LACEY TOWNSHIP, N.J. >> A nuclear power plant long considered to be the oldest in America shut down Monday, the victim of its age and inability to compete with newer, cheaper gas-fired power plants.

The Oyster Creek Nuclear Generating Station in New Jersey went offline at noon Eastern time today, powering down without incident for the final time after nearly a half-century of operation.

Oyster Creek and the Nine Mile Point Nuclear Generating Station near Oswego, New York both went into operation in December 1969. The U.S. Nuclear Regulatory Commission had long listed both facilities as going online Dec. 1, 1969 — a date the agency acknowledged on Monday is incorrect.

Nine Mile Point says it went into commercial operation on Dec. 14, 1969; Oyster Creek says it did so on Dec. 23, 1969. But Oyster Creek’s license was granted on April 10, 1969, the company said, about four months before one was given to Nine Mile Point, according to a 1970 document from the U.S. Atomic Energy Commission, a precursor agency to the NRC.

Both plants, which are now owned by Exelon, say they have for decades considered Oyster Creek to be the older of the two, an assessment widely shared in the nuclear industry.

“It’s a somber day,” said Tim Moore, the plant’s vice president. “We watched emotionally as our reactor shut down for the very last time.”

Nine Mile is now the oldest of the nation’s 98 remaining nuclear power plants, said Neil Sheehan, a spokesman for the U.S. Nuclear Regulatory Commission.

The plant in Lacey Township near the Jersey shore has dealt with corrosion and leaks during its time in service, but its owner, Chicago-based Exelon Corp., says the plant has always been safe.

Oyster Creek became a victim of its advanced age and the rapidly changing economics of power generation. In 2010, Exelon reached an agreement with the administration of former New Jersey Gov. Chris Christie, a Republican, under which the plant would shut down within 10 years in return for not being required to build costly cooling towers to meet upgraded environmental standards.

That deal, along with a glut of cheap natural gas that makes it more economical to run power plants on gas than nuclear fuel, helped seal its fate.

“We’re seeing the economic conditions regarding nuclear power plants erode,” said Dave Tillman, an Exelon spokesman.

Despite the fact that nuclear power emits virtually no planet-warming greenhouse gases, many environmentalists had long sought the shutdown of Oyster Creek over the years, citing corrosion that dangerously thinned its reactor vessel, and the leak of radioactive tritium into groundwater on the plant site.

Jeff Tittel, director of the New Jersey Sierra Club, called Oyster Creek “a disaster waiting to happen. By closing early, it will help protect both the environment and public safety. We’ve been fighting this plant for more than 15 years and this closure is long overdue.”

But the plant also has been the mainstay of the local economy in Lacey Township, a small town in the Pinelands near Barnegat Bay where fishing and recreation draw residents. The power plant is by far the town’s largest employer and source of property taxes; the township’s coat of arms has a nuclear isotope in it.

Nick Juliano, the town’s Republican mayor, is concerned about the impact of the plant’s shutdown on the local economy and property tax base. But he is heartened that 300 of the 400 workers currently employed at the plant will remain there as fuel rods are removed and placed into secure storage. He also is optimistic that the sprawling site can be redeveloped.

“We’re going to miss that plant,” he said. “I wish they’d stay. The impact on the homes, the real estate, there’s a lot of things we’re dealing with.”

Jupiter, Florida-based Holtec International plans to buy Oyster Creek next year and speed up the decommissioning of the plant if necessary approvals are granted.