Three Mile Island

<span>The&nbsp;<b>Three Mile Island accident</b>&nbsp;was a partial&nbsp;<a href="https://en.wikipedia.org/wiki/Nuclear_meltdown" target="" rel="">nuclear meltdown</a>&nbsp;that occurred on March 28, 1979, in one of the two&nbsp;<a href="https://en.wikipedia.org/wiki/Three_Mile_Island_Nuclear_Generating_Station" target="" rel="">Three Mile Island</a>&nbsp;nuclear reactors in&nbsp;<a href="https://en.wikipedia.org/wiki/Dauphin_County,_Pennsylvania" target="" rel="">Dauphin County, Pennsylvania</a>, United States. It was the worst accident in U.S. commercial nuclear power plant history.&nbsp;The incident was rated a five on the seven-point&nbsp;<a href="https://en.wikipedia.org/wiki/International_Nuclear_Event_Scale" target="" rel="">International Nuclear Event Scale</a>: Accident With Wider Consequences.&nbsp;</span><span>The accident began with failures in the non-nuclear secondary system, followed by a stuck-open&nbsp;<a href="https://en.wikipedia.org/wiki/Pilot-operated_relief_valve" target="" rel="">pilot-operated relief valve</a>&nbsp;in the primary system, which allowed large amounts of&nbsp;<a href="https://en.wikipedia.org/wiki/Nuclear_reactor_coolant" target="" rel="">nuclear reactor coolant</a>&nbsp;to escape. The mechanical failures were compounded by the initial failure of plant operators to recognize the situation as a&nbsp;<a href="https://en.wikipedia.org/wiki/Loss-of-coolant_accident" target="" rel="">loss-of-coolant accident</a>&nbsp;due to inadequate training and&nbsp;<a href="https://en.wikipedia.org/wiki/Human_factors" target="" rel="">human factors</a>, such as&nbsp;<a href="https://en.wikipedia.org/wiki/Human-computer_interaction" target="" rel="">human-computer interaction</a>&nbsp;design oversights relating to ambiguous control room indicators in the power plant's&nbsp;<a href="https://en.wikipedia.org/wiki/User_interface" target="" rel="" title="Link: https://en.wikipedia.org/wiki/User_interface">user interface</a>. In particular, a hidden indicator light led to an operator manually overriding the automatic emergency cooling system of the reactor because the operator mistakenly believed that there was too much coolant water present in the reactor and causing the steam pressure release.<a href="https://en.wikipedia.org/wiki/Three_Mile_Island_accident#cite_note-MTM-5" target="" rel="">[5]</a></span><span>The accident crystallized&nbsp;<a href="https://en.wikipedia.org/wiki/Anti-nuclear" target="" rel="">anti-nuclear</a>&nbsp;safety concerns among activists and the general public, resulted in new regulations for the nuclear industry, and has been cited as a contributor to the decline of a new reactor construction program that was already underway in the 1970s.<a href="https://en.wikipedia.org/wiki/Three_Mile_Island_accident#cite_note-6" target="" rel="">[6]</a>&nbsp;The partial meltdown resulted in the release of unknown amounts of&nbsp;<a href="https://en.wikipedia.org/wiki/Radioactive" target="" rel="">radioactive</a>&nbsp;gases and radioactive&nbsp;<a href="https://en.wikipedia.org/wiki/Iodine-131" target="" rel="">iodine</a>&nbsp;into the environment. Dire predictions were made by&nbsp;<a href="https://en.wikipedia.org/wiki/Anti-nuclear_movement" target="" rel="">anti-nuclear movement</a>&nbsp;activists;&nbsp;however&nbsp;<a href="https://en.wikipedia.org/wiki/Epidemiology" target="" rel="" title="Link: https://en.wikipedia.org/wiki/Epidemiology">epidemiological</a>&nbsp;studies analyzing the&nbsp;<a href="https://en.wikipedia.org/wiki/List_of_countries_by_cancer_rate" target="" rel="" title="Link: https://en.wikipedia.org/wiki/List_of_countries_by_cancer_rate">rate of cancer</a>&nbsp;in and around the area since the accident, determined there was a small&nbsp;<a href="https://en.wikipedia.org/wiki/Statistical_significance" target="" rel="" title="Link: https://en.wikipedia.org/wiki/Statistical_significance">statistically non-significant</a>&nbsp;increase in the rate and thus no&nbsp;<a href="https://en.wikipedia.org/wiki/Causal" target="" rel="" title="Link: https://en.wikipedia.org/wiki/Causal">causal</a>&nbsp;connection linking the accident with these cancers can be made.&nbsp;Cleanup started in August 1979, and officially ended in December 1993, with a total cleanup cost of about $1&nbsp;billion.</span>