In the fall of 2007, workers at the Byron nuclear power plant in Illinois were using a wire brush to clean a badly corroded steel pipe - one in a series that circulate cooling water to essential emergency equipment - when something unexpected happened: The brush poked through.
The resulting leak caused a 12-day shutdown of the two reactors for repairs.
The plant's owner, the Exelon Corp., had long known that corrosion was thinning most of these pipes. But rather than fix them, it repeatedly lowered the minimum thickness it deemed safe. By the time the pipe broke, Exelon had declared that pipe walls just three-hundredths of an inch thick - less than one-tenth the original minimum thickness - would be good enough.
Though no radioactive material was released, safety experts say that if enough pipes had ruptured during a reactor accident, the result could have been a nuclear catastrophe at a plant just 100 miles west of Chicago.
Exelon's decisions occurred under the noses of on-site inspectors from the federal Nuclear Regulatory Commission. No documented inspection of the pipes was made by anyone from the NRC for at least the eight years preceding the leak, according to an investigation by the commission's inspector general.
Exelon's penalty? A reprimand for two low-level violations - a tepid response all too common at the NRC, said George A. Mulley Jr., a former investigator with the inspector general's office who led the Byron inquiry.
Critics have long painted the commission as well-intentioned but incapable of keeping close tabs on an industry to which it remains closely tied. The concerns have greater urgency because of the crisis at the Fukushima Dai-ichi plant in Japan, which many experts say they suspect was caused as much by lax government oversight as by a natural disaster.
The Byron pipe leak is just one recent example of the agency's shortcomings, critics say. It has also taken nearly 30 years for the commission to get effective fireproofing installed in plants after an accident in Alabama. The number of civil penalties paid by licensees has plummeted nearly 80 percent since the late 1990s.
Although the agency says plants are operating more safely today than they were at the dawn of the nuclear industry, when shutdowns were common, safety experts, critics in Congress and even the agency's own internal monitors say the NRC is prone to dither when companies complain that its proposed actions would cost time or money.
The promise of lucrative industry work after officials leave the commission probably doesn't help, critics say.
Now, as most of the country's 104 aging reactors are applying for, and receiving, 20-year extensions from the NRC on their original 40-year licenses, reform advocates say a thorough review of the system is urgently needed.
Peter Bradford, a former NRC commissioner who now teaches at Vermont Law School, said the nuclear industry had implicitly or explicitly supported every nomination to the commission until Gregory B. Jaczko's in 2005.
Jaczko, who was elevated to chairman by President Barack Obama in 2009, had previously worked for both Rep. Edward J. Markey, the Massachusetts Democrat and longtime critic of the nuclear industry, and Sen. Harry Reid, the Nevada Democrat and Senate majority leader who sought to block a nuclear waste repository in his state.
Jaczko acknowledges the agency needs to move faster on safety issues. But he defends its record. "I certainly feel very strongly that this is an independent regulator that will make what it thinks are the right decisions when it comes to safety," he said.
David Lochbaum, a frequent critic of the NRC who recently worked as a reactor technology instructor there, said the agency too often rolled the dice on safety: "The only difference between Byron and Fukushima is luck."
When the industry set out in the 1980s to prove that the original 40-year licenses on its aging plants could be safely renewed for 20 years, Yankee Rowe in Massachusetts and Monticello in Minnesota were offered as test cases.
The NRC's criteria for relicensing essentially required that operators prove that they were in compliance with their current license and that they had an adequate plan to manage the aging equipment. That tripped up Yankee Rowe's bid, because inspectors looking at its current operations found serious flaws in its reactor vessel. The plant shut down with eight years left on its original license.
In 1992, Northern States Public Power, owner of the Monticello plant, complained that the agency was examining details beyond those necessary for license renewal.
With billions of dollars of revenue and investment at stake for each plant, the NRC changed the rules in 1995, scrapping the requirement that operators prove they were complying with their current license. Instead, the renewal process would focus only on the aging management plan.
James Riccio, a nuclear policy analyst with Greenpeace, said, "The NRC rule change gutted a substantive process and replaced it with a rubber stamp. They placed industry profits ahead of public safety."
License renewal is still arduous. According to a 2007 audit by the inspector general's office, an operator typically spends two years and up to $20 million preparing an application, and the commission on average spends two years and $4 million reviewing it.
But the audit concluded it was often impossible to know whether the agency had conducted an independent review. In some cases, long passages in the commission's assessment of a renewal appeared to have been copied and pasted directly from the application.
What frustrates some critics is that the NRC has the resources - a staff of 4,000 and one of the highest densities of Ph.D.s in government - to do a better job. Indeed, there are examples of the commission making tough decisions.
In 2008, workers at the Oconee plant in South Carolina discovered a crucial line in the cooling system at Reactor Unit 1 was blocked by a broken gasket. The workers fixed it, and the reactor was restarted.
The two NRC inspectors assigned full time to Oconee quickly began asking why Duke Energy, the operator, wasn't inspecting corresponding valves and lines at the plant's other two reactors. Duke said the clogging was isolated and a blocked line could be bypassed in a pinch.
In February 2010, when the company finally agreed to look at the other two reactors, it discovered that the lines there had the same problem and that the bypass option would never have worked.
The commission issued a "yellow finding" to Duke, its second-highest category of safety problem. The finding, which is rarely imposed, generally brings far more NRC and media scrutiny, and can have financial implications for the company on Wall Street.