The Department of Energy is taking a new look at earthquake hazard at Hanford, conducting an assessment that will update the last comprehensive one conducted in 1996.
Federal regulations require assessments for natural hazards, such as earthquakes, at sites such as the Hanford nuclear reservation to be updated when there are significant changes in methods or data.
That now appears to be the case.
The U.S. Geological Survey has shown that the active faults of the Puget Sound Region are connected to ridges in the Mid-Columbia by faults that cross the Cascades, according to Steve Reidel, the Herald's Northwest Geology columnist.
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Previously, geologists looked at Eastern Washington as a geological world independent of the Puget Sound, Reidel said.
In addition, the USGS has dug trenches down to fault lines near Selah and Ellensburg that showed the faults there cannot be considered inactive, said Bob Bryce of Pacific Northwest National Laboratory. The DOE national lab in Richland has a contract to perform the new analysis, which will include outside experts, and will be managed by Bryce.
Other agencies, including British Columbia and Washington utilities, also are producing information that could contribute to a new analysis of the earthquake hazard at Hanford. And more seismic monitoring has been done at Hanford since that 1996 analysis.
In the region, the largest earthquake recorded was a magnitude-5.7 earthquake 72 miles from Hanford at Milton-Freewater in 1936, according to data collected for the design of the Hanford vitrification plant. In addition, Eastern Washington was hit by an earthquake with an estimated magnitude of 7.3 in 1872 near Lake Chelan, Reidel said.
Methods also have changed since the last full assessment in 1996. The state of the art of probabilistic analysis has improved, said Paul Harrington, DOE assistant manager of technical and regulatory support. The Nuclear Regulatory Commission has recently improved its guidance for probabilistic analysis, which includes the process of gathering data, evaluating it and using it in a hazard model.
The process will estimate hazards based in part on the characterization of information such as where and how often earthquakes occur in about a 50-mile radius from Hanford and how big they are.
Information about how ground motion is transmitted to Hanford as it moves through rock also will be considered. Factors such as a possible quake's magnitude, distance from Hanford and faulting direction will be considered in the ground motion characterization.
Then a more specific characterization will be done to look at the different rock formations and other geology at the Hanford. Because of work in 2006 and 2007, including drilling bore holes, to determine if seismic design standards were adequate for the Hanford vitrification plant, little additional work may need to be done on site geology.
A project kickoff meeting is planned next week in Richland. Then three workshops will be held to identify technical issues and data needs, to discuss alternative interpretations of the data and then to allow technical teams to receive feedback from a peer review panel.
A report on the study is expected to be completed in August 2014.
Until it is completed, DOE won't know whether there is a need to update seismic design standards for new facilities at Hanford or a need to take a look at existing facilities, Harrington said.