U.S. Dropped Nuclear Rule Meant to Avert Hydrogen Explosions

By MATTHEW L. WALD/NYT

The Three Mile Island nuclear plant in Pennsylvania on Monday, 32 years to the date after an accident there. When hot fuel interacted with steam there, the plant's suffered a hydrogen explosion.Associated Press The Three Mile Island nuclear plant in Pennsylvania on Monday, 32 years to the day after an accident there. When hot fuel interacted with steam there, a reactor suffered a hydrogen blast.

The Nuclear Regulatory Commission has allowed reactors to phase out some equipment that eliminates explosive hydrogen, the gas that blew up the outer containments of three reactors at the Fukushima Daiichi in Japan. The commission says it judged that at the American plants, the containments were strong enough that the equipment was not needed or other methods would do.

After the Three Mile Island accident in 1979, many reactors were required to install “hydrogen recombiners,” which attach potentially explosive hydrogen atoms to oxygen to make water instead. At Three Mile Island, engineers learned that hot fuel could interact with steam to give off hydrogen. That caused the plant’s reactor to suffer a hydrogen explosion, although it did not seriously damage its containment. By contrast, the secondary containments at Fukushima Daiichi blew apart when hydrogen detonated inside them.

The change in commission policy was pointed out this week by a nuclear safety critic, Paul M. Blanch, who said that he had been involved in installing such equipment at Millstone 3, a nuclear reactor in Waterford, Conn.

“Post-Three Mile Island, they were considered very important to safety,’’ Mr. Blanch said. He accused the Nuclear Regulatory Commission of having “gutted the rule’’ because the industry wanted to save money.

But Eliot Brenner, a spokesman for the commission, said that as the commission analyzed its rules to determine which ones actually improved safety and which did not, it had found the equipment was unnecessary.

More than half the American reactors have applied to drop the hydrogen recombiners from their technical specifications, but many of those plants still keep them operable nonetheless, according to the commission.

Commission officials said they have allowed reactors to rely on simpler, easier-to-maintain equipment instead of the recombiners.
Indian Point 2 and 3, in Buchanan, N.Y., and Millstone 2 and 3 in Waterford, Conn., are among the reactors that were allowed to delete hydrogen recombiners from their formal “technical specifications,” the government list of equipment that must be inspected, tested and maintained within certain limits for the reactor to be allowed to operate.

But James F. Steets, a spokesman for Indian Point, said that Units 2 and 3 there each had two recombiners and that one alone could eliminate all the hydrogen in a major accident.

Millstone 2 and 3, near New London, are in the same category; the equipment should still be operable, but having it in working order is no longer a condition required by the license, said Kenneth A. Holt, a spokesman for Dominion, which owns the reactors now.

The Nuclear Regulatory Commission said that it changed the rules in 2003 as part of an “ongoing effort to risk-inform its regulations,’’ meaning adjust its rules to reflect actual risk to reactors. At issue were “design basis accidents” and “severe” accidents, which are worse.

“They weren’t needed for design basis accidents and they didn’t help with severe accidents,’’ Mr. Brenner said.

Depending on the type of reactor, the commission now requires a variety of other precautions. General Electric models of the type used at Fukushima, which are also common in the United States, must pump their primary containments full of nitrogen gas instead of air, for example.

Because hydrogen requires that oxygen be in the air to detonate, this “inerting” of the primary containments is a way of preventing explosions. And some plants have to have “igniter systems” that would burn off hydrogen before it could build up.

The recombiners and a great deal of other equipment and safety procedures will be re-examined as part of a 90-day review that the commission is conducting after the Fukushima accident, Mr. Brenner said.

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