“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.