Omaha Public Power District workers found a flaw this week in one of more than 50 heaters that help maintain the temperature of the water used to generate steam at its Fort Calhoun Nuclear Station, but the utility said Friday that the plant remains safe and shut down.
OPPD found the problem Monday and reported it to the Nuclear Regulatory Commission two days later, after determining the problem could be significant. It was discovered while workers were replacing a faulty heater and following up on a report of a problem with similar heaters last year at a British nuclear power plant.
The nuclear power plant, about 20 miles north of Omaha, has been shut down since April 2011. The utility is working with NRC officials to thoroughly inspect the plant and make sure it is safe before restarting.
OPPD officials said the system with the flawed heater operates only when the plant is running.
NRC officials did not immediately respond to messages left Friday.
OPPD is working to address regulators' concerns about past safety problems.
The violations found at Fort Calhoun include a small electrical fire last June, the failure of a key electrical part during a 2010 test and deficiencies in flood planning that were discovered a year before last summer's extended flooding along the Missouri River.
Fort Calhoun was surrounded by floodwaters for much of last summer, though workers were able to keep water out of critical areas of the plant.
OPPD's chief nuclear officer, Dave Bannister, said the utility began inspecting the heaters on Fort Calhoun's pressurizer last year after a British utility found a crack in one of its heaters. Such heaters are part of Fort Calhoun's reactor cooling system.
No problems were found initially, but Bannister said two of the heaters at Fort Calhoun had stopped working before the plant shut down last spring, so officials decided to replace those faulty units.
One heater was replaced in November, but the heater with the problem was stuck and couldn't be removed until this week, when experts with the right gear could visit Fort Calhoun.
Bannister said workers found a small crack in the steel shield that surrounds the heater, but no coolant leak.
“We never saw any leakage on this. We caught it early,” Bannister said.
OPPD tentatively plans to restart Fort Calhoun in late September, Bannister said Friday. The schedule could change if any new problems are found during this summer's inspections.
“Before we restart the plant, we'll walk down and test every piece of equipment,” Bannister said.
The timing of the restart means OPPD will again have to purchase electricity from other sources to meet peak summer demand, but officials don't expect rate increases this year because of that.
Last year OPPD spent about $32 million to buy electricity from other sources while Fort Calhoun was closed.
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