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Omaha • The Omaha Public Power District voted Thursday to shutter the Fort Calhoun Nuclear Station, which is the nation's smallest nuclear power plant.

The board decided it was in the best financial interest of the utility and its customers to close the plant by the end of this year, the utility said in a statement after the vote. The plant sits on the Missouri River across from Iowa and is about 15 miles north of Omaha.

"This was a difficult vote and one we did not take lightly," said Mick Mines, the board's chairman. "The industry is changing, and it is imperative that we make strategic decisions to better position the district in the future for all our 365,000 customer-owners."

Among the factors cited in the decision to close the plant was the low price of natural gas, which makes it a cheaper way to generate electricity, and a federal energy plan that doesn't offer carbon-free generation credit for existing nuclear plants.

The board also noted the recent early retirement of several other U.S. nuclear power stations.

The utility said that as a result of the closure, it doesn't expect a general rate increase in the next five years, through 2021.

The move was expected. OPPD president and CEO Tim Burke told the board last month that operating the plant was no longer financially sustainable. That was based on a third-party analysis that found that shutting the plant would save the district $735 million to $994 million over the next 20 years. Utility officials estimated last year that the plant was costing about $250 million a year to operate.

The power district has amassed about $388 million for the decommissioning effort.

Once closed, a nuclear plant must undergo a decommissioning process to remove or decontaminate materials and equipment that have been exposed to radioactivity. The Nuclear Regulatory Commission requires decommissioning to be completed within 60 years of a plant's closing.

Cleaning up the site after its closure is estimated to cost $1.2 billion, the utility said.