The Nuclear Regulatory Commission, following up on work underway when the Fukushima accident highlighted the importance of seismic issues in the nuclear arena, has set a priority list for 21 of 59 nuclear power plant sites in the central and eastern United States to conduct in-depth analyses of the plants’ updated earthquake risk.

A detailed risk analysis is due by 30 June 2017 from these plants:

Callaway – Fulton, Mo.
Cook – Bridgman, Mich.
Indian Point – Buchanan, N.Y
North Anna – Louisa, Va.
Oconee – Seneca, S.C.
Peach Bottom – Delta, Pa.
Pilgrim – Plymouth, Mass.
Robinson – Hartsville, S.C.
Vogtle – Waynesboro, Ga.
Watts Bar – Spring City, Tenn.

A detailed risk analysis is due by 31 December 2019 from these plants:

Beaver Valley – Shippingport, Pa.
Browns Ferry – Athens, Ala.
Catawba – York, S.C.
Dresden – Morris, Ill.
Fermi – Newport, Mich.
Hatch – Baxley, Ga.
LaSalle – Marseilles, Ill.
Oyster Creek – Forked River, N.J.
Palisades – Covert, Mich.
Summer – Jenkinsville, S.C.
Sequoyah – Soddy-Daisy, Tenn.

Also, these 21 plants, and another 23 sites whose requirements for a detailed risk evaluation remain undecided, have until December 2014 to complete an "expedited approach" review to evaluate and reinforce key core cooling equipment to ensure plants could safely shutdown if an earthquake in fact were to occur at the higher seismic ground motion. If these reviews show the need to enhance that equipment, the work must be complete by December 2016, the NRC said.

The list came from the NRC’s work reviewing and updating earthquake hazard information for the 59 operating reactor sites and one unfinished reactor site east of the Rocky Mountains, it said. The sites submitted this information in March as part of the NRC’s implementation of lessons learned from the 2011 Fukushima nuclear accident. The submittals showed the plants, which have substantial safety margin above their designs’ anticipated hazards, are safe for continued operation while more work is done. Should this additional analysis indicate more immediate actions are necessary, the NRC will ensure the plants respond appropriately.

"Since the availability of NRC’s technical expertise is limited, the NRC decided to prioritize the follow-on work."

Since the availability of NRC’s technical expertise is limited, the NRC decided to prioritize the follow-on work. The priority list is based on several factors that deal with how a site’s quake hazard transmits energy at frequencies that can affect a plant’s structures, pipes, pumps and related safety systems. A large change between a plant’s original and new hazards at those frequencies was a key consideration in determining a plant’s priority. Strong overall ground motions at those frequencies also influenced a plant’s priority, as can information from earlier risk evaluations, NRC said.

If the NRC eventually concludes that any of the 23 sites whose requirements for a detailed risk evaluation currently remain undecided does in fact need that review, it would be due by 31 December 2020.

The Columbia (Benton County, Wash.), Diablo Canyon (Avila Beach, Calif.) and Palo Verde (Wintersburg, Ariz.) sites must submit their new hazard estimates in March 2015. The NRC will use the same process to determine which of these sites require additional risk analysis, NRC said.

The NRC has concluded that 17 plants do not need to carry out a seismic hazard risk analysis, because they were able to demonstrate that their original design covers the new risk.They are: Braidwood; Byron; Comanche Peak; Farley; Ginna; Grand Gulf; Harris; Hope Creek; Millstone; Nine Mile Point; Prairie Island; River Bend; St Lucie; South Texas Project; Susquehanna; Turkey Point; Waterford.

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