Monday, March 31, 2014

Ensuring Seismic Safety at U.S. Reactors

Scott Peterson
The following is a guest post by Scott Peterson, NEI's Senior Vice President of Communications.

Companies that operate America’s nuclear energy facilities today will submit new information regarding seismic safety as part of a series of actions the industry is taking to implement lessons learned from the 2011 Fukushima accident.

This comes at a time of heightened interest in earthquakes given the Los Angeles-area temblors this past weekend. However, the Nuclear Regulatory Commission in 2012 required energy companies to reevaluate potential seismic hazards for each of America’s 100 reactors.

Nuclear energy facilities were designed and built with extra safety margin, in part to be able to withstand an earthquake even beyond the strongest ever at each site. Nonetheless, over the past decades, the industry has re-evaluated the seismic safety of its facilities. Each time new seismic information became available, plant operators have confirmed, and in many cases, enhanced the facility’s seismic protection.

Most recently, the NRC in 2010 concluded that nuclear power plants have significant safety margin to protect against earthquakes, including those with greater ground motion than the earthquakes used to develop the original reactor designs.

The nuclear energy industry, working with the NRC, U.S. Department of Energy and other organizations, developed a new model to characterize the potential for strong earthquakes. The industry is using this model to develop new earthquake hazard estimates for each nuclear plant site. These estimates will be part of a more comprehensive evaluation to ensure nuclear plants continue to be protected against the strongest earthquakes predicted for that site.

There have been only a few cases where powerful temblors exceeded the design parameters for reactors worldwide, and in those cases the plants shut down safely.

The North Anna nuclear power plant in central Virginia is the most recent example. A 5.8 earthquake with an epicenter 11 miles from the facility caused destruction at some local schools and damaged national monuments 80 miles away in Washington, D.C. Yet, there was no damage to North Anna’s safety systems and only minimal chipping and cracking of concrete outside the vital safety areas. That’s due in part to huge shock absorbers and supports that are installed to protect safety systems during forceful quakes.



In the past two years, the industry has developed new assessment processes and an updated ground motion database to undertake the NRC-required update of seismic protection. Using the new ground motion data, the analysis for most U.S. reactors shows a reduced risk to safety from earthquakes, compared to assessments in 1994 and 2008. A few will have a higher risk, but well within a range that will protect the plant and residents near the facility. For those plants, the owners will undertake more sophisticated analyses to determine what additional safety measures should be taken, if any.

All nuclear energy facilities fall within the NRC’s safety range, and the agency’s 2010 determination of safety against potential earthquakes remains valid, NEI Chief Nuclear Officer Tony Pietrangelo wrote in a March 12, 2014 letter to the NRC. “Operating reactors have margin to withstand potential earthquakes exceeding their original design basis,” he wrote.

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