Diablo Canyon completes seismic study

11 March 2015

Pacific Gas and Electric (PG&E) says that new and extensive analyses re-confirm that its Diablo Canyon Power Plant can safely withstand extreme natural events, including potential earthquakes, tsunamis and flooding.

The new analyses, known as hazard re-evaluations, will be submitted to the US Nuclear Regulatory Commission this week for independent review.

"Safety is and always will be the top priority for PG&E and Diablo Canyon. That's why seismic, flooding and tsunami safety was at the forefront in the design of the facility. These updated findings are the culmination of years of study and analysis, and further confirm the safety of the plant's design," said Ed Halpin, PG&E's senior vice president and chief nuclear officer.

The hazard re-evaluations used the latest regulatory guidance, scientific methods and models, site-specific information and independent expertise to re-evaluate the impacts that earthquakes, large waves and flooding could have on the Diablo Canyon facility.

The updated seismic assessment represents "a more extensive evaluation of the seismic hazard than previously performed," PG&E says. Prior evaluations determined the ground shaking from an earthquake on a particular fault in the region, based on historical records and geological evidence, and then compared this information against structures, systems and components at the facility to ensure they could withstand seismic ground shaking.

Using the NRC's Senior Seismic Hazard Analysis Committee (SSHAC) process, independent seismic experts publically re-evaluated existing and new seismic information, including data acquired during the advanced seismic studies recently performed near Diablo Canyon, to re-evaluate how earthquakes could potentially impact the facility.

"The updated seismic source model for Diablo Canyon incorporates an extensive body of new onshore and offshore data and emerging new scientific concepts to characterize earthquake sources," said Bill Lettis, who serves as one the key technical leads for the SSHAC process."For example, it is the first earthquake model developed for a nuclear site that allows for multi-fault linked ruptures to produce large maximum earthquakes."

PG&E's flooding and tsunami hazard update also involved the use of the latest NRC guidance to determine the maximum potential waves and rainfall that could impact Diablo Canyon.

The study determined that the plant's key safety systems and components continue to be safe from tsunamis, including those generated from underwater landslides and earthquakes. The plant's design is also deemed appropriate to withstand expected storm flooding.

Photo: Diablo Canyon nuclear plant

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