THREE MILE ISLAND DISASTER By SRUTHI SRINIVAS
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AT A GLANCE Location three mile island, dauphin country, Pennsylvania, US Date: 4:00am ,28, march, 1979 Type nuclear accident "Cause : meltdown of core
INTRODUCTION It occurred on march,28,1978 in reactor number 2 of three mile island nuclear generating plant Itwas the most significant accident in US commercial nuclear power plant history The incident was rated a five on the seven point international nuclear event scale(INES).
THREE MILE ISLAND NUCLEAR GENERATING STATION (TMI) It is a nuclear power plant located on three mile island in Pennsylvania on the Susquehanna river. The plant was originally built by general public utilities cooperation, later renamed GPU incorporated has two separated units,TM 1-1 and TM 1-2. The construction of TMI unit-1 is started on may,18,1968 and unit-2 is started on vember,1,1969
INCIDENT The accident began when the plant experienced a failure in the secondary, non- nuclear section of the plant (one of two reactors on the site) A mechanical or electric failure prevented the main feed-water pumps from sending to the steam generators, that remove heat from the reactor core. Water pumps that helped to cool the radioactive fuel in the reactor core malfunctioned set off an unlikely series of events that led to a partial meltdown at the Unit 2 reactor.
Operators didn't realize the reactor was experiencing a loss of coolant and further starved the reactor core of water flow and caused it to overheat. In order to control that pressure, the pilot-operated relief valve opened. It was locat d at the top of the pressurizer. The valve should have closed when the pressure fell to proper levels, but it became stuck open.
Instruments in the control room, however, indicated to the plant staff that the valve was closed. As a result, the plant staff was unaware that cooling water in the form of steam was pouring out of the stuck-open valve. As alarms rang and warning lights flashed, the operators did not realize that the plant was experiencing a loss-of-coolant accident nuclear fuel began to melt through its metal container and about half the reactor core melted.
Trace amounts of radioactive gasses escaped into the surrounding community. The melting fuel created a large hydrogen bubble inside the unit that officials worried might cause an explosion. Three days later when experts determined the hydrogen bubble could not burn or explode.
CAUSES A combination of personnel error, design deficiencies, and component failures caused the TMI accident of the auxiliary pumps that fed water into the steam generators. Malfunction of water feeder pump Closing the valves was the primary reason for relatively minor incident escalated into a meltdowrn Instruments available to plant staff provided inadequate or misleading information
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