Lacey Township, N.J. ? A consumer and environmental advocacy group urged the Obama administration to freeze construction of new nuclear reactors and halt re-licensing of the oldest of the nation’s 104 plants until safety lessons from the Japanese nuclear crisis can be absorbed.

The U.S. Public Interest Research Group issued a report Tuesday citing a history of safety problems at nuclear reactors in the United States.

It cited problems stretching back two decades at nuclear plants in Ohio, North Carolina, South Carolina, Kansas, New York, New Jersey and Vermont, including four considered “significant precursors” to damage to the reactor’s core. There have been four such incidents in the U.S. since 1990, and 17 since 1979.

“Nuclear power is a high-stakes gamble that threatens public safety,” the group wrote. Comparing nuclear reactors and slot machines, the report said the odds of getting one “7” on any slots play are fairly good, the chances of getting two are smaller, and the odds of getting three are slim, even though it happens from time to time.

“Nuclear power plants are like Vegas slot machines — but with costly and damaging accidents, rather than big payouts, the uncommon yet inevitable result,” the report read. “This report reviews a series of incidents over the past 20 years at U.S. nuclear reactors in which one or even two unlucky 7s fell into place.

“In each of these cases, Americans were spared the kind of nuclear disaster on our soil that has contaminated food and drinking water, threatened the health of workers, and sparked widespread and disruptive evacuations in Japan,” the report read. “But each of them represented a window of opportunity that might, under different circumstances, have led to disaster.”

It claims U.S. plants are not immune to natural disasters, human error or other dangers that could cause a catastrophe similar to the one unfolding at Japan’s tsunami-damaged Fukushima Daiichi power plant.

Neil Sheehan, a spokesman for the U.S. Nuclear Regulatory Commission, said the report “is essentially a compendium of already reported and widely known issues with which the NRC is quite familiar.”

He said the agency required a series of safety improvements at U.S. nuclear power plants in the 1980s and 1990s, plus additional upgrades after the Sept. 11, 2001, terror attacks.

Earlier this month, just after the Japanese crisis erupted, the NRC decided to conduct short- and long-term safety reviews of all U.S. nuclear plants “to check on whether the Japanese reactor events hold any implications for them,” he said.

A quick-look review should be completed within 30 days.

“Subsequent to that, the NRC will continue to look for lessons learned from the events involving the Japanese plants,” Sheehan said, adding a task force has been appointed to carry out a long-term review.

The report listed a 2002 incident at the Davis-Besse Nuclear Generating Station in Ohio as perhaps the most dangerous in the U.S. since the partial meltdown at Pennsylvania’s Three Mile Island in 1979.

Workers discovered that boric acid leaking from a cracked nozzle had eroded away six inches of carbon steel on the Davis-Besse reactor vessel head, leaving less than half an inch of steel to contain the reactor’s highly pressurized steam. Rupture of the vessel head could have led to loss of coolant and damage to the plant’s control rods, leading to a rapid overheating of the reactor core and possible release of radiation.

The report also cited the following cases:

• In 1996, critical systems at the Catawba Nuclear Station in South Carolina were without power for several hours when the plant lost outside electrical power at the same time one of its emergency generators was down for maintenance.
• In 1994, workers at the Wolf Creek nuclear power plant in Kansas accidentally allowed 9,200 gallons of coolant to drain from the reactor core.
• In 1991, valves and drain lines in an emergency shutdown system at the Shearon Harris nuclear power plant in North Carolina failed.

The report also cited 27 U.S. nuclear plants that have leaked radioactive tritium, including the Salem plant in Lower Alloways Creek, N.J., and the Oyster Creek Nuclear Generating Station in Lacey Township, N.J., a problem that was discovered just days after the NRC granted the plant a new 20-year license.

Other tritium leaks were found at the Braidwood Nuclear Generating Station in Illinois, at the Indian Point Energy Center in New York, and in ground water near the Vermont Yankee plant, even though the plant’s owner maintains it had no underground pipes capable of leaking radioactive material.

Oyster Creek, the nation’s oldest nuclear power plant, will be shut down in 2019, 10 years earlier than expected, under a deal with New Jersey environmental regulators that will enable the plant’s owners, Chicago-based Exelon Corp., to avoid having to build costly cooling towers that would drastically reduce the number of fish and small marine creatures killed by the plant’s operation.