American experts are monitoring nuclear facilities in China's earthquake zone, officials said Friday, after France's nuclear watchdog reported that some had suffered minor damage.

The French Institute for Radiological Protection and Nuclear Safety said Chinese authorities "reacted well" to the quake and immediately shut down nuclear sites for inspection.

Thierry Charles, the group's director of plant safety, said China's nuclear safety agency, NNSA, had reported no leaks of radioactivity since the quake.

He said the Chinese reported "light damage" to older nuclear facilities that were being dismantled before the quake, noting that seismic construction codes were less strict when those sites were built. China did not specify which facilities had damage, he said.

China has a research reactor, two nuclear fuel production sites and two atomic weapons sites in Sichuan province, where the magnitude-7.9 quake struck Monday, the French agency said. All were between 40 and 90 miles from the epicenter.

French authorities do not yet have a full picture of any possible damage at the nuclear weapons sites, where information is more closely guarded, Charles said.

"At this stage, I don't think there were any leaks, because they would have reported them by now. The worst to worry about now is degradation of buildings, cracks, this kind of thing," he said.

U.S. officials are monitoring China's nuclear facilities in the quake zone, State Department spokesman Sean McCormack said. He said he had no information about any damage.

Wang Baodong, spokesman for the Chinese Embassy in Washington, said he had no information about the state of the atomic sites. But he told reporters the Chinese government was "preparing for every consequence" as it worked to rescue survivors and repair damage.

Nuclear experts said there several possibilities if any significant damage occurred at the plants, at least one of which is alongside a river. A radioactive leak could cause environmental harm, while internal damage could set back China's nuclear modernization, they said.

Mianyang, an industrial city of 700,000 people that is the headquarters of China's nuclear weapons design industry, was on the edge of the disaster area. The site has been likened to the U.S. nuclear facility at Los Alamos, N.M.

The plutonium production reactor at Guangyuan, China's largest, is also in the quake zone.

"Damage to these plants could potentially be a serious issue for the Chinese government," said Hans Kristensen, a nuclear arms expert at the Federation of American Scientists.

He said the reactor at Guangyuan is "at the center of China's fissile material production.

"If there is damage to (the reactor), it would disrupt China's warhead maintenance capabilities," Kristensen said. "That could have impacts for several years."

Matthew Bunn, a senior researcher at Harvard University's Project on Managing the Atom, said the risk of radioactive leaks depended mostly on how the facilities were designed, details of which are known only by the Chinese government.

"Only in the reactor's case would there likely be any significant danger of some kind of radioactive release that would affect a large area. And how big that danger is depends enormously on specifics of the reactor's seismic design that are not well known outside the Chinese nuclear weapons program," Bunn said.

Jeffrey Lewis, director of the Nuclear Strategy and Nonproliferation Initiative at the New America Foundation who visited Mianyang last summer, said the buildings were designed to withstand earthquakes.

"I would be surprised if there were any human impact," said Lewis, referring to radioactive leaks. "If anything, there is a possibility for structural damage."

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Associated Press writer Foster Klug in Washington contributed to this report.