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Adding a Piece to the Seismic Puzzle

Clifford Munson
Sr. Technical Advisor for Nuclear Plant Siting
Office of New Reactors

One of the important lessons from 2011’s Fukushima Dai-ichi accident was the need for U.S. reactors to better understand their earthquake hazard. Reaching that understanding is a bit like assembling a jigsaw puzzle, and reactor owners in the central and eastern parts of the country are sending the NRC one of their pieces this month.

seismicThe graphic shows the three pieces of information U.S. reactor owners need in order to analyze their specific hazard:

• Where quakes are generated

• How the country’s overall geology transmits quake energy, and

• How an individual site’s geology can affect quake energy before it hits the reactor.

The first two pieces are taken care of. The NRC partnered with the Department of Energy and the Electric Power Research Institute to publish updated earthquake source information last year. We also recently approved the most recent model of quake energy transmission.

U.S. plants east of the Rocky Mountains have been enhancing their ability to describe their sites’ soil and rock properties, in some cases obtaining more information on what lies beneath the reactors. Sites made up primarily of hard rock (at left in the graphic) tend to amplify high-frequency quake energy, while sites with more of a soil-like makeup (at right) tend to amplify low-frequency energy.

Central and eastern U.S. reactor owners are starting the process of putting all three pieces together to update their site’s hazard. They’ll report the results to the NRC by March of next year. They’ve provided updates on their sites’ soil/rock makeup now so the NRC can examine the information and ensure it meets the basic standards needed for the overall hazard review. Plants west of the Rockies have a more complicated version of the puzzle to consider, so they’ll submit information to the NRC later.

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