Among the litany of violations at U.S. nuclear power plants are missing or mishandled nuclear material, inadequate emergency plans, faulty backup power generators and corroded cooling pipes inside a nuclear plant, according to an ABC News review of four years of Nuclear Regulatory Commission safety records.
And perhaps most troubling of all, critics say, the commission has sometimes failed to correct the violations in a timely fashion.
"The Nuclear Regulatory Commission has very good safety regulations but they have very bad enforcement of those regulations," said David Lochbaum, a nuclear scientist with the nonprofit Union of Concerned Scientists.
An industry representative disagrees with the latter characterization, however.
There are 104 U.S. nuclear power facilities, and Anthony Pietrangelo of the Nuclear Energy Institute, an industry association, said, "The plants are very safe. There have been no abnormal occurrences reported by the NRC in their annual report to the federal government from 2005 to 2009."
That's true, but Lochbaum and the Union of Concerned Scientists point to what the NRC calls 14 "near misses" at nuclear plants in 2010, which Pietrangelo called a mischaracterization of those incidents.
"We've got 10 years of very established safety performance," Pietrangelo said. " The indicators that the NRC tracks are at very high safety levels, in some cases record levels of safety. So we stand by our performance.
"They reflect a tough regulator who've got resident inspectors at every site. Each site gets at least 2,000 hours of direct inspection from the NRC every year."
There were 56 serious violations at nuclear power plants from 2007 to 2011, according to the ABC News examination of NRC safety records. At the Dresden Nuclear Power Plant in Illinois, for instance, which is located within 50 miles of the 7 million people who live in and around Chicago, nuclear material went missing in 2007.
The Nuclear Regulatory Commission fined the operator -- Exelon Corp. -- after discovering the facility had failed to "keep complete records showing the inventory [and] disposal of all special nuclear material in its possession."
As a result, two fuel pellets and equipment with nuclear material could not be accounted for.
Exelon did not contest the violation and paid the fine, a company spokesman said. "We took the learnings from that violation with respect to ways we can improve our spent-fuel practices," Marshall Murphy said.
Two years later, federal regulators cited Dresden for allowing unlicensed operators to work with radioactive control rods. The workers allowed three control rods to be moved out of the core. When alarms went off, workers initially ignored them.
Murphy said the company concurred with the NRC's determination. " We have also taken a number of steps to ensure a similar event would not occur at any of our sites and shared the lessons from that with the industry," he said.
"In both violations, neither employees or the public were ever jeopardized, but we take them seriously, we always look to learn from them, and we do that going forward."
Still, Lochbaum of the Union of Concerned Scientists said, "This event is disturbing. In August 1997, the NRC issued information … about a reactivity mismanagement problem at Exelon's Zion nuclear plant," which was retired the following year.