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:
site selection stage. • Debris Flows: Volcanic debris flows typically occur when a mass of pyroclastic material, either during or after an eruption, becomes mixed with water and flows down gradient. As the flow travels down gradient, it incorporates additional sediment and water and typically overtops existing stream or river channels. Volcanic debris flows typically contain greater than 50 percent suspended solids (which can include automobile-sized boulders) within tens of kilometers of the source, but they eventually dilute to more typical flood conditions as distance further increases from the source. Volcanic debris flow can occur with little warning time and can be triggered by DG-4028, Page 6 either slope failure or intense rainfall events. IAEA SSG-21 concluded that debris flows at a proposed site represented an exclusion condition at the site selection stage. • Volcanic Earthquakes: The rise of molten rock from deep in the earth’s crust typically creates swarms of small-magnitude (i.e., generally less than M5 on the moment magnitude scale) earthquakes within tens of kilometers of the eventual surface eruption. Volcanic systems in the United States are located in active tectonic terranes, which typically have the potential to produce significantly larger magnitude earthquakes from local or regional tectonic sources. IAEA SSG-21 recommends consideration of a site-specific volcano-seismic hazard assessment for a site affected by other volcanic hazards. • Other Proximal Hazards: Some additional volcanic hazards can occur within several tens of kilometers of a volcano or new volcanic vent. Depending on the characteristics of the volcanic systems in the site region, some consideration might be warranted for (1) potential debris avalanches arising from slope failures, (2) tsunami or seiche phenomena if a large debris avalanche enters a large body of water, and (3) the possibility of hydrothermal systems or emission of volcanic gases reaching a proposed