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:
ationale for determining what part of a volcano’s history is representative of expected future conditions. The evaluation of the uncertainties in the timing and character of past events represents a significant investigation for calculating PE (e.g., Wang and Bebbington, 2012). In many volcanic systems, only a subset of representative deposits has sufficient age information to support the PE calculation. Older deposits might be wholly or partially buried, yet they are still representative of the volcanic system’s past activity and needed for calculation of PE. Because a large range of uncertainties in data and models likely will need to be evaluated for both PE and PH, the NRC staff considers the SSHAC process an acceptable approach to evaluating these uncertainties. The past patterns of eruptions in many volcanic systems vary through time and commonly show patterns of waxing or waning activity (e.g., Yogodzinski et al., 1996). In addition, there might be prolonged periods of inactivity or very low eruption rates, followed by marked changes in activity patterns (e.g., Bebbington, 2007). The tectono-magmatic model should provide a framework to develop an understanding of potential geological controls on eruption patterns and to determine whether such geological processes are expected to occur in the future. Statistical approaches used to evaluate such nonstationary processes require a level of confidence that the model parameters were selected based on traceable interpretations of geological processes and data rather than by mathematical convenience. Typically, PH is evaluated through numerical modeling of individual volcanic phenomena, using a range of characteristics that are interpreted from past volcanic events. A modeling approach is used to account for the incompleteness in the geologic record, which might not accurately represent the range of DG-4028, Page 16 future events. As discussed in IAEA-TECDOC-1795, many different types of numerical models are