The Electric Power Research Institute (EPRI) has conducted independent total system performance assessments (TSPAs) of the proposed Yucca Mountain spent fuel and high-level radioactive waste repository for 15 years. EPRI uses its TSPA code, IMARC, currently in its eighth version. The major results of the IMARC-8 analyses are presented in this paper. In all of the situations evaluated by EPRI using IMARC-8, the results for the reference repository concept for Yucca Mountain are well within the regulatory criteria established in the applicable regulations, 10 CFR 63 and 40 CFR 197. Further analyses indicate that at least two of the repository barriers must fail to function as anticipated for dose risks to rise as much as one millirem per year (1/15th of the regulatory limit).