On November 2, 2001, the U.S. Nuclear Regulatory Commission (NRC) issued its final regulations for a potential geologic repository at Yucca Mountain. The NRC regulations establish criteria to evaluate the safety of a potential repository that the U.S. Department of Energy (DOE) plans to build, operate, and close at Yucca Mountain. Estimation of long-term behavior of the repository will be uncertain because of the first-of-a-kind nature of a geologic repository at Yucca Mountain, the inherent complexity and variability of any geologic formation, and the long regulatory period. Confidence in the long-term safety of the repository is supported by criteria that call for: a comprehensive evaluation of overall repository performance, the repository to be comprised of multiple barriers (both natural and engineered), and testing to confirm the performance of the repository and its barriers.

A comprehensive evaluation of performance requires identification of the features, events and processes (FEPs) that could affect repository performance; consideration of the uncertainty in parameters and models used to represent the FEPs; and evaluation of the complex interactions between the engineered barriers and the geology, hydrology and chemistry of the natural system. The understanding of repository performance, including consideration of uncertainties, must be supported by a wide variety of data and testing; such as information obtained from laboratory tests, field investigations, and natural analog studies. If NRC grants a license to DOE, the regulations require DOE to continue testing and evaluation of the adequacy of the assumptions, data, and analyses that permitted the construction of the repository and subsequent emplacement of waste. This required "performance confirmation" program would include in situ monitoring, and laboratory and field testing. Thus, NRC's licensing decision will be based on a comprehensive understanding of the overall behavior of the repository and its barriers that is supported by scientific information and data, and confirmed by an ongoing monitoring and evaluation process.