LACEY TOWNSHIP, N.J. — Federal regulators have been working closely with the nuclear power industry to keep the nation’s aging reactors operating within safety standards by repeatedly weakening those standards or simply failing to enforce them, an investigation by the Associated Press has found.

Time after time, officials at the US Nuclear Regulatory Commission have decided that original regulations were too strict, arguing that safety margins could be eased without peril, according to records and interviews.

The result? Rising fears that these accommodations by the NRC are significantly undermining safety and inching the reactors closer to an accident that could harm the public and jeopardize the future of nuclear power in the United States.

Examples abound. When valves leaked, more leakage was allowed — up to 20 times the original limit. When rampant cracking caused radioactive leaks from steam generator tubing, an easier test of the tubes was devised so plants could meet standards.

Failed cables. Busted seals. Broken nozzles, clogged screens, cracked concrete, dented containers, corroded metals, and rusty underground pipes — all of these and thousands of other problems linked to aging were uncovered in the AP’s yearlong investigation.

And all of them could escalate dangers in the event of an accident.

Yet despite the many problems linked to aging, not a single official body in government or industry has studied the overall frequency and potential impact on safety of such breakdowns in recent years, even as the NRC has extended the licenses of dozens of reactors.

Industry and government officials defend their actions and say that no chances are being taken. But the AP investigation found that with billions of dollars and 19 percent of America’s electricity supply at stake, a cozy relationship prevails between the industry and its regulator, the NRC.

Records show a recurring pattern: reactor parts or systems fall out of compliance with the rules; studies are conducted by the industry and government; and all agree that existing standards are “unnecessarily conservative.’’

Regulations are loosened, and the reactors are back in compliance.

“That’s what they say for everything, whether that’s the case or not,’’ said Demetrios Basdekas, an engineer retired from the NRC. “They say ‘We have all this built-in conservatism.’ ’’

The ongoing crisis at the stricken, decades-old Fukushima Daiichi nuclear facility in Japan has focused attention on the safety of plants elsewhere in the world; it prompted the NRC to look at US reactors, and a report is due in July.

But the factor of aging goes far beyond the issues posed by the disaster at Fukushima.

Commercial nuclear reactors in the United States were designed and licensed for 40 years. When the first ones were being built in the 1960s and 1970s, it was expected that they would be replaced with improved models before those licenses expired.

But that never happened.

Instead, 66 of the 104 operating units have been relicensed for 20 more years, mostly with scant public attention. Renewal applications are under review for 16 other reactors.

By the standards in place when they were built, these reactors are old. As of today, 82 reactors are more than 25 years old.

AP found proof that aging reactors have been allowed to run less safely to prolong operations. As equipment has approached or violated safety limits, regulators and reactor operators have loosened or bent the rules.

Last year, the NRC weakened the safety margin for acceptable radiation damage to reactor vessels — for a second time.

The standard is based on a measurement known as a reactor vessel’s “reference temperature,’’ which predicts when it will become dangerously brittle and vulnerable to failure. Over the years, many plants have violated or come close to violating the standard.

As a result, the minimum standard was relaxed first by raising the reference temperature 50 percent, and then 78 percent above the original — even though a broken vessel could spill its radioactive contents into the environment.

“We’ve seen the pattern,’’ said nuclear safety scientist Dana Powers, who works for Sandia National Laboratories and also sits on an NRC advisory committee. ‘ ‘They’re . . . trying to get more and more out of these plants.’’

AP collected and analyzed government and industry documents — including some that had never been released. The study looked at both types of reactor designs: pressurized water units that keep radioactivity confined to the reactor building, and the less-common boiling water types, like those at Fukushima, which send radioactive water away from the reactor to drive electricity-generating turbines.

© Copyright 2011 Globe Newspaper Company.