Published: November 9, 2006

WASHINGTON, Nov. 8 – With construction of many new nuclear reactors under discussion, the Nuclear Regulatory Commission is grappling with the question of whether they should be designed to withstand a Sept. 11-style airplane attack.

The commission has told its staff to study the vulnerabilities of the four new reactor designs, two of which it has already approved. But it has decided not to make the nuclear power industry meet security requirements any tougher than those for existing plants, which were designed before suicide airliner attacks, and even before the development of such airplanes.

Planes are not on the list of weapons that reactors must be prepared to survive. One of the five commissioners, Gregory B. Jaczko, has called for the panel to require design changes to reduce vulnerability, but the other four seem unpersuaded.

Speaking about protection against aircraft attacks, Mr. Jaczko said in an interview, “We’ve left it in the hands of Transportation Security Administration, the Federal Aviation Administration and the reactor vendors, who are building these plants, to do what they think is right in this area, and to me that’s clearly not the answer.”

“We should be requiring they design these plants to withstand such attacks,” he said.

One of one of the four new reactor designs, called the European Pressurized Reactor, is advertised as being less vulnerable to planes.

The commission has required that operators of reactors that are already producing electricity plan what steps they would take in case of airplane attacks to mitigate the effect and minimize releases of radiation. Mr. Jaczko said that improving the new designs before concrete was poured could sharply reduce the number of “mitigating actions” the operators would have to take a plane attack.

But another member of the commission, Edward McGaffigan Jr., said, “We think we’ve done enough.”

In analyzing security, nuclear engineers talk about multiple components that an attacker would have to reach and disable, which they call “target sets.” New reactors, Mr. McGaffigan said, have “a terribly complex set of target sets that makes it highly improbable that a terrorist would succeed.”

The commission should not make companies that want licenses to build and operate plants treat an airplane attack the way they would treat an earthquake, flood or other external threat for which they are already designed, he said.

A senior staff member of the commission said: “We want to be able to stand up to answer the logical question: ‘Guys, did you look at the aircraft?’ We want to be able to say yes, and we’re confident that there is no issue, or if there is an issue, we’ve taken appropriate measures.”

The staff member said the commission was stopping short of setting new requirements. He said he could not be identified because he was talking about matters that the five commissioners had not yet settled on.

At the Nuclear Energy Institute, the industry’s trade association, Adrian Heymer, senior director for new plant deployment, said designers had analyzed existing plants and made many changes that cost little but made the new designs more difficult to attack. But, in general, Mr. Heymer said, protecting against terrorism was a government function.

“Refineries, tall buildings, those are the responsibility of federal government to protect,” he said.

The commission is scheduled to meet on Thursday at its headquarters in Rockville, Md., to discuss licensing procedures for new reactors.

At the Union of Concerned Scientists, an advocacy group, David Lochbaum, a nuclear engineer, said that in the early 1980s the commission had convened outside experts to talk about hardening new reactors against plane crashes.

Industry experts, Mr. Lochbaum said, talked about some simple steps. For example, backup electricity generators could be positioned on two sides of the plant instead of in one place. Control rooms could be put in less vulnerable spots, and the pools that hold radioactive spent fuel could be hardened. The studies were classified after the attacks of Sept. 11, 2001, he said.

Representative Edward J. Markey, Democrat of Massachusetts, a critic of the nuclear power industry and the commission, says more should be done. In a statement, Mr. Markey said the commission should not only require design features to protect against airplane attacks but should also consider attacks by large truck bombs.

The commission has required substantial changes at existing reactors but has been reluctant to consider the threat of terrorism in the same way it handles other risks. For example, it has refused to consider the risk of terrorism in environmental impact statements, arguing that in contrast to earthquakes or mechanical failures, it does not know what probability to apply to attacks.

A California group, San Luis Obispo Mothers for Peace, won a decision in the United States Court of Appeals for the Ninth Circuit saying the regulatory commission must consider terrorism.

Pacific Gas & Electric, a California utility, has asked the Supreme Court to hear the case.