Updated

Three U.S. senators, alarmed by findings of an Associated Press investigation about aging problems at the nation's nuclear power plants, asked Thursday for a congressional investigation of safety standards and federal oversight at the facilities.

The request by Democrats Barbara Boxer of California and Sheldon Whitehouse of Rhode Island and independent Bernard Sanders of Vermont builds on increased public concern about nuclear safety in recent months — an outcry unlike anything since the Chernobyl nuclear accident in 1986.

Public interest first spiked after the March accident at the Fukushima Dai-ichi nuclear plant in Japan. Concern has been heightened this week as the AP began releasing the results of a yearlong investigation into aging related safety problems at the 104 reactors operating in the United States.

That's led activists, politicians, critics and safety watchdogs to say they hope to turn the public focus more sharply onto the industry in America and broader regulatory problems at the U.S. Nuclear Regulatory Commission. One after another, they said they hope the result will be tougher relicensing and safety standards, safer storage of spent fuel and better disaster planning.

Janet Tauro, of Brick, N.J., co-founder of Grandmothers, Mothers, and More for Energy Safety who lives near the Oyster Creek nuclear plant, said the latest developments have led her to conclude "the light is really starting to shine on a very closed regulatory agency."

Senators Boxer, Whitehouse and Sanders asked for the oversight investigation by the Government Accountability Office. Boxer chairs the Senate Committee on Environment and Public Works.

New Jersey's two Democratic senators, Frank R. Lautenberg and Robert Menendez, made a similar request of the GAO earlier this week.

In recent months, public anxiety over nuclear power has "peaked incredibly," said engineer Paul Blanch, an industry whistleblower who later returned to work on improving safety. He is now fighting relicensing applications at four sites.

"I was fighting the world, and now I'm only fighting half the world," Blanch said.

Visits to the website of Fairewinds Associates, a nuclear safety consultant in Burlington, Vt., have exploded from about 80 a day to 7,000 since the Japanese accident, according to chief engineer, Arnie Gundersen. Site visits rose about another 10 percent when the AP series started on Monday.

The AP's four-part investigative series shows that government and industry have been working in tandem to weaken safety standards to keep aging reactors within the rules. The series also found that there have been leaks of radioactive tritium, often from corroded underground piping, at three-quarters of U.S. commercial nuclear power sites.

In a GAO report released Tuesday by Democratic Reps. Edward J. Markey of Massachusetts and Peter Welch of Vermont, the watchdog agency concluded that nuclear power plant operators haven't figured out how to quickly find the underground leaks, which often go undetected for years.

The AP series, which continues next week with an examination of explosive population growth around the 65 sites that house the reactors, comes three months after a tsunami born from an earthquake caused a nuclear crisis at the Fukushima Dai-ichi nuclear complex in Japan. The March 11 natural disaster swamped backup generators, disabled cooling systems, caused fuel melts and explosions, and released vast amounts of radiation into the grounds and sea.

The NRC has said it disagrees with AP's conclusions, but welcomes the attention the stories have generated to nuclear plant safety. The agency defended its standards and approach to safety.

The industry's Nuclear Energy Institute criticized AP's overall findings and "selective, misleading reporting" on U.S. nuclear power plant safety.

Public concern about nuclear safety reached a zenith after the Three Mile Island accident in 1979 and Chernobyl.

However, public interest has slipped since initial rounds of safety improvements after those accidents. Originally licensed for 40 years, 66 of U.S. 104 reactors have been relicensed for another two decades. Safety regulators at the NRC have never denied a request. Few requests have met much opposition. And 16 relicensing applications are pending.

Randy Voller, mayor of the small town of Pittsboro, N.C., said people are now more focused both on existing plants and where new ones might be located. His town lies just beyond the 10-mile zone where evacuation plans have been made for an accident at the Shearon Harris nuclear plant.

"The plants weren't made to last forever," he said. "We are more aware of the risks than we were before."

Steven Kerekes, a spokesman for the Nuclear Energy Institute, said heightened public concern is "understandable," given the Japanese accident and heavy news coverage.

But he said the relicensing process, which can take years, is "properly focused," that fire requirements are already strict, and the industry has been moving spent fuel into dry storage since the mid-1980s.

Despite such assurances, safety activists are laying plans to mobilize the public.

The website of Beyond Nuclear, an anti-nuclear group, has been bombarded with tens of thousands of additional visitors in recent months, according to Paul Gunter, the group's director of reactor oversight.

He said nuclear safety has primarily concerned specialists in recent years. "Now it's mothers and housewives who are concerned about fallout from Fukushima and from reactors in their own neighborhood," Gunter said.

Tauro said an independent safety assessment — beyond that of the NRC — should be carried out before any other reactors are relicensed. She said no federal loan guarantees should be offered to new reactors.

Bernard Weinstein, associate director of the Maguire Energy Institute at Southern Methodist University, predicted an eventual tightening of regulations as a result of the public pressure.

Bill Corcoran, president of Nuclear Safety Review Concepts Corp. in Windsor, Conn., and other safety analysts have argued that plants need better designs for fire protection, more spent fuel stored inside dry casks instead of cooling pools, and planning that anticipates more severe fires, earthquakes, tsunamis, tornados and extended power outages — and combinations of them.

Alarmed by the AP findings on tritium, Annette Quijano, a member of the New Jersey state Assembly, said she's drafting a legislative resolution asked for stronger federal oversight of the state's four commercial nuclear reactors.

"Our reactors are obviously not aging well and it would seem that it is only a matter of time until the public is put at serious risk due to a structural failure, a natural disaster or, God forbid, an act of terror," she said.

Relicensing requests are pending at the Hope Creek and Salem plants in New Jersey. Joe Delmar, spokesman for owner PSE&G Nuclear, said the NRC is already "a very strict regulator." He said the agency has extensively reviewed the company's plan to maintain aging systems.

NRC chairman Gregory Jaczko has defended his agency as an effective regulator but also hinted at improvements. The commission expects to issue a report in July on a broad review of safety undertaken in the wake of the Japanese accident.

Speaking Tuesday in Vienna, Jaczko said plants are safe but added: "I believe there is a likelihood that the agency will need to make some changes." He cited several problem areas that fed the disaster in Japan: extended power outages, spent fuel pools and emergency planning.

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The AP National Investigative Team can be reached at investigate(at)ap.org