The nuclear crisis in Japan has prompted a re-examination of the safety net for nuclear power in the United States, with former regulators and safety advocates warning that gaps in the nation's regulatory armor could leave Americans similarly vulnerable to disaster.

The Nuclear Regulatory Commission, the federal oversight body tasked with licensing and inspecting civilian nuclear facilities, too frequently relies on reports from the industry itself in monitoring for trouble, and is too lenient in meting out sanctions when it encounters violations, these critics say.

Though the commission posts inspectors at every plant, several independent and government reports note that these on-site observers document only a fraction of the events they observe on a daily basis.

"This co-dependent relationship between the industry and the NRC is stronger than the SEC and their relationship with Wall Street," said Robert Alvarez, a former advisor in the Department of Energy, and now a senior scholar on nuclear policy at the Institute for Policy Studies in Washington. The SEC (Securities and Exchange Commission) is oft-blamed for failing to adequately police the financial system in the years before the recent banking crisis.

A report released Thursday by the Union of Concerned Scientists, an environmental safety group, documents a series of inconsistent approaches used by the Nuclear Regulatory Commission when encountering major problems at plants over the last year, making enforcement appear haphazard.

In one case, at the Indian Point Nuclear Power Plant in New York, NRC inspectors allowed a leaking water containment system to persist for more than 15 years despite documentation of the problem, according to the report. A spokesman for Entergy, the utility that runs Indian Point, said the leaking is not "ideal," but that the water stays on site and does not pose a risk to the environment.

At the Calvert Cliffs plant in Maryland, a leaking roof that workers had known about for eight years caused an electrical short in 2010, forcing a shutdown of two reactors.

A spokeswoman for the NRC said that officials at the oversight agency were aware of the report, but had not been able to review it in depth because of attention to the events in Japan.

"The NRC remains confident that our Reactor Oversight Program, which includes both on-site and region-based inspectors, is effectively monitoring the safety of U.S. nuclear power plants," the spokeswoman wrote in an e-mailed statement.

The report from the Union of Concerned Scientists asserts that the NRC is only able to audit about 5 percent of activities at nuclear plants across the country in any given year, and that regulators are often too focused on the minutiae of individual violations instead of addressing systemic problems at a plant that may have led to deficiencies.

"The NRC must draw larger implications from narrow findings for the simple reason that it audits only about 5 percent of activities at every nuclear plant each year," wrote David Lochbaum, a nuclear engineer who authored the report for the Union of Concerned Scientists. "Each NRC finding therefore has two important components: identifying a broken device or impaired procedure, and revealing deficient testing and inspection regimes that prevented workers from fixing a problem before the NRC found it."

The report looked at 14 "near-misses" over the past year - events that required a special investigations team from the NRC to do a detailed inspection after a problem occurred. Many of the issues involved electrical shorts or deficient equipment at various plants that led to fires or unplanned shutdowns of the reactors.

One of the more egregious examples cited involved the HB Robinson plant in South Carolina, operated by Progress Energy, which had to shut down reactors twice in six months due to mechanical failures and electrical shorts. In the first case, an electrical cable that was not up to standards and had been installed in 1986 caused the power shortage leading to the shutdown.

Nonetheless, the majority of the violations were classified as "green" - the lowest level of sanction - which typically do not result in any monetary fine and require only formal written responses.

At the Brunswick Nuclear Power Plant in North Carolina, also operated by Progress Energy, the NRC's report from the time documented confusion and delays in responses among the plant workers after a gas was inadvertently released at the plant. The release should have led workers to activate nearby emergency response shelters and issue warnings to local, state and federal government officials, but the personnel did not know how to activate such alarms.

Eventually plant managers had to step in, and the alarms were only triggered after the federally mandated deadline. Despite the major failure in emergency response, the company was cited with only one potential monetary violation.

A spokesman for Progress Energy said the company has since installed more modern notification systems and increased the number of drills to twice-a-year, up from once every two years.

"We have taken specific actions to address each of the events last year that led to special inspections," the spokesman said in a written statement.

At the Honeywell Specialty Materials plant in Metropolis, Ill., the sole U.S. refinery that processes uranium for use in nuclear power plants, a union lockout has left temporary workers in charge of the facility. The locked-out members of United Steelworkers have erected 42 crosses in front of the Honeywell plant in memory of coworkers who succumbed to cancer in the past decade. Twenty-seven smaller crosses represent colleagues who survived a brush with cancer.

When the plant began hiring replacement employees after the June lockout, the NRC found that management coached candidates on how to properly answer questions on a required examination to work there. According to the NRC, the temporary workers were given answers prior to questioning and were helped during the course of the evaluation process if they became confused.

"The labor force was locked out and the Honeywell facility was trying to qualify as many operators as they could to make sure the plant could operate," NRC inspector Joe Calle said. "The process got overwhelmed, so to speak."

The NRC slapped Honeywell with a violation, and stopped the hiring process. Last fall, the NRC noted in a report that all the temporary workers had been retrained at the plant. The commission expressed assurances that the plant is being safely run.

But the commission has also cited the Metropolis Honeywell plant for a series of other violations since the lockout began, including an uncontrolled furnace ignition resulting when "operating procedures were not followed," according to a letter from the NRC to Rep. Jerry Costello (D-Ill.)

The NRC says it has no definitive proof that temporary workers were at fault, and that the violations were similar to earlier problems that were present when Union workers were working on site. But the locked-out union members pin the troubles on an inexperienced work force that was never fully vetted by the required examinations.

"A lot of people could open up a manual and go by that manual, but in an actual emergency it takes knowledge and experience to be able to handle it correctly and quickly," said a spokesman for the Steelworkers Local 7-669, John Paul Smith.