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:
eristics have a transparent technical basis and are accounted for in the model parameters. • Alternative conceptual models have been considered, and the selection of a preferred model (or models) is supported by an appropriate technical basis. • The precision and accuracy of the preferred models have a transparent technical basis, which typically is supported by comparison to empirical observations (e.g., field investigations, natural analogs, laboratory testing). In calculating PH, the tectono-magmatic model should be used to determine whether past patterns of activity provide a sufficient basis to extrapolate to future patterns of activity, or if changes or trends to these past patterns need to be accounted for in extrapolations to future patterns of activity. For example, the volumes of lava flows might show a waning trend with younger eruptions (e.g., Valentine and Perry, 2006). Although a broad range in lava-flow volumes has occurred throughout the eruptive history, the tectono-magmatic model might provide confidence that the system characteristics have shifted to the production of smaller volume eruptions, which better represent the character of potential future eruptions. In this example, the calculation of PH might consider extrapolations based on the smaller volume period of activity rather than the entire history of eruptive activity in the volcanic system. Once either PE or PH has been calculated, the NRC staff considers it acceptable to proceed to Step 5 of the volcanic hazards assessment and determine whether additional analyses are warranted. If the detailed risk insights in Step 5 show that either PE or PH might be significant to facility risk, then the remaining evaluation in Step 4 (i.e., calculation of either PE or PH) should be completed. The NRC 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