Fifty years ago today, the nuclear age dawned in southwestern Pennsylvania.

At 4:30 a.m. Dec. 2, 1957, the first commercial nuclear reactor in the United States, built on a seven-acre site along the Ohio River in Shippingport, Beaver County, gained full power, or, as the scientists like to say, achieved "initial criticality."

It would take until Dec. 18 to plug the electricity produced by splitting atoms into the region's power grid. But for nearly 25 years thereafter, the plant lit up area homes and furthered atomic research.

Jointly developed by the Department of Energy and Duquesne Light Co., the plant was part of President Dwight D. Eisenhower's "Atoms for Peace" program

"It was the world's first large-scale nuclear-powered electric-generating system, and also a scientific and research station," said Scott Waitlevertch, a spokesman for FirstEnergy's Beaver Valley nuclear power station, which operates adjacent to the old Shippingport facility. "There were several core designs over the years that went in, and that allowed them to really look into the technology."

Adapted from a reactor originally intended for use on an aircraft carrier, the original Shippingport pressurized-water reactor, designed by Westinghouse Electric Corp., cost $72.5 million and ran on 93 percent enriched uranium. Construction of the facility, which was mostly underground for safety and security reasons, was overseen by Adm. Hyman Rickover, the "father of the modern nuclear Navy."

The reactor was tiny by today's standards, producing 68 megawatts of electricity, enough to light about 68,000 homes. The nuclear fission the reactor produced heated water to produce steam, which drove the turbines that produced electricity.

By comparison, FirstEnergy's Unit 1 and Unit 2 nuclear reactors produce about 1,779 megawatts of power.

The last reactor used by the facility, from 1977 to 1982, was an experimental breeder reactor, Mr. Waitlevertch said, that produced not only electricity but also more nuclear fuel, thus the "breeder" component of the reactor.

"Shippingport was like a submarine on land," said Richard Hecht, 58, who started as a test engineer at the old Shippingport plant 34 years ago. He's now FirstEnergy's engineering training coordinator, but misses the old reactor and the small, tight-knit family of employees there.

"I have fond memories of that place. They ran a tight ship. Admiral Rickover made sure of that, but we knew everyone who worked there," said Mr. Hecht. He even met his future wife, a clerk in the radiation-protection department, there.

The Shippingport plant was closed in 1982. Its reactor vessel was shipped to the Hanford low-level radioactive waste disposal facility in Richland, Wash., via the Mississippi River and the Panama Canal. The riverfront site was cleaned at a cost of $98 million, in 1985 dollars, and released for unrestricted use in November 1987.

Although government officials said at the time it was safe enough to be used as a children's playground, the site, as a result of the terrorist attacks of Sept. 11, 2001, is surrounded by a security fence and used mainly by Canada geese.

"It's sad to look at that field and a shame we lost some of our history when the reactor was shipped out and the buildings taken down," said Darleen Kopp, 64, who worked at the Shippingport reactor as a nurse for six years and now performs the same duties for FirstEnergy.

Still around is Jim Russell, who helped build the Shippingport reactor as a 17-year-old laborer, operated it as a supervisor and worked on its shutdown and decommissioning.

"I was hired on Sept. 25, 1957, and one of the first jobs I had was to pick up the spent welding rods around the omega seal that connected the head to the reactor vessel," said Mr. Russell, 68. "So that's how I can say I worked on the construction."

Asked about his memories of the morning when the reactor was fired up and attained full power, he paused, then laughed.

"I was there," he said, "but I was 17 years old and interested in girls. It was just a job for me. I was mystified by it."

The Shippingport anniversary occurs at a time when the federal licenses for the two nuclear reactors operated by FirstEnergy Nuclear Operating Co. on land adjacent to the site of the original reactor are up for renewal.

Earlier this month, the Akron, Ohio-based electric company announced its Beaver Valley Power Station had met the Nuclear Regulatory Commission's preliminary requirements to extend the permit for its Unit 1 reactor until 2036 and its Unit 2 reactor until 2047. A decision on the permits is not expected until the last half of 2009.