OMAHA, Neb. (AP) — A letter from the chief executive of Omaha Public Power District says the utility will permanently shut down its nuclear plant at Fort Calhoun this fall.

That comes from correspondence it obtained from OPPD President and CEO Tim Burke to the U.S. Nuclear Regulatory Commission. The letter, dated Thursday, says the Fort Calhoun plant will be shuttered Oct. 24.

The utility’s board voted in June to permanently close the plant.

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 closure.

Cleaning up the site after its closure is estimated to cost more than $1 billion.