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:
Hazard Potential A traditional volcanic hazards assessment would first calculate the probability of a future volcanic eruption occurring (PE), then calculate the conditional likelihoods of potentially hazardous phenomena reaching the site (PH). The product of these two probability distributions would then be convolved to produce a probability of occurrence (or exceedance) for volcanic hazards at a site. The NRC staff believes that this traditional approach represents one acceptable method for conducting a volcanic hazards assessment. Nevertheless, the NRC staff notes that efficiencies can be gained in some volcanic hazards assessments by initially evaluating either PE or PH independently, then developing risk insights to determine if additional volcanic hazards analyses are warranted. If either PE or PH indicates a potential for significant effects on facility safety (i.e., Step 5 in Figure 1), then analysis of the complementary DG-4028, Page 15 probability (i.e., either PE or PH) would be needed. However, if either PE or PH shows that potential volcanic hazards did not significantly affect safety, then additional analyses would not be warranted. This stepwise approach to conducting volcanic hazards assessments allows applicants to avoid unnecessary investigations unless initial probability estimates indicate potential safety significance for volcanic hazards. Many volcanic systems can have relatively large uncertainties in the timing of past events, which can be challenging to evaluate. Nevertheless, PE calculations will depend on interpretations of these timing uncertainties. In contrast, the range of past hazard characteristics might represent more straightforward interpretations of the geologic record, which could be used to evaluate PH with greater confidence and efficiency than PE. In such situations, initially evaluating the risk significance of either PE or PH provides a risk-informed basis to decide whether additional analyses are warranted. In addition,