OMAHA, Neb. - The Nebraska nuclear plant that has been idle for nearly three years because of flooding and a series of safety concerns was cleared to restart on Tuesday.

The federal Nuclear Regulatory Commission said the Omaha Public Power District's Fort Calhoun nuclear plant is ready to generate electricity for the first time since April 2011.

NRC inspectors spent more than 23,000 hours reviewing the repairs and improvements before giving the Omaha Public Power District permission to restart the plant that sits across from Iowa on the Missouri River about 20 miles north of Omaha.

"The NRC has concluded that the plant, people and processes are ready to support the safe restart of the Fort Calhoun Station," said Marc Dapas, the regional administrator who approved restarting the plant.

The plant's prolonged shutdown began innocently in April 2011 when routine refuelling was scheduled. But a small electrical fire broke out in June 2011 just before the Missouri River climbed higher and surrounded Fort Calhoun.

The Nuclear Regulatory Commission ordered much tougher oversight at the plant in the fall of 2011 because of those issues and a couple of outstanding regulatory violations like the failure of a key electrical part during a 2010 test. And as the floodwaters receded, the list of things to fix at Fort Calhoun grew.

The fact that Fort Calhoun's troubles started making headlines just months after an earthquake and tsunami crippled a nuclear plant in Japan only added to the scrutiny of the Nebraska plant.

Workers spent more than 2 1/2 years repairing, checking and double-checking more than 450 things around the plant before regulators decided Fort Calhoun is ready.

OPPD spokesman Jeff Hanson said the utility began the restart process on Tuesday after getting permission from regulators, but it may take as long as six days to complete.

"It will be done slowly and deliberately over the course of several days, with several checks along the way," Hanson said.

David Lochbaum, director of the Nuclear Safety Project for the non-profit group Union of Concerned Scientists, said it appears the Omaha Public Power District realized just how far Fort Calhoun had slipped and took the needed steps. But he said it's hard to know how well the plant will perform until it's running.

"The only real proof is to restart it and see if that's the case," Lochbaum said.

OPPD never wavered in its commitment to fix Fort Calhoun because the utility wanted to restore nuclear power to its mix of power sources. Before the shutdown began, Fort Calhoun provided nearly one-third of OPPD's electricity.

And utility officials have said it's important for OPPD to have a significant part of its power come from a plant that doesn't contribute to emissions of carbon dioxide, which is considered a greenhouse gas.

That's why OPPD has been so willing to invest more than $126 million in rehabilitating Fort Calhoun. Ratepayers had to start paying 6.9 per cent more on average last January to fund the repairs but no increase is planned for next year.

One key difference at Fort Calhoun now is that OPPD no longer runs the nuclear plant on a day-to-day basis. The utility hired Exelon Corp. to run the plant because of the Chicago company's experience safely operating 17 nuclear reactors at 10 different power plants.

In addition to overhauling equipment that needed repairs, OPPD and Exelon retrained all the workers to help ensure they will aggressively respond to any future safety concerns. Regulators have said it is clear those lessons are being put into practice because the number of safety reports being submitted has soared.

But for some of Fort Calhoun's critics, nothing will convince them the plant is safe because they're concerned about nuclear power in general and the possibility of the dams upstream of the plant failing.

"The technology is just inherently dangerous," said Mike Ryan with the Clean Nebraska environmental group that has called for Fort Calhoun to be shut down. "I'm more and more convinced now that there's a real danger posed by the upstream dams,"

NRC officials said they would review Fort Calhoun's flood preparations before giving it permission to restart.

Additional NRC inspectors will be on hand at Fort Calhoun to monitor the restart, and the agency will continue watching the plant closely after it starts. And with all the time and money OPPD has invested into the plant, Lochbaum said the utility will work hard to make sure it is operating safely.

"OPPD has used up its get-out-of-jail free cards," Lochbaum said. "If a problem emerges, the NRC will view it more critically and react more forcefully than they would elsewhere."

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Online:

NRC page on Fort Calhoun: http://1.usa.gov/GBq2TF

Omaha Public Power District: http://www.oppd.com

News from © The Associated Press, 2013