Applications of performance assessment in support of the Exploratory Studies Facility (ESF) design

Performance assessments (PA) are an integral part of the exploratory studies facility (ESF) design effort currently underway as part of the Yucca Mountain Site Characterization Program. These assessments are part of an interdisciplinary effort that requires input from ESF design, construction, operation, and testing as well as from performance assessment personnel to make judgments about the effects of ESF construction, operation, and testing on the ability of the repository to isolate waste and on tests conducted in the ESF. These judgments lead to the formulation of controls or limitations that when imposed will provide reasonable assurance that the ESF will not degrade the ability of the site to isolate high-level radioactive waste or interfere with tests. PA draws from a knowledge base, which includes interpretations of the results of specific analyses in the areas of fluid flow, geochemistry and materials, thermal mechanical, and total systems. The process for applying performance assessments to support the design and construction of the ESF is outlined. In addition, the role of performance assessment is illustrated by describing two controls on the use of water at Yucca Mountain and the two PA analyses on which these controls are based.