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
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CFR Title: 

Content:
mbia Generating Station (Columbia) in Washington is the only operating NPP in the United States with a design basis for structures, systems, and components (SSC) that considers demands from a volcanic hazard. The Columbia site is approximately 215 kilometers (km) (135 miles (mi)) east of Mount St. Helens, which had its last major eruption in 1980. Because of its proximity to Cascade volcanoes, the Columbia NPP includes volcanic ash fall as a design- and operational-basis event (e.g., NRC, 2014b). The Columbia safety case includes demonstration of the plant’s ability to withstand the wet and dry loads of potential ash-fall deposits, operational considerations for mitigating the effects of ash falls on plant SSCs, and the installation of oil-bath air filters during an ash-fall event. The Trojan Nuclear Power Plant in Oregon was located approximately 55 km (34 mi) southwest of Mount St. Helens, along the western bank of the Columbia River. Because of its proximity to Mount St. Helens and other Cascade volcanoes, plant licensing considered the potential effects of future volcanic eruptions (PGE, 1976). The potential effects of future volcanic hazards were considered to have an insignificant effect on the design and operation of the plant because of the low frequency of occurrence and the characteristics of potential volcanic phenomena expected at the site (e.g., Oregon Department of Geology and Mineral Industries, 1978). Subsequently, the May 1980 eruption of Mount St. Helens created debris flows that partially infilled the Columbia River channel below the Trojan water intake structures and deposited several millimeters of ash fall at the site (Schuster, 1981). Volcanic hazards at Trojan were reevaluated based on the 1980 eruption characteristics (PGE, 1980, as referenced in Schuster 1981), and no changes were made to the plant’s operating basis. Trojan was decommissioned in 1992. The NRC also licensed two ISFSIs on or adjacent to the Idaho National Laboratory: