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:
ent forms, although some new vents have formed within a day of earthquakes being felt in the vent area. IAEA SSG-21 concluded that the opening of a new volcanic vent within approximately 1 km (0.6 mi) of a proposed site represented an exclusion condition at the site selection stage. • Lava Flows: Lavas are dense (roughly 2,500 kg/m3, 156 pounds per ft3), hot flows (1,000–1,200 degrees C, 1,830–2,200 degrees F) of molten rock that tend to follow topographic gradients but often overcome topographic obstacles. Lava flows generally travel 1–10 meters per second (2–22 miles per hour), but greater or lesser speeds can occur based on site conditions. Flows generally extend up to tens of kilometers from a vent and often spread laterally from a central channel. In some terrains, lava flows can block drainages and create water impoundments and upstream flooding. IAEA SSG-21 concluded that lava flows at a proposed site represented an exclusion condition at the site selection stage. • Pyroclastic Density Currents: Pyroclastic density currents are moving mixtures of pulverized rock and hot volcanic gases (greater than 300 degrees C [570 degrees F]) that can flow across the ground at speeds of hundreds of meters per second. Some volcanoes in the United States (e.g., Mount St. Helens) have the potential to produce small-volume pyroclastic density currents, which usually travel less than tens of kilometers from the vent. A few volcanoes in the United States (e.g., the Yellowstone Caldera) have produced large-volume pyroclastic density currents, which have traveled hundreds of kilometers from the vent and are capable of overtopping large topographic features. IAEA SSG-21 concluded that pyroclastic density currents at a proposed site represented an exclusion condition at the 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.