Three Mile IslandOn 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 U.S. history. News of the accident shook the nation, and its effects were keenly felt by those who lived in the shadow of Three Mile Island's great concrete towers. The accident began around 4:00 am on March 28, 1979, when a failure occurred in the secondary, non-nuclear section of the plant. The main feedwater pumps stopped working, due to a mechanical or electrical failure that prevented the steam generators from removing heat. First the turbine, then the reactor automatically shut down. Then the pressure in the primary system (the nuclear part of the plant) began to increase. To prevent the pressure from becoming excessive, the pressurizer safety valve opened. The valve was supposed to close when the pressure dropped by a certain amount, but it didn't. The signals available to the operator did not demonstrate that the valve was still open. As a result, the stuck valve caused a continuous decrease in pressure in the system. Meanwhile, another problem occurred in another part of the plant. The emergency supply system, a backup to the main supply water, was tested 42 hours before the accident. As part of the test, a valve is closed and then reopened once the test is complete. But this time, due to administrative or human error, the valve was not reopened. This error prevented the emergency power system from functioning. The valve was discovered closed approximately eight minutes after the accident. After reopening, the emergency water supply system began to function properly, allowing the cooling water... in the middle of the paper... to draw water from the core. In conclusion, today waves of white vapor from the double hourglass... cooling towers in the shape of TMI's only functioning unit, which cost $7 million to build. Operators say it is a model of efficiency and safety. But in a deal to be signed this summer, the plant will be sold for $100 million, one-seventh of its book value. Three Mile Island was the worst nuclear disaster in the United States, and because of that accident many nuclear power plants were forced to close or upgrade their facilities. Bibliography: Works Cited Blashfield, 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 to /gwcc", http://www.gcrio.org/gwcc/ (27 Nov. 1999)