Demonstration of a decision analysis methodology for assessing the performance of the Yucca Mountain site in Southern Nevada

This study develops a methodology for making decisions involving complex earth science systems and demonstrates its feasibility in relation to issues of radioactive waste storage at Yucca Mountain, Nevada. The basic approach involves a team of experts working together to identify and evaluate the key events, processes and parameters that are critical to the decision process. This basic information and calculational models required to represent various phenomena are integrated in a logic tree. The logic tree for the Yucca Mountain analysis is composed of 11 nodes that represent climatic, volcanic and tectonic events, various chemical and mass transport processes, and engineering factors that bear on the performance of the repository. These inputs are integrated into a software package to make calculations of expected releases of radioactivity as a function of time at the accessible environment. The demonstration application identified infiltration, container design and waste leaching rates, and various mass transport parameters as key factors that critically affect releases. At this stage, the most important outcome of the modeling effort is the demonstration that this approach to decision analysis of a radioactive waste repository is feasible with current knowledge and technology. Further, it shows that rational and defensible decisions can be made regarding the acceptability of a site even in the face of recognized uncertainties.