes that could affect repository performance (e.g., a seismic hazard scenario might include an earthquake that could cause rockfalls that damage waste containers in drifts and thereby potentially increase dose).

For screening purposes, DOE may estimate the likelihood of such events or groups of events. If the likelihood of the event or scenario is less than 1 in 10,000 per year over 10,000 years, then the event or scenario can be excluded from assessments of performance (10 CFR 63.102(j),114(d)). For the remaining hazards, DOE would need to demonstrate either that: the hazard can be excluded because there is negligible dose contribution; or, its contribution to dose in combination with doses from all other remaining hazards would not exceed the required limit on expected annual dose to an individual. Also, this demonstration of acceptable repository performance must include a systematic evaluation of uncertainty, alternative models (e.g., tectonic), testing of key assumptions, and supporting technical bases for the hazards (e.g., earthquake).

*The regulation (10 CFR Part 63) is available at http://www.nrc.gov/waste/hlw-disposal.html.