HARRISBURG, Pa., March 28, 1979 (UPI) -- A cooling system leak, probably the most serious nuclear reactor accident to date, today released radiation and triggered an automatic shutdown of Three Mile island nuclear .power plant, forcing evacuation of the f Blaine Fabian, spokesman for Metropolitan Edison Co., part-owner of the plant, located near Harrisburg, said some radioactive steam escaped and was vented into the atmosphere.
"There was a small off-site release of radiation reported at a possible 10 roentgens per hour, which is very minimal," said Charles Blaisdell, a Civil Defense spokesman.
In Washington, a Nuclear Regulatory Commission spokesman said details were sketchy but the accident appeared to have been a very serious one; knocking out the main reactor cooling. system and forcing the use of the emergency system.
"From what we know now, it would sound like one of the most serious accidents we've had," the spokesman said. But he said it was not the first time a reactor's emergency core cooling system had been activated.
Met-Ed officials said there also was a leak of radiation inside the plant. Fabian said only a minimal staff was present during the shutdown and those reporting for work this morning were kept away from the plant.
Lt. Gov. William Scranton III, who monitors energy matters for the state, said the state Civil Defense had notified communities near the plant but that no evacuation of residents was planned.
Pennsylvania environmental officials confirmed that some radiation escaped into the atmosphere. They said the amount of the release, which they could not measure specifically, was not enough to cause radiation damage through inhalation, although some radiation on the ground could affect milk supplies in about a week.
A Med-Ed spokesman said the 906-megawatt nuclear reactor No.2 automatically shut down at 4 a.m. due to a leak in the secondary cooling system caused by a valve that broke.
"This resulted in some kind of depressurization within the reactor. Then, according to all the emergency and backup systems we have in the plant, the plant shut down," he said. "It was as simple as that."
In Washington, the Union of Concerned Scientists, a nuclear safety interest group, said it received preliminary reports that indicated the plant would have to be shut down for a period of time for decontamination.
The Union said the accident occurred at 4 a.m., plant officials declared a site emergency at 7 a.m., meaning there was some danger at the plant itself, and at 7:45 a.m. called a general emergency because of potential danger outside the area.
The plant is located near Harrisburg International Airport 10 miles southeast of Harrisburg along the Susquehanna River in Dauphin County. A spokesman for the Harrisburg airport said it would remain open.