Three Mile Island
THREE MILE ISLAND
The most serious nuclear reactor accident to date in the United States occurred at 4 A.M. on March 28, 1979, at the Three Mile Island nuclear power plant outside Middletown, Pennsylvania. Operator errors in dealing with a pump that had shut down caused the Unit 2 pressurized-water reactor to lose coolant and overheat. The temperature of the reactor core then rose to the point at which some of the zirconium-alloy fuel cladding failed, fuel itself partially melted, and cladding reacted with steam to produce bubbles of vapor and hydrogen, which then escaped into the reactor building, along with fission products from the reactor core. As a result of the failure to close a backup valve that could be operated manually, coolant was not restored to the reactor core until more than six hours after the accident, by which time enough hydrogen had accumulated in the building to pose the treat of a low-level explosion. The building had been designed to seal automatically in the event of a pressure rise, but no rise occurred, and four hours were allowed to elapse before the building was sealed, during which time radioactive gases escaped into the atmosphere.
Within three hours after the first sign of trouble, elevated radiation levels were detected by monitors in the reactor auxiliary building. A site emergency was declared, and officials enlisted the aid of local, state, and federal emergency personnel. The presence of a large hydrogen bubble in the reactor vessel prompted widespread fear that the reactor might explode, a concern that experts failed to allay although they knew it to be a misapprehension. Adding to the fear, dosimeter readings made in a helicopter three hundred feet above the auxiliary building's ventilation stack were misinterpreted by officials to signify elevated ground levels of radiation, prompting the governor of Pennsylvania to recommend the evacuation of all pregnant women and preschool children residing within five miles of the plant, who then complied.
Although large amounts of radiation were released, the resulting exposure of the public was relatively slight, resulting mainly from xenon-133
ARTHUR C. UPTON
Baum, A.; Gatchel, R.; and Schaeffer, M. (1983). "Emotional, Behavioral, and Psychological Effects of Chronic Stress at Three Mile Island." Journal of Consulting and Clinical Psychology 51:565–572.
Kemeny, J.G. (1979). The President's Commission on the Accident at Three Mile Island. New York: Pergamon Press.
Moss, T. H., and Sills, D. L., eds. (1981). "The Three Mile Island Nuclear Accident: Lessons and Implications." In Annals of the New York Academy of Sciences 365. New York: New York Academy of Sciences.