Document: NRC Regulatory Guide
Document ID: 46b2c829-ce4c-4a6a-8a01-908725558ffe
Document Type: regulatory_guide
Title: Volcanic Hazards Assessment for Proposed Nuclear Power Reactor Sites + HISTORY - HISTORY 03/2020 – DG-4028-Proposed New Guide
Source: NRC Regulatory Guide Division 4
Source URL: https://www.nrc.gov/docs/ML2000/ML20007D621.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-4.26
CFR Part: 
CFR Title: 

Content:
a valuable mechanism to assess whether potential volcanic hazards are significant to safety. The approach to developing these insights relies on having an appropriate PRA for the proposed facility and using the intermediate results from the volcanic hazards assessment to test the sensitivity of key PRA assumptions. In practice, sensitivity analyses would assume that the performance of SSCs are degraded because of the conditional likelihoods of volcanic hazards occurring and then would assess the significance of that assumption to the PRA results. The significance of the volcanic hazards assessment could then be determined using the suite of information available to support risk-informed decision-making (i.e., items a–e in SECY-98-144). Senior Seismic Hazards Analysis Committee Study Guidelines The scientific community has not achieved consensus on specific modeling approaches that are both generally acceptable and suitable for evaluating low-likelihood volcanic phenomena at facilities that have stringent safety requirements. Selection of an appropriate approach is important because alternative modeling approaches can result in significantly different volcanic hazards assessment results. A volcanic hazards assessment must rely on interpreting the characteristics of poorly preserved past events and projecting these events into a range of potential future events. These projections must consider the possibility that new phenomena or patterns that are inconsistent with the patterns of past activity might occur in the future. Potentially significant uncertainties in data and models usually are evaluated and propagated through a probabilistic assessment. A well-documented probabilistic assessment provides an acceptable basis for NRC regulatory review and safety decisions (e.g., Volume 60 of the Federal Register, page 42622 [60 FR 42622]). The NRC established the use of the Senior Seismic Hazards Analysis Committee (SSHAC) process as an acceptable method to account for a