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:
staff also notes that an acceptable volcanic hazards assessment can skip an intermediate evaluation of risk insights (i.e., using only PE or PH), proceed to calculate both PE and PH, and then evaluate the detailed risk insights. DG-4028, Page 17 Step 5: Develop Detailed Risk Insights Using the same approach as in Step 3, risk insights can be developed using a simplified analysis that assumes the occurrence of either a volcanic eruption (i.e., PE) or a volcanic hazard (i.e., PH) would represent a beyond-design-basis event. In this simplified approach, the analysis could assume that the probability of SSC failure (i.e., unacceptable performance) is represented in the PRA by either the PE or PH. Using these assumptions, the PRA results could be evaluated to determine whether the total system performance would be acceptable for a volcanically induced failure of the SSCs. This evaluation would necessarily include the suite of considerations used to make risk-informed regulatory decisions (e.g., SECY-98-144). If these risk insights determine that volcanically induced failure of SSCs result in acceptable performance of either PE or PH, then no further volcanic hazards assessment is warranted. If performance is unacceptable, or other risk insights warrant consideration, then the analyst returns to Step 4 and evaluates the unanalyzed component of the volcanic hazard (i.e., either PE or PH). Once both PE and PH are evaluated, a simplified PRA can be conducted using the assumption that the probability of SSC failure (i.e., unacceptable performance) is represented in the PRA by (PE x PH). Using this assumption, the PRA results could be evaluated to determine whether the total system performance would be acceptable for a volcanically induced failure of the SSCs. This evaluation would necessarily include the suite of considerations used to make risk-informed regulatory decisions (e.g., SECY-98-144, NRC 2019b, and RG 1.174). If these risk insights determine that volcanically