“Extensive evaluations are underway to validate design capabilities and vulnerabilities . . . for events such as earthquakes, flooding, and extended Station Blackouts,” the slides said. It noted that after the Sept. 11, 2001, attacks, the company had bought diesel-driven pumps and figured out how to inject water from nearby sources into the reactor.
The crisis in Japan has spawned new looks at — and revived old debates about — U.S. nuclear plants and how prepared they are for natural or man-made disasters. The GE boiling-water reactor design, found in 23 U.S. nuclear plants, has come under new scrutiny. And because the Japanese crisis started with a loss of grid and generator power, backup electrical systems are being looked at anew.
“Any time something like this happens, you have to be an idiot not to look at lessons learned,” said Michael W. Golay, professor of nuclear engineering at the Massachusetts Institute of Technology. “It comes down to what level you want to set performance standards to provide against a rare event. Every society sets a limit, and the question is just where you want to set the limit.”
Five out of the six reactors at the Fukushima Daiichi nuclear complex share the design GE created decades ago to serve as a smaller, less expensive alternative to what competitors were offering.
Officials have called on plant operators to make major improvements to the GE model — known as Boiling Water Reactor Mark 1 — to help it hold up in an extreme accident.
In 1975, a Nuclear Regulatory Commission report cast doubt on the strength of the system used to capture excess steam inside the reactor or hot materials in an emergency. In response, regulators required each Mark 1 plant operator to fortify the reactor’s torus — the donut-shaped tube at the bottom of the reactor that condenses steam and other substances into a pool of water.
Japanese officials have said that Tuesday’s explosion at Fukushima Daiichi unit 2 occurred in or near the torus and seems to have opened a route for water and radioactive substances to escape the thick-walled primary containment vessel.
In 1979, the Three Mile Island accident prompted another look at the Mark 1. Regulators examined the reactor’s ability to handle a buildup of hydrogen gas — which led to an explosion inside the Three Mile Island containment structure — and ordered plant operators to install vents.
At Fukushima Daiichi, those vents led to an outer building. In three of those buildings, filters and fans failed; in two of them, hydrogen-fueled explosions have destroyed the outer buildings.
An NRC spokesperson said all 23 GE boiling water reactors in the United States have satisfied regulators’ earlier concerns about the ability to withstand a severe incident.
Entergy, based in New Orleans, runs three reactors with the BWR Mark 1 design.
“Obviously, I think they can hold up over time,” said John Herron, president, chief executive and chief nuclear officer of Entergy Nuclear. “They’re an excellent design.”
Herron added that Entergy’s plants have several backup power sources, including diesel generators.
“We drill on that,” Herron said. “We make sure our plants are absolutely ready.”
“To be fair to General Electric and that design, I don’t know of any other designs that would’ve fared much better,” said David Lochbaum, director of the Nuclear Safety Project at the Union of Concerned Scientists. “Their biggest problem wasn’t the containment design. It was the loss of power.”
Harold Denton, the top safety official at the NRC who raised questions about the Mark 1 in the 1980s, said he was monitoring the events at the Fukushima Daiichi plant from his home in Knoxville, Tenn.
“It’s only after [Three Mile Island] that I and everyone else got serious,” said Denton, who has since retired. “Suppose it’s a really severe accident. How do these [reactors] compare?”
Denton said the industry made adjustments after the NRC raised questions. “They accepted what was proposed, and there were changes made,” Denton said. The reactors “just weren’t designed to deal with a core meltdown because that seemed to be too unlikely a proposal at the time.”
The Japan crisis, which began with an electricity outage, has also drawn attention to backup power. Experts say that the tsunami either waterlogged backup diesel generators, destroyed fuel tanks or flooded switch gears needed to hook up the generators — or all three.
Then there’s the human element.
“I worry about human errors in the ordinary running of the plants because that tends to be how you get into trouble,” said Golay, the MIT professor.