[en] Total System Performance Assessment (TSPA) is the use of numerical models representing natural processes to evaluate the future performance of natural and engineered components of the repository system. Future performance, in this context, means performance after the operational period and the emplacement of final seals. The basis for developing a TSPA is data collected during surface-based, underground, and laboratory tests and studies; measurements and interpretations by scientific experts; selected information from documented studies; and information related to the engineered barriers and the repository design. The numerical models are developed based on the laws and principles of chemistry and physics, where possible, augmented by empirical studies where necessary, and represent processes relevant to the system using data from field investigations and laboratory studies. The TSPA is a key component of the License Application being submitted by the US Department of Energy (DOE) to the US Nuclear Regulatory Commission (NRC). The NRC must be able to find, on the basis of DOE's demonstration, that there is reasonable expectation that nuclear waste can be disposed of safely for many thousands of years without posing an unacceptable risk to public health and safety. TSPA results include an evaluation of uncertainties inherent in assessing long-term repository performance. Uncertainties are introduced by spatial and temporal variability in current and future site conditions, and the complexity of the coupled physical and chemical processes operating in a repository over time. Results from computational models are not a precise prediction of the actual performance of a repository. However, although significant uncertainties exist, there will be confidence in the safety of the system if there is a comfortable margin between pessimistically predicted results and the regulatory definitions of safety, plus additional evidence, e.g., natural or other analogues supporting the credibility of the analyses

[en] With the implementation of nuclear power as a major energy source, the United States is increasingly faced with the challenges of safely managing its inventory of spent nuclear materials. In 2002, with 438 nuclear power facilities generating electrical energy in 31 nations around the world, the management of radioactive material including spent nuclear fuel and high-level radioactive waste, is an international concern. Most of the world's nuclear nations maintain radioactive waste management programs and have generally accepted deep geologic repositories as the long-term solution for disposal of spent nuclear fuel and high-level radioactive waste. Similarly, the United States is evaluating the feasibility of deep geologic disposal at Yucca Mountain, Nevada. This project is directed by the U.S. Department of Energy's Office of Civilian Radioactive Waste Management (OCRWM), which has responsibility for managing the disposition of spent nuclear fuel produced by commercial nuclear power facilities along with U.S. government-owned spent nuclear fuel and high-level radioactive waste. Much of the world class science conducted through the OCRWM program was enhanced through collaboration with other nations and international organizations focused on resolving issues associated with the disposition of spent nuclear fuel and high-level radioactive waste

[en] A key component of the US energy program is to provide for the safe and permanent isolation of spent nuclear fuel and long-lived radioactive waste produced through programs related to national defense and the generation of electric power by nuclear utilities. To meet this challenge, the US Department of Energy (DOE) has developed a multi-faceted approach to the geologic disposal of long-lived nuclear wastes. Two sites are being developed or studied as current or potential deep geologic repositories for long lived radioactive wastes, the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico and Yucca Mountain, Nevada