"There were opportunities to find this sooner," Lochbaum said. "It's embarrassing to find something like this, but not unheard of."
The Nuclear Regulatory Commission sent Omaha Public Power District a notice in 1985 to replace Teflon as insulation in the building housing Fort Calhoun's reactor. The utility subsequently replaced it on wires that it considered at critical risk but left some in places it did not consider a safety concern.
Commission spokeswoman Lara Uselding said her agency's oversight process relies on nuclear plant operators identifying and fixing problems while commission inspectors scrutinize that work. This system, she said, has not been successful at the Omaha plant.
"Historically at Fort Calhoun, that has not gone well and that is why they are currently under increased oversight," Uselding said.
Acknowledging the deterioration of performance at Fort Calhoun before the shutdown, the utility signed a 20-year deal with Exelon Corp. last fall to operate the nuclear plant.
Lochbaum said OPPD will have to fix the structural problem and convince the commission that there are no other surprises lingering at Fort Calhoun. He thinks that's possible.
"So far it looks like they're still on the path to restart," Lochbaum said.
Utility officials said part of why they believe it's worth repairing Fort Calhoun is that the cost of nuclear fuel is stable in comparison to coal and natural gas, and that it produces no greenhouse gases.
"It's a reliable source of electricity that's carbon-free. That becomes more valuable going forward," OPPD spokesman Jeff Hanson said.
But it will be difficult to convince some that Fort Calhoun is safe and a good investment.
The Sierra Club of Iowa has asked the commission to revoke Fort Calhoun's operating license because of its history of safety violations. Mike Ryan, with the environmental group Clean Nebraska, said he would rather see the nuclear plant closed.
"The attitude of the NRC is always making sure it's safe before restart. What if you can't make it safe?" he said.
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NRC page on Fort Calhoun: http://1.usa.gov/GBq2TF
Omaha Public Power District: http://www.oppd.com