Three Mile Island Accident Study

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Three Mile Island Accident Study

1. Introduction
Based on the NRC (1), the Three Mile Island nuclear power plant is a commercial nuclear plant where has two nuclear reactors (TMI-1 and TMI-2). General Public Utilities Corporation built the power plant and Metropolitan Edison Company ran and managed the plant. TMI-1 and TMI-2 reactors were pressurized water reactors; and their generated power were 802 MWe and 906 MWe respectively. TMI-2 had an accident on March 28, 1979, particularly, the reactor was melted and radioactivity was released to the outside of plant. Fortunately, there was no detectable effects on workers, public and surrounding environment due to radioactive release. However, the direct economic losses cause by this accident
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The mechanical failure got the pilot-operated relief valve stuck, meanwhile the relief valve status showed in the control room was closed. Consequently, the coolant flowed out of reactor core through valve; and the temperature of reactor core was rising.
Because the information provided by the system was inadequate, so that operators did not know the water level. As a result, they assumed that the water level was high in the reactor core and did not realize that the reactor was experiencing losing cooling water. The coolant pumps was switched off to protect themselves from the acute vibration. Furthermore, operators cut down the supply of emergency cooling to the reactor core. These series of action did not relieve the hazard, but made reactor into the dangerous situation. As a result of these actions, the reactor core suffered with overheating. Moreover, there was a crack on the zirconium cladding that was a cover for the nuclear fuel pellets. It led to that the nuclear fuel pellets starting to melt and flow out from the crack. Fortunately, the building where place the TMI-2 did not have any break, so it prevented workers and surrounding from strong and direct radioactivity.

3 hours later than the feed water pumps stopping working, the operators just realized that the reactor core had melted because of abnormal core temperature. Even though some operators did not believe the temperature reported by the control system. After 15 hours 50 minutes from the fault
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