DEVELOPMENT OF VOLCANIC HAZARD ANALYSIS METHODOLOGIES FOR YUCCA MOUNTAIN, NEVADA

Geologic studies related to volcanism and volcanic hazard at Yucca Mountain were conducted during the period two decades prior to the first formal probabilistic volcanic hazard analysis (PVHA) carried out in 1996. The PVHA was the first “expert elicitation” conducted for the project and one of the first applications of the expert judgment methodology in NUREG/CR-6372 (the “SSHAC” methodology) proposed by the NRC, DOE, and electric utilities. Since that time, the SSHAC process has been used for nuclear facilities throughout the US and in several other countries. Steps in a SSHAC process include: development of a comprehensive database, establishment of specific roles for the experts and all participants, conduct of multiple interactive and facilitated workshops to identify issues and to promote debate among technical proponents, feedback to the experts to identify issues of most hazard significance, complete documentation, and participatory peer review of all activities. Information from the PVHA was used to focus geologic field studies and geophysical investigations in the ten years following. In preparation for licensing, the PVHA-Update was conducted in 2008, which was a completely new SSHAC Level 4 assessment based on new data, models, and methods. The study incorporated new spatial and temporal models for volcanic hazard and dealt with forward time periods up to 1 My. High-resolution aeromagnetic data, drilling, and geochemical analyses were conducted to support the assessment. The PVHA-U is considered the standard for volcanic hazard analyses and for the implementation of the SSHAC assessment methodology.