Three Mile Island

Although one of the reactors did suffered a severe core meltdown, the consequences outside the plant remained minimal, the containment building remained intact and held almost all of the accidents radioactive material. ---------------->

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As a result, the staff took a series of steps, based on incorrect assumptions, that made there situation even worse. ------------->

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On March 28, 1979, the Three Mile Island nuclear power plant experienced a cooling malfunction that caused the temperature of the coolant to rise.

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Their actions starved the reactor of coolant, causing it to overheat.

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Without the proper water flow, the nuclear fuel rods overheated to the point at which they began to melt (a partial core meltdown).

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All instruments in the control room, however, indicated that the valve was closed. As a result the staff did not know that coolant was leaking out of the reactor. ---------------->

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As more and more coolant escaped, other instruments provided inadequate information.

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In order to relieve the pressure in the reactor a pilot-operated relief valve (PORV) opened, once the pressure fell it should have closed, but remained stuck open.

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This caused the reactor to automatically shutdown, which in turn caused the pressure in the reactor to increase. ------------>

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