What happen in three mile island?

Answer 1

There was a cooling system malfunction at TMI-2, which resulted in a loss of coolant accident (LOCA) that damaged the nuclear core. Compounding the event was an apparent failure to trust instinct when some of the water level gauges malfunctioned. The biggest problem, however, was the lack of an adequate emergency plan, resulting in partial public panic and an unnecessary partial evacuation. Another problem was that the design of the radiation instrumentation did not anticipate the actual levels, making the actual levels uncertain.

Post accident analysis reveals that about 43,000 curies of 85Kr were released, and that about 20 curies of 131I were released. Due to atmospheric dispersal, however, no significant impact was experienced by the public. For further discussion of off-site impact, please see the Related Link below.

Two major changes occurred in policy following the incident. First, intermediate and high range radiation monitoring equipment was mandated, so that no conceivable evolution could place the instrumentation off-scale high. In fact, some of this equipment is so high range that, if they really were pegged off-scale high, you would be safer on the moon without a spacesuit. Suffice to say, its not going to happen. Second, and more importantly, was the requirement for a fully integrated emergency plan and drills to exercise that plan. The issue here is full transparency and trust.