Hazard Analysis Results Help Assure Seismic Safety of Facility Designs at Hanford
Plate Tectonic Setting of the Hanford Site (Hanford PSHA 2014). Earthquake hazard depends on the magnitudes and locations of likely earthquakes, how often they occur, and the properties of the rocks and sediments that earthquake waves travel through.
Publication of the Hanford Sitewide Probabilistic Seismic Hazard Analysis (PSHA) in November 2014 represented the first step in a process to reassess the seismic safety of facilities on the Hanford Site and to establish design requirements for new facilities. The document is the culmination of a three-year study conducted to characterize the vibratory ground motion hazard from potential future earthquakes at Hanford Site.
The PSHA team developed new seismic source characterization and ground motion characterization models to serve as the basis for new seismic hazard curves for the Hanford Site. Hazard curves are used to determine the probability of the occurrence of ground motions relative to the ability of designed structures to withstand them. The PSHA results must be combined with information about the shallow basalts and sediments at each specific facility of interest and with information about the design of the facility to determine its safety. Follow-on design safety-determination efforts are being planned for some U.S. Department of Energy (DOE) facilities and the Columbia Generating Station operated by Energy Northwest.
Waste Treatment Plant Seismic Hazard Analysis
Using the PSHA results, DOE is in the process of completing formal calculations of anticipated ground motions at the Waste Treatment Plant (WTP) site and comparing those ground motions with the design bases for the facility. (Preliminary calculations for the WTP based on site geology data and plant design information indicated that for the most part, predicted ground motions will be similar to or lower than estimates used as the basis for the WTP design.)
Sponsored by DOE and Energy Northwest, the PNNL-led collaborative analysis fulfilled requirements for (1) DOE to update a decade-old Hanford-wide seismic hazard analysis, and (2) Energy Northwest to conduct a PSHA using Senior Seismic Hazard Analysis Committee Level 3 procedures for the Columbia Generating Station. The latter was done in response to a request from the U.S. Nuclear Regulatory Commission that all nuclear power plant licensees in the United States update their seismic hazard analyses and review the seismic safety of their power plants (in the aftermath of the accident at the Fukushima nuclear power plant in Japan).
The PSHA was conducted for several reasons:
- guidance for how seismic studies are to be performed has changed significantly since the last Hanford sitewide PSHA conducted in 1996,
- new information has been developed about seismicity in the Pacific Northwest, and
- new approaches have been developed for estimating ground motion resulting from earthquakes.