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:
rds assessment should reevaluate the risk insights obtained in Step 5, using the appropriate values for SSC performance with the anticipated demands of a volcanic event. The likelihood of the volcanic event should reflect (PE x PH) at an appropriate likelihood of the specific demand being exceeded during the volcanic event. If the reevaluated risk insights are acceptable for SSC performance during a volcanic event, then no further volcanic hazards assessment is warranted. If additional capacity or margin in the system is required, the volcanic hazards assessment should consider the evaluation of mitigating strategies in Step 7. Step 7: Evaluate Mitigating Actions If the preceding steps of the volcanic hazards assessment indicate that volcanic hazards have the potential to affect the design and operation of the proposed new reactor, the analysis can evaluate the potential for human actions to mitigate the effects of the volcanic hazards. These actions typically involve the development of operational procedures for timely responses to a future volcanic event. Responses could range from enhanced maintenance procedures (e.g., removal of volcanic ash-fall deposits from electrical insulators; Wilson et al., 2012) to construction of diversionary structures against surface flows. A key challenge in using mitigation actions for volcanic hazards is developing a robust technical basis for the amount of time that might be available between the onset of volcanic eruptive activity and the arrival of hazardous phenomena at the site. Although some historical volcanic eruptions have occurred in well-monitored locations, there are considerable uncertainties in applying these eruptive patterns to different volcanic systems. These uncertainties arise from the potentially significant differences in local-scale (and regional-scale) tectono-magmatic processes that control the ascent and eruption of molten rock from deep in the earth’s crust. In addition, volcanic systems rarely provide