LESSONS LEARNED FROM APPLICATION OF THE NUREG-2117 GUIDELINES FOR SSHAC LEVEL 3 PROBABILISTIC SEISMIC HAZARD STUDIES FOR NUCLEAR SITES

摘要

In 2012 the US Nuclear Regulatory Commission published guidelines for the implementation of SSHAC Level 3 and 4 hazard assessments that took account of 15 years of experience since the issue of the original SSHAC report in 1997. The guidelines in NUREG-2117 have been implemented in a number of current or recently completed projects. These projects show that the procedures work well in practice and that SSHAC Level 3 projects can be planned in such a way that they can be confidently completed on schedule and within budget. Optimal arrangements in terms of project planning, structure, management, and sequencing of the components of a SSHAC Level 3 study are suggested. One of the key lessons learned is that the Level 3 process has the capacity to be considerably more efficient, but no less effective, than the Level 4 process. Misunderstandings regarding the requirements for, and the value of, Level 1 and 2 studies are dispelled. SSHAC Level 3 processes incorporate significant procedural and technical peer review, thus making them compliant with quality assurance processes for nuclear facilities. There is also a common misconception that intermediate SSHAC Levels exist, whereas there are only the four unique levels and every study can only be classified into one of these categories.