Raleigh, N.C. — Progress Energy's nuclear generating plants experienced the most near-mishaps last year of any utility in the U.S., according to a report released Thursday.

The report from the Union of Concerned Scientists comes as Japanese officials try to stabilize nuclear reactors damaged last week by a massive earthquake and tsunami.

The UCS, an environmental advocacy and watchdog group, said that Progress Energy and the U.S. Nuclear Regulatory Commission need to exercise more oversight to improve the performance of the Raleigh-based utility's plants.

"While the company may simply have had an unlucky year, corporate-wide approaches to safety may have contributed to this poor performance," the report said. "When conditions trigger special inspections at more than one plant with the same owner, the NRC should formally evaluate whether corporate policies and practices contributed to the shortcomings."

Progress Energy spokesman Mike Hughes defended the company's safety record.

"(Nuclear plants) have been demonstrated as safe for more than 40 years. We've been operating plants since 1971 in the Carolinas, and those plants have been very, very safe," Hughes said.

He did acknowledge, however, that the company's nuclear plants had their share of problems last year.

"2010 was clearly not a banner year in those terms, and we certainly didn't perform to the level we know our regulators expect (and) that we expect of ourselves," he said.

The UCS noted Progress Energy plants in Southport and in South Carolina and Florida accounted for four of 14 incidents nationwide that led to special inspections by the NRC.

Two of the incidents occurred at the H.B. Robinson plant in Florence, S.C., last March and October. The UCS compared the incidents, an electrical fire and an equipment failure, to those that led to the near-meltdown at Three Mile Island in Pennsylvania in 1979.

At the Brunswick plant in Southport, workers couldn't respond quickly to an alarm last June, the report state. At the Crystal River plant in Crystal River, Fla., workers caused $500 million in damage to a reactor's concrete containment building when installing a new generator, according to the report.

"(Inspectors) provided input into what we needed to respond to, what we needed to address, what we needed to improve on," Hughes said. "We've taken steps and continue to take steps to address all of them."

The Shearon Harris nuclear plant in southwest Wake County was the only Progress Energy plant not named in the UCS report.

Charlotte-based Duke Energy, which is in the process of acquiring Progress Energy, was cited in the report for a security problem at its Catawba plant in Rock Hill, S.C.

UCS noted that none of last year's safety problems caused harm to plant employees or the public, but they expressed concern that regulators appeared to tolerate unresolved safety issues in several cases.