At U.S. Nuclear Sites, Preparing for the Unlikely

By JOHN M. BRODER, MATTHEW L. WALD and TOM ZELLER Jr.
New York Times

WASHINGTON - American nuclear safety regulators, using a complex mathematical technique, determined that the simultaneous failure of both emergency shutdown systems that are designed to prevent a core meltdown was so unlikely that it would happen once every 17,000 years.

The American people, and the regulators whose job it is to protect them from a catastrophic nuclear accident, are watching the unfolding events at a complex of crippled reactors in Japan with foreboding and an overriding question: Can it happen here?

The answer - probably not - from the Nuclear Regulatory Commission is meant to reassure. But as the New Jersey accidents in 1983, which did not result in any core damage or release of radiation, show, no one can predict what might upend all the computer models, emergency planning and backup systems designed to eliminate those narrow theoretical probabilities or mitigate their effects.

"We can never say that that could never happen here," said Anthony R. Pietrangelo, senior vice president and chief nuclear officer at the Nuclear Energy Institute, the industryís main trade association. "It doesnít matter how you get there, whether itís a hurricane, whether itís a tsunami, whether itís a seismic event, whether itís a terrorist attack, whether itís a cyberattack, whether itís operator error, or some other failure in the plant ó it doesnít matter. We have to be prepared to deal with those events."

The threats considered most serious by nuclear engineers are problems that lead to a loss of power. Lack of power to run cooling systems for the reactor core and for spent-fuel ponds led to the explosions and release of radiation at the Fukushima Daiichi nuclear complex in Japan.

American nuclear facilities have backup power systems, and backups to those. All plants are required to have batteries to provide power in the event of a loss of power and failure of backup generators. In the United States, 93 of the 104 operating reactors have batteries capable of providing power for four hours; the other 11 have eight-hour batteries. Fukushima had eight-hour batteries. It wasnít enough

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