A former utility executive and nuclear opponent is raising concerns about the presence of two large underground natural gas pipelines that cross within a few hundred feet of the Indian Point nuclear facility in Buchanan, N.Y.

The nuclear reactors' owner, the pipelines' owner and regulators say the pipelines do not pose a threat.

Paul Blanch, an energy consultant from West Hartford, Conn., filed a petition with the Nuclear Regulatory Commission Monday that questions whether the NRC has properly studied the effects of an explosion of the lines or planned for such an accident. The lines supply New England with a quarter of its daily natural gas needs.

"It's a low probability event," said Blanch of a rupture of one of the pipes. "But the consequences are unimaginable."

Concerns about natural gas pipeline safety have been heightened since a large pipeline in San Bruno, Calif. ruptured and exploded in September, killing eight people and destroying 37 homes. Blanch's fear is that similar explosion and subsequent fire at Indian Point could damage or destroy the cooling and safety systems at the site and lead to a catastrophic nuclear accident.

The pipelines near Indian Point carry about double the amount of natural gas as the San Bruno pipeline.

The NRC licenses that allow the plants' owner, Entergy, to operate the two Indian Point reactors expire in 2013 and 2015. Entergy is in the process of trying to extend those licenses for 20 years, and that process has made Indian Point somewhat of a lightning rod for anti-nuclear advocates, including Blanch.

New York State Attorney General Andrew Cuomo, who is running for governor of New York, opposes extending the licenses because, he says, the plants are too close to heavily populated areas. They are 45 miles from New York City. Blanch has testified in hearings on Cuomo's behalf.

Environmental advocates do not want Entergy's licenses renewed because they say the cooling system used by the plants kills unacceptable numbers of endangered fish like the Atlantic sturgeon and other marine organisms.

David Lochbaum, director of the nuclear safety program at the Union of Concerned Scientists, agrees with Blanch that the pipeline issue needs to be explored. He helped Blanch draft his petition.

"This is not to say that this pipeline is a hazard, there may be a good analysis that shows it is not," said Lochbaum in an interview. "But until these questions are answered it is a potential hazard that needs to be looked into."

Mete Sozen, a professor of structural engineering at Purdue University who studies the ability of reinforced concrete to withstand shocks, said it would be extremely difficult for a fire outside a nuclear containment building to affect the reactor core.

The so-called containment structures that house nuclear reactor vessels are built to withstand extremely high temperatures and pressures. "If there's an explosion nearby, I'd want to be inside a nuclear plant," Sozen says.

Blanch is worried that an explosion and fire sustained by large volumes of natural gas would destroy the systems that power and govern the reactor's cooling system. That, he fears, could lead to a breach of the reactor vessel and the release of radioactive material.

The gas pipelines were installed in the 1950s and 1960s, and predate construction of the nuclear plant. Blanch suspects that changes to the pipelines since their safety was first studied in the late 1960s have not been properly evaluated by the NRC.

The NRC said in a letter to Blanch that it had Entergy evaluate the consequences of a failure of the gas pipelines in August of 2008. In September 2008, Entergy concluded that the pipelines do not pose a safety or security hazard, according to the NRC.

The NRC would not make the details of the study available siting "sensitive information."

Entergy also declined to discuss details. In an email, a spokesperson wrote: "An explosion or a fire involving the pipeline does not pose a hazard to the safe operation of the plant."

Lochbaum says he find it "curious" that the NRC is withholding details of the study. He wrote in an email that if the Entergy evaluation showed that if the pipeline was not a threat, "one would think the NRC would want the world, both good guys and bad guys, to know it."

"Either the alleged expert evaluation does not exist (and therefore cannot be made public)," Lochbaum wrote in another email. "Or it does exist but identifies a hazard to the plant (and therefore cannot be made public)."

The NRC made public a study in 2004 that showed that a natural gas pipeline near a uranium enrichment facility Eunice, New Mexico did not pose a hazard.

And in the past the commission itself has raised concerns about natural gas near nuclear facilities. In 1991 it alerted all nuclear power plant operators to potential hazards after it discovered that natural gas wells were drilled and pipes installed near the Fort St. Vrain nuclear facility in northern Colorado without being properly studied. The plant was closed in 1992.

NRC documents from 1968, when the reactors were being built, say the lines don't pose a threat to the plants in part because automatic shutoff valves near the section that runs near the plant would allow the owner of the gas line to stop the flow of gas within four minutes.

A 1995 NRC document, however, says "automatic shutoff controls have recently been removed from all valve sites" because they had been shutting off gas flow mistakenly. A Spectra spokesperson wrote in an email that those controls were replaced with "more advanced and reliable" controllers.

The company said it would be able to shut off gas in "minutes" but declined to be more specific. The company also declined to say how far away the shutoff controllers are from the section of pipeline that crosses the Indian Point property.

Jim Hall, a pipeline safety expert who served as chairman of the National Transportation Safety Board under President Bill Clinton said that pipelines in a sensitive area like near a nuclear reactor should have a backup system that would kick in if the initial shutoff system failed. "And it should be unacceptable to have pipelines there that are 50 or 60 years old," he said.

Spectra says its safety systems have backup electrical systems that will allow them to be activated even if power is lost. It said systems are monitored at all times from a Houston control center. The age of the pipelines, it said in an email, is "not really the issue" because they undergo regular maintenance and inspection.

Spectra says 1.45 billion cubic feet of gas per day flows in the lines near Indian Point, or about 1 million cubic feet per minute. That's double the rate of gas flow that escaped in the San Bruno disaster.

A 2010 study of the feasibility of installing a new cooling system at Indian Point estimated that it would cost $13.8 million to move the gas pipelines.

Blanch spent 20 years at Northeast Utilities, where he was a nuclear operations engineer. While there, he raised safety concerns about Connecticut's Millstone generating station. He was fired by the company, but after the NRC substantiated Blanch's concerns he was rehired and defended Millstone's safety procedures. He believes that the NRC does not enforce nuclear safety strictly enough, and he is especially concerned with the degradation of older reactors like the ones at Indian Point.

The type of petition filed by Blanch, called a 2.206 petition, can be filed by any concerned member of the public. As of the end of August, there were 11 such petitions under review by the NRC. The NRC is expected to decide within a month whether or not to investigate Blanch's claims.