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:
rences 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 clear indicators of an impending eruption in the months or weeks before an actual eruption. Patterns of precursory earthquake activity might be very similar to movement of other fluids at depth, or of some tectonic earthquakes (e.g., McNutt, 1996). Volcanic systems also can produce monitoring signals, such as elevated earthquake activity or degassing events, which suggest a high likelihood of a near-term eruption, only to have those signals abruptly cease and the volcanic system return to ambient conditions (e.g., Hill et al., 1991). To accommodate these uncertainties, an acceptable operational plan for mitigation of potential volcanic hazards needs to provide confidence of the following: • Appropriate monitoring resources are established to provide early indication of a potential eruption. DG-4028, Page 19 • Changes in monitored activity relate to clear criteria for proposed mitigative actions. • Sufficient time is available between the start of volcanic unrest, implementation of proposed mitigative approaches, and arrival of potential volcanic hazards at the site. The proposed mitigative actions must be practicable in the timeframe between the initial indications of a potential eruption and the likely arrival time of volcanic hazards at the site. Although this timeframe will be highly dependent on specific conditions at individual volcanoes, this timeframe typically can be on the order of days to weeks. The Columbia plant has developed practicable mitigative actions for volcanic ash falls. These actions include removal of ash-fall deposits from vulnerable structures; installation of oil-bath or enhanced air filters on diesel generators; and adjusting heating, ventilation, and air conditioning equipment. The actions would allow the Columbia plant to safely shut