USE OF ONE-ON ANALYSIS TO EVALUATE TOTAL SYSTEM PERFORMANCE

This report presents the results of analyses of the hypothetical performance of the various configurations of selected natural and engineered elements of the proposed Yucca Mountain nuclear-waste repository. These analyses were conducted upon the recommendation of the Nuclear Waste Technical Review Board (NWTRB) regarding an alternative approach to investigate the identified natural and engineered barriers and associated processes with respect to the postclosure performance of the proposed Yucca Mountain repository. The analyses were conducted per Technical Work Plan (TWP) TWP-MGR-PA-000011 REV 00, Section 3.2.4, Task 2, which states that the task involves ''Identification of barriers that are important to repository performance:'' by means of ''one-on'' analyses to gain a better understanding of repository performance relative to previously identified barriers.'' The ''One-on Analysis'' was performed per Administrative Procedure AP-SIII.9Q. The NWTRB previously reviewed similar analyses conducted by Electric Power Research Institute (EPRI) (EPRI 2002 [158069]). The approach of the investigation was to simulate the hypothetical performance of the repository after an arbitrarily chosen successive addition of each of the selected natural and engineered barrier components and associated processes that provide for the overall safety of the repository. Because the repository system will behave as an integrated system, the combined interaction of all the processes and barriers identified in this report will provide the ultimate repository performance as indicated in various performance-assessment analyses for the Civilian Radioactive Waste Management System (CRWMS) M&O 2000 [153246]; Bechtel SAIC Company, LLC (BSC) 2001 [155950]; and Williams 2001 [157307]. The analyses presented in this report should not be construed as an indication, for the chosen additive sequence, of the relative importance on any one barrier or process. Rather, the results of these analyses provide an indication of the relative performance of those barriers and processes and an understanding of their contribution to the overall performance of the proposed repository system. The analyses in this report considered the nominal-performance scenario only, and did not address performance following unlikely disruptive events (e.g., volcanic activity) (10 Code of Federal Regulations (CFR) 63.342)