Margin of Error

The Trojan Nuclear Plant on the Banks of the Columbia River Is Under Construction by Portland General Electric Environmentalists Strongly Oppose the Project 05/1973
Trojan Nuclear Plant from the U.S. National Archives

The New York Times article “Nuclear Agency Tells a Concerned Congress That U.S. Industry Remains Safe” had a curious statement from Gregory Jaczko, of the chair of the Nuclear Regulatory Commission, in front of Congress.

“U.S. nuclear facilities remain safe,” Mr. Jaczko told two House Energy and Commerce subcommittees, which had originally planned to consider his agency’s budget for the coming fiscal year at the hearing. “We will continue to work to maintain that level of protection.” Reactors are designed to meet the challenges of “the most severe natural phenomena historically reported,” he said. For earthquakes, that means any that occur within 200 miles of the reactor, and a margin of error, he said.

Jaczko sounds similar to the planning the Japanese did. Earlier I read a Wired Science article, Japan Quake Epicenter Was in Unexpected Location, which said the Japanese looked to patterns in the past to determine the future. Therefore they expected a strong earthquake in the south where the Phillipine plate is overdue for a massive event.

Japan has been expecting and preparing for the “big one” for more than 30 years. But the magnitude-9.0 temblor that struck March 11 — the world’s fourth biggest quake since 1900 — wasn’t the catastrophe the island nation had in mind. The epicenter of the quake was about 80 miles east of the city of Sendai, in a strip of ocean crust previously thought unlikely to be capable of unleashing such energy. “This area has a long history of earthquakes, but [the Sendai earthquake] doesn’t fit the pattern,” says Harold Tobin, a marine geophysicist at the University of Wisconsin-Madison. “The expectation was high for a 7.5, but that’s a hundred times smaller than a 9.0.”

It sounds to me like, if in the United States the most powerful earthquake in the area of a nuclear reactor was a 7.5 magnitude event, then a 9.0 could surprise those running it. Given a 9.0 is a hundred times more powerful and a broken reactor so dangerous, I would hope the preparedness is for the larger even where seemingly unlikely.

The Haiti quake was “expected“. However the Chilean, both New Zealand, and the Sendai earthquakes have all sounded unexpected. Of course, living on the Ring of Fire, how can any earthquake be unexpected?

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