FILE – This Feb. 28, 2017, file photo shows Indian Point Energy Center in Buchanan, N.Y. (AP Photo/Seth Wenig, File)

ALBANY, N.Y. (AP) — With the push of a red button, one of the two operating reactors at an aging nuclear plant serving millions of people in the New York City area will shut down Thursday night as federal regulators consider the owner’s proposal to sell it to a company that plans to demolish it.

The Unit 2 reactor at the Indian Point Energy Center along the Hudson River will close for good Thursday, and Unit 3 will close in April 2021, as part of a deal reached in January 2017 between Entergy Corp., the state of New York and the environmental group Riverkeeper.

The plant generated a quarter of the electricity used in New York City and suburban Westchester County, where the plant is located, in 2017. But the corporation that runs the state’s electrical grid concluded the closure won’t impair its ability to keep the lights on because new natural gas plants and efficiency measures are picking up the slack.

Operators will press a button that inserts control rods into the reactor adjacent to the nuclear fuel, Entergy spokesman Jerry Nappi said Tuesday. The control rods absorb neutrons, which stops the fission that creates the energy.

Staffing will be reduced from about 800 to 300 workers about 30 days after Unit 3 shuts down next year, Nappi said.

Gov. Andrew Cuomo, a Democrat, had long sought the shutdown, saying the plant 24 miles north of Manhattan in Buchanan posed too great a risk to millions of people who live and work nearby.

Riverkeeper noted Hudson River fish kills, soil and water contamination, recurrent emergency shutdowns and vulnerability to terrorist attacks. Entergy cited low natural gas prices and increased operating costs as key factors in its decision to close Indian Point.

A year ago, Entergy announced a deal to sell the 240-acre plant to the New Jersey-based decommissioning firm Holtec International, which has submitted a dismantling plan to the Nuclear Regulatory Commission. The plant is to be demolished by the end of 2033 at a projected cost of $2.3 billion.

At an online public information session last week, NRC representatives said the commission is reviewing Holtec’s financial and technical qualifications, as well as public comments, before approving the license transfer.

According to the NRC, Indian Point will join 13 other nuclear power plants across the United States that have begun the decadeslong process of decommissioning, which dismantles a facility to the point that it no longer presents a radioactive danger.

Entergy said in a statement that it is committed to continued operation of the five nuclear power plants in its utility business in Louisiana, Arkansas and Mississippi. It shut down its Pilgrim plant in Massachusetts last year and plans to shut down its Palisades plant in Michigan in 2022, both for decommissioning by Holtec.

Under the decommissioning process, spent fuel rod assemblies are initially placed in water where they are cooled for at least two years. Then the spent fuel is transferred into steel and concrete cylinders that stay at the site unless or until a national nuclear waste storage facility is created.

Opponents of the Indian Point shutdown note that it does not spew air emissions and will be replaced largely by fossil fuel sources that contribute to climate change.

But a recent study by the Oakland, California-based Physicians, Scientists and Engineers for Healthy Energy found that renewable energy goals required by the state will make a sustained increase in natural gas generation unnecessary.

By Mary Esch