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:
pacity needed for acceptable performance from potential volcanic hazards. For example, SSCs for air filtration systems typically consider the demands from windblown sands. Volcanic ash falls, however, typically have large amounts of rock particulates, which are significantly smaller than windblown sands and can create larger concentrations of airborne particles. To accommodate the demands from volcanic ash falls, filtration systems would need to consider removal of larger amounts of finer particulates than would occur with windblown sands, which might be present for weeks or longer after an eruption (e.g., Horwell and Baxter, 2006). The Columbia NPP (Energy DG-4028, Page 18 Northwest, and other plants around the world (IAEA-TECCOC-1795) have accommodated such demands by straightforward design and operational changes. The evaluation of volcanic surface-flow phenomena on SSC performance appears more challenging than for ash-fall hazards because of the complex and dynamic processes that occur in surface flows. The demands from a lava flow, for example, might peak several days or possibly weeks after the initial occurrence of a flow at the site. This lag in peak demand might occur because many lava flows tend to stagnate at their flow fronts, while erupted lava continues to infill and thicken the flow (e.g., Hon et al., 1994). Thermal, mechanical, and chemical demands on structures encountered by the lava flow could continue to increase as the flow thickens for many flow scenarios. Consequently, an evaluation of SSC performance during a lava-flow event likely would need to consider the possibility that demands might plateau, and then rapidly increase, for the duration of an eruptive event. If SSC design bases are reevaluated, the NRC staff observes that the volcanic hazards 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