The major problem with the earthquake-proof designs of current operating reactors is that the basis for their calculations was wrong.
“All of these numbers were derived in the late 60s,” said Lyn Sykes, Higgins Professor Emeritus of Earth and Environmental Science at the Columbia University Lamont-Doherty Earth Observatory in New York. “At that time, they didn’t have recordings of earthquakes from the eastern and central part of the US, so they used western earthquakes as models.
“The difference is that for a given sized earthquake, like the last one at 5.8, earthquakes in the east are felt out to a much larger distance. In California, with softer ground, an earthquake is not felt out to a large distance and damage doesn’t occur out to a large distance. And that does call into question the reliability of their standards.”
Last week’s earthquake, Sykes said, was larger than the design basis for Salem 1&2, Hope and Oyster Creek nuclear plants in New Jersey, and Indian Point 2 & 3 in New York. “For the basis of their designs,” said Sykes, “they used the 1884 earthquake off Sandy Hook near the mouth of New York Harbor, near Coney Island – which gave the quake its name. That quake was about 5.25 in magnitude.”
In that case, he said, the energy associated with last week’s 5.8-magnitude earthquake would be about five times the design basis for these nuclear facilities.
As a percentage of gravitational forces, the design basis used in the construction is 0.15 G for Indian Point; 0.184 for Oyster Creek; and 0.20 for Hope Creek and Salem 1&2. The difference in their design requirements is based on the solidity of the rocks they are built on.
Jon Armbruster a geophysicist at the Earth Institute and co-author with Sykes of an analysis of earthquakes over the last 300 years from Philadelphia to New York, “When they designed these plants, they chose an earthquake and the design basis figure represented how strongly the 1884 quake was felt in the area. There were two other quakes of that magnitude, in 1737 and 1783, and they were felt from Maine to Virginia and caused some chimneys to fall down. The 1884 quake also caused a railway embankment in Peekskill to slump into the river.
In Virginia, the largest earthquake ever recorded was a magnitude 4.8. In the New York City area we have some 300 to 400-year histories and the largest earthquakes known were of a magnitude 5 or 5.3 I don’t think they have been allowing a large enough margin of uncertainty to have planned for a magnitude 5.8.
“What we have learned is that earthquakes around here can occur at a pretty shallow depth. In California, a shallow depth is one or two miles. I’ve been to places around here where earthquakes are not more than 100 meters from the surface. In 1994 there was a magnitude 4.5 earthquake near Redding, Pa., and as closely as we could measure, it was centered 100 yards below the surface. “
When these five regional nuclear power plants were designed, Armbruster added, it was not known that earthquakes could be generated at shallow depths and designers utilized what little data was available from California and other western earthquakes in their planning. “The difference between a California quake and one here was not clearly known back then. Now it is known and quantified that the shaking around here is quite different.
“The nuclear plants in southern New Jersey are not built on actual solid rock, though it is on pretty strong material. To an extent, that reduces the shaking. Each reactor design is different and has its peculiarities of design that need to be individually analyzed in a seismic hazard study.
“It’s like building on Jello. If you put the apartment building on Jello and you shake the bowl, the Jello quivers and the apartment building shakes a lot. To be safe in the earth equivalent of Jello you would have to build your nuclear power plant in what amounts to a concrete boat, so it could essentially float when the Jello shook and be strong enough to remain standing.”
Jim Norville, a spokesman for Dominion, said the company’s engineers and the NRC inspectors are seeking greater understanding of the differences between East and West Coast earthquakes and its implications for the plants critical systems.
We found no significant damage,” he said. But we want a better understanding of why the units shut down.”
So does the NRC. Spokeswoman Diane Screnci said the agency is seeking public comment on a proposed “generic Letter” to plant operators on a review of seismic hazards and design techniques. The response from the North Anna inspection and the generic latter may determine if the NRC mandates retrofitted improvements on existing critical buildings and systems.
Roger Witherspoon writes Energy Matters at www.RogerWitherspoon.com