A number of safety lapses at U.S. nuclear power plants last year occurred because the plants' owners and often the Nuclear Regulatory Commission failed to properly address problems, the Union of Concerned Scientists said Friday in a report.

The nonprofit, nonpartisan organization has been scrutinizing nuclear plant safety for more than four decades.

The report cites NRC inspections conducted in response to safety equipment and security problems at 12 plants. None of the 14 "near-misses" that led to inspections during the year resulted in harm to plant workers or the public, but their frequency is high, the group said.

"It's evident the NRC is capable of being an effective watchdog," said Dave Lochbaum, director of UCS's Nuclear Safety Project and author of the report. "But too often the agency does not live up to its potential, and we are still finding significant problems at nuclear plants that could trigger a serious accident."

"Many of the near-misses last year involved problems that were festering for years, if not decades," he added. "That means that the plant owners' testing and inspection regime is broken. Nothing is going to change unless the NRC requires plant owners to fix it."

Based on a survey of agency staff carried out last fall, Lochbaum said the NRC's "safety culture" is compromised. Fewer than half the agency's workers believe the agency takes safety culture surveys seriously, it said.

"It is laudable that the NRC wants plant owners to establish and maintain positive safety culture at their nuclear plants," Lochbaum said. "It is laughable that the NRC's own safety culture is so wanting."

Lochbaum said the NRC often does not enforce its own rules on reactor coolant leaks. He cited a 28-day leak last summer of reactor coolant at the Palisades plant in Michigan.

The NRC could have fined the owner $3.92 million but instead fined it nothing, the UCS report said.

In a statement, the NRC said the term "near misses" implies "that these incidents almost became a Fukushima. In fact, the NRC's oversight of the nation's commercial reactors is designed to identify and resolve potential problems long before they can threaten public health and safety. So instead of saying 'the sky almost fell,' we view these incidents as examples of the system working. And even UCS acknowledges in the report that there was no harm to public health and safety by any of these events."