NRC: Despite fault, quake risk not a factor in Limerick relicensing

LIMERICK — Deep in the ground, beneath the poured concrete and reinforced steel of the Limerick nuclear plant’s evaporation towers, lie several sleeping subterranean threats.

The plant’s operators and the regulators of the federal agency that oversees nuclear plants say these threats are likely to stay asleep. 

And even if the Sanatoga fault, the Chalfont fault or the Ramapo fault awoke and shook those landmark towers in an earthquake, it’s unlikely that quake would be severe enough to cause enough damage to the plant to create a disaster.

 That was the conclusion reached by geologists who mapped the local faults in 1974 for Philadelphia Electric Company.Despite improvements in geologists’ understanding of the East Coast earthquake picture — clearly punctuated by last August’s unexpected Virginia tremor felt in several states — that conclusion remains unshaken for both the plant’s current owner, Exelon Nuclear, and the Nuclear Regulatory Commission that oversees the plant.

Further, although newly revised earthquake risk assessments will be a factor in any new nuclear plants licensed by the NRC, they will not be considered when evaluating the 20-year license renewal for Exelon Nuclear’s Limerick Generating Station or any other nuclear plant for that matter.

In the end, it comes down to how risk is calculated.

“It is concluded that movement along the shears could not have occurred later than 500,000 years ago,” reads a July 30, 1974, letter signed by Joseph A. Fischer, a partner at Dames and Moore, and Bernard Archer, a senior geologist for the firm.

“In all probability” the faults have been inactive since 150 million to 200 million years ago, according to the letter that accompanied the green-shaded map showing the Sanatoga fault and Linfield fault zone close to a nuclear power plant.But three independent earthquake experts said recently that they agreed with the Dames and Moore assessment of the earthquake risk being low, but they also all agreed that the operative word here is “probability.”

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