Preliminary preclosure safety analysis for a prospective Yucca mountain repository

A quantitative probabilistic safety assessment was performed for the reference conceptual repository design being used as the basis for the development of the Yucca Mountain Site Characterization Plan. A new methodology to quantify radioactive source terms for the air pathways was also developed and applied in the assessment. The assessment identified 21 potential initiating internal and external events applicable to the prospective site for which 149 potential accident scenarios were defined with event tree analysis. Of these accident scenarios, 13 occurred with probabilities ranging between 10/sup -6/ to 10/sup -9/ per year and with estimated offsite 50-year dose commitment consequences ranging from 110 to 1,100 mrem, respectively. These 13 reference accident scenarios represent the most severe consequences identified that the operation of a repository could initiate. The remaining scenarios had either probabilities of occurrence of less than 5 x 10/sup -9/ per year or offsite dose consequences of less than 50 mrem