A 40-year-old nuclear plant in Vermont will shut down next year due to the high costs of competing with cheap natural gas, the company said Tuesday.

Entergy Corporation said the Vermont Yankee plant, which employed some 600 people and was licensed to operate until 2032, will be decommissioned after its current fuel cycle ends.

"This was an agonizing decision and an extremely tough call for us," said Leo Denault, Entergy's chairman and chief executive officer.

"We have reluctantly concluded that it is the appropriate action for us to take under the circumstances."

The Louisiana-based Entergy said the move was based on "a number of financial factors," and noted it had poured $400 million dollars into the plant's operations since 2002.

The top reason cited in a company press release was "a natural gas market that has undergone a transformational shift in supply due to the impacts of shale gas, resulting in sustained low natural gas prices and wholesale energy prices."

The company also pointed to "wholesale market design flaws" that lead to "artificially low" energy prices in the region.

The plant's end of operations, or safe shutdown, was set for the fourth quarter of 2014, the company said.

Vermont Yankee is a single unit boiling water reactor that began operating in 1972. Entergy acquired the plant from Vermont Yankee Nuclear Power Corporation in 2002.

Closures of nuclear plants in the United States -- where nuclear energy provides 20 percent of the electricity -- are rare.

Hydraulic fracturing, known as fracking, has led to a massive expansion of natural gas production in the United States.