ROCKVILLE, Md. - When commercial nuclear power was getting its start in the 1960s and 1970s, industry and regulators stated unequivocally that reactors were designed only to operate for 40 years. Now they tell another story - insisting that the units were built with no inherent life span, and can run for up to a century, an Associated Press investigation shows.

By rewriting history, plant owners are making it easier to extend the lives of dozens of reactors in a relicensing process that resembles nothing more than an elaborate rubber stamp.

As part of a yearlong investigation of aging issues at the nation's nuclear power plants, the AP found that the relicensing process often lacks fully independent safety reviews. Records show that paperwork of the U.S. Nuclear Regulatory Commission sometimes matches word-for-word the language used in a plant operator's application.

Also, the relicensing process relies heavily on such paperwork, with very little onsite inspection and verification.

And under relicensing rules, tighter standards are not required to compensate for decades of wear and tear.

So far, 66 of 104 reactors have been granted license renewals. Most of the 20-year extensions have been granted with scant public attention. And the NRC has yet to reject a single application to extend an original license. The process has been so routine that many in the industry are already planning for additional license extensions, which could push the plants to operate for 80 years, and then 100.

Regulators and industry now contend that the 40-year limit was chosen for economic reasons and to satisfy antitrust concerns, not for safety issues. They contend that a nuclear plant has no technical limit on its life.

But an AP review of historical records, along with interviews with engineers who helped develop nuclear power, shows just the opposite: Reactors were made to last only 40 years.

Period.

The record also shows that a design limitation on operating life was an accepted truism.

In 1982, D. Clark Gibbs, chairman of the licensing and safety committee of an early industry group, wrote to the NRC that "most nuclear power plants, including those operating, under construction or planned for the future, are designed for a duty cycle which corresponds to a 40-year life."

And three years later, when Illinois Power Co. sought a license for its Clinton station, utility official D.W. Wilson told the NRC on behalf of his company's nuclear licensing department that "all safety margins were established with the understanding of the limitations that are imposed by a 40-year design life."

One person who should know the real story is engineering professor Richard T. Lahey Jr., at Rensselaer Polytechnic Institute in Troy, N.Y. Lahey once served in the nuclear Navy. Later, in the early 1970s, he helped design reactors for General Electric Co.; he oversaw safety research and development.

Lahey dismisses claims that reactors were made with no particular life span. "These reactors were really designed for a certain lifetime," he said. "What they're saying is really a fabrication."

NUCLEAR LIFE RENEWED

Relicensing is a lucrative deal for operators. By the end of their original licenses, reactors are largely paid for. When they're operating, they're producing profits. They generate a fifth of the country's electricity.

New ones would each cost billions of dollars and take many years for approval, construction and testing. Local opposition may be strong.

Already there is controversy about the safety of a next-generation design. Even before the nuclear crisis at the Fukushima Dai-ichi complex in Japan, only a handful of proposed new reactors in the U.S. had taken the first steps toward construction.

Solar and wind power are projected to make very limited contributions as electrical demand rises about 30 percent by 2035. So keeping old plants operating makes good business sense.

But it's challenging to keep existing plants safe and up to date.

The NRC has indicated that safety improvements are likely in the aftermath of melted fuel in the Japanese reactors in March. NRC inspectors have found some problems with U.S. equipment and procedures. But the agency says all sites are ready to deal with earthquakes and flooding. The NRC also has formed a task force to investigate further and report back in July. Both the task force and the NRC chairman have already suggested that changes will be needed.

Meanwhile, license renewals, which began in 2000, continue. The process essentially requires a government-approved plan to manage wear. These plans entail more inspection, testing and maintenance by the operator, but only of certain equipment viewed as subject to deterioration over time.

The plans focus on large systems like reactor vessels. It is assumed that existing maintenance is good enough to keep critical smaller parts - cables, controls, pumps, motors - in good working order for decades more.

Some modernization has been put in place - upgrades on fire-prevention measures and electronic controls, for example. But many potential improvements are limited by the government's so-called "backfit rule." The provision exempts existing units from safety improvements unless such upgrades bring "a substantial increase" in public protection.

Even with required maintenance, aging problems keep popping up.

During its Aging Nukes investigation, the AP conducted scores of interviews and analyzed thousands of pages of industry and government records, reports and data.

The documents show that for decades compromises have been made repeatedly in safety margins, regulations and emergency planning to keep the aging units operating within the rules. The AP has reported that nuclear plants have sustained repeated equipment failures, leading critics to fear that the U.S. industry is one failure away from a disaster.

INDUSTRY, U.S. AS PARTNERS

Despite the aging problems, relicensing rules prohibits any overall safety review of the entire operation. More conservative safety margins are not required in anticipation of higher failure rates in old plants, regulators acknowledge.

The approach has turned relicensing reviews into routine approvals.

"Everything I've seen is rubber-stamped," said Joe Hopenfeld, an engineer who worked on aging-related issues at the NRC before retiring in 2008. He has since worked for groups challenging relicensing.

Numerous reports from the NRC's Office of Inspector General offer disturbing corroboration of his view.

For example, in 2002 the inspector general wrote: "Senior NRC officials confirmed that the agency is highly reliant on information from licensee risk assessments." Essentially that means the industry tells the NRC how likely an accident is and the NRC accepts the analysis.

Five years later, in a relicensing audit, the inspector general complained of frequent instances of "identical or nearly identical word-for-word repetition" of the plant applications in NRC reviews. The inspector general worried that the repetition indicated superficial reviews that went through the motions, instead of thorough and independent examinations.

The problems went beyond paperwork. The inspector general found that the NRC reviews usually relied on the plants to report on their operating experience, but the agency didn't independently verify the information.

NRC spokesman Eliot Brenner said staffers have now agreed to use their own words in their reviews of relicensing applications.

Christopher Grimes, former director of license renewal at the NRC, acknowledges that the agency "has to rely much more on the contents of the applications ... over direct inspection."

He blames budget constraints, but others view relicensing as a charade. Clean Ocean Action unsuccessfully challenged relicensing at the Oyster Creek plant in New Jersey, but chief scientist Jennifer Sampson said, "We really knew it was a waste of time."