Timeline of the accident at Three Mile Island
By The Patriot-News
CHRISTINE BAKER, The Patriot-News
Unit 2 has been in service for about three months. Unit 1 is shut down for refueling.
A minor malfunction in the non-nuclear part of Unit 2 occurs, triggering a series of automated responses in the reactor's coolant system, including the opening of a relief valve on top of the pressurizer to relieve pressure.
The relief valve fails to close automatically when the pressure drops. Control room operators misread the situation and mistakenly believe coolant is being pumped into the system. Meanwhile, the valve remains open for 2 1/4 hours as precious reactor coolant spews out. An automated emergency cooling system also is turned off.
By now, high radiation levels exist in several areas of the plant, and evidence indicates as much as two-thirds of the 12-foot-high core has stood uncovered. A partial meltdown of the fuel bundles occurs.
Shortly before 7 a.m., a site emergency is declared -- a requirement when some event threatens "an uncontrolled release of radioactivity to the immediate environment."
State and local authorities, nearby counties and the state police are alerted.
A general emergency is declared.
WKBO, a Harrisburg music station, is the first to broadcast the news of a problem at Three Mile Island. The station's reporter was told the problem presented no danger to the public.
State police close Route 441 to traffic near TMI. An hour later, the U.S. Department of Energy begins its first helicopter flight to monitor radiation levels.
A noise, described as "a thud" is heard in the Unit 2 control room. The "thud" was the sound of a hydrogen explosion inside the containment building. At the time, however, the noise is dismissed as the slamming of a ventilation damper.
News media flood into the area throughout the afternoon.
Photo by Robert Del Tredici
George Stauffer with niece Tammy Pfeifer, Middletown, June 6, 1979. Stauffer lived through the accident without experiencing alarm or dread. "The only damage that occurred was from all those reporters who trampled on everybody's flowers. ... As for me, I put my faith in the man upstairs." Images are from the book "The People of Three Mile Island" (Sierra Club Books, SF 1980).
An initial alarm has given way to a wait-and-see attitude. The Pennsylvania Emergency Management Agency is told periodically throughout the day that the situation is improving.
Lt. Gov. William P. Scranton III tours the Unit 2 control room and auxiliary building in the afternoon, wearing a radiation suit and a respirator during part of the inspection. Members of the local congressional delegation are briefed by officials of the Nuclear Regulatory Commission and Metropolitan Edison, which owned TMI at the time.
Gov. Dick Thornburgh holds a news conference at which an NRC official says the danger for people off of Three Mile Island is over.
NRC officials are told that the core damage is far worse than expected.
The governor's office is told of the new information by the NRC, which indicates that a greater possibility of radiation releases exists.
Bureaucratic snafus, poor communication among officials and overeager news reporting later are determined to be responsible for reports issued this day that there had been high radiation releases.
The NRC recommends Thornburgh order an evacuation, but NRC Chairman Joseph Hendrie soon assures Thornburgh that no evacuation is needed. However, Hendrie suggests that all people within five miles downwind of the plant be urged to stay indoors.
The Associated Press/2004
Former Gov. Dick Thornburgh
Around 10 a.m.
Thornburgh issues an advisory that all people within 10 miles of the plant stay inside.
Thornburgh, receiving conflicting information, advises pregnant women and preschool children to leave the region within five miles of TMI.
Schools in the area close after the advisory. Penn State Harrisburg calls off classes for a week. Many residents decide to leave the area.
Thornburgh asks President Carter to dispatch a single expert upon whom the governor could rely for advice.
Police are placed on alert and residents are told to stay indoors with windows closed and ventilating systems off. Local emergency management agency officials go on the radio to tell people what they should take with them if an evacuation is ordered.
Residents become more nervous as they try to make phone calls but hear no dial tones; lines are overloaded.
Harold Denton, the NRC troubleshooter dispatched by Carter, arrives at Three Mile Island. By now, NRC officials have realized that a hydrogen bubble has formed in the Unit 2 reactor.
Officials say there is a "remote" possibility that the bubble could force down vital cooling water, exposing the reactor core and causing a meltdown.
Hendrie, the NRC chairman, says at a news briefing that a precautionary evacuation of residents within a 20-mile radius might be necessary if engineers are to attempt to force the bubble out of the reactor. Later, Carter announces plans to visit Three Mile Island the following day .
The Associated Press reports, based on information from several NRC sources, that the hydrogen bubble might become a potentially explosive mixture within days.
Denton assures reporters at a late evening news conference that there "is no imminent catastrophic event foreseeable." By this evening, one-quarter of the area's 950,000 residents have packed suitcases, withdrawn savings from banks and fled the area.
Rusty Kennedy, The Associated Press/1979
Wearing protective boots, then-President Jimmy Carter, center right, accompanied by Dr. Harold Denton, then director of the U.S. Nuclear Agency, left, and then Pennsylvania Gov. Dick Thornburg, left-rear, tour the control room of the Three Mile Island nuclear plant in Middletown, Pa. in this April 1, 1979 file photo, four days after the nuclear accident.
Carter tours TMI and addresses residents in the Middletown community building.
Roman Catholic priests grant general absolution during Sunday Mass. Granting of such absolution is usually restricted to war or other circumstances when it might be impossible for people to make confessions to priests.
Area hospitals accept only emergency admissions, to clear beds in the event an evacuation is required.
Denton announces that the hydrogen bubble has shrunk dramatically.
Denton announces that the hydrogen bubble has been eliminated. Later studies show the bubble had probably been eliminated two days earlier.
The Federal Reserve announces that it has dispatched large sums of cash to area banks that had seen a large number of people withdraw cash in preparation for leaving the area.
Thornburgh, appearing on the NBC "Today" show, announces that the "threat of any immediate catastrophe is over."
The precautionary evacuation advisory for pregnant woman and preschoolers is lifted.