Three Mile Island On March 28, 1979, a series of mechanical, electrical, and human failures led to what has been described as the worst nuclear power plant accident in United States history. News of the accident shook the country and its effects were deeply felt by those who lived in the shadow of Three Mile Island's great concrete towers. The accident began around 4 a.m. on March 28, 1979, when there was a breakdown in the non-nuclear secondary section of the plant. The main feedwater pumps stopped working, due to a mechanical or electrical failure preventing the steam generators from discharging heat. First the turbine, then the reactor stops automatically. Then the pressure in the primary system (the nuclear part of the plant) began to increase. To prevent this pressure from becoming excessive, the pressurizer relief valve opened. The valve should have closed when the pressure dropped a certain amount, but it didn't. The signals available to the operator did not indicate that the valve was still open. As a result, the stuck open valve caused a continued drop in pressure in the system. Meanwhile, another problem emerged in another part of the factory. The emergency feed water system, a backup to the main feed water, was tested 42 hours before the accident. As part of the test, a valve is closed and then reopened at the end of the test. But this time, due to administrative or human error, the valve was not reopened. This error prevented the operation of the emergency water supply system. The valve was discovered closed approximately eight minutes after the accident began. After reopening, the emergency water supply system began to function properly, allowing cooling water...... middle of paper ... to draw water from the core. In conclusion, today, waves of white steam escape from the double hourglass-shaped cooling towers of TMI's only functional unit, which cost $7 million to build. Operators say it is a model of efficiency and safety. But under a deal expected to close this summer, the plant will be sold for $100 million, or one-seventh of its book value. Three Mile Island was the worst nuclear disaster in the United States and because of this accident, many nuclear power plants were forced to close or upgrade their facilities.Bibliography: Works CitedBlashfield, Jean F., et al. Global warming. Children's Press, 1991 "Global Warming" CD-ROM Microsoft Encarta, Microsoft Corporation, 1997 ed. "EPA Global Warming", http://www.epa.gov/globalwarming/ (November 27, 1999) "Index of /gwcc", http://www.gcrio.org/gwcc/ (November 27). 1999)