The control room for the Unit 1 reactor at the Three Mile Island nuclear plant.

Here’s an overview of key moments in the life of the Three Mile Island nuclear plant, which parent company Exelon said Wednesday will be shut down by Sept. 30, 2019.

May 1968: Construction of TMI begins

Sept. 1974: Unit 1 begins commercial operations

Dec. 1978: Unit 2 begins commercial operations

March 28, 1979: Partial meltdown of Unit 2 reactor

April 1, 1979: President Jimmy Carter arrived to tour the crippled plant

April 4, 1979: Governor Dick Thornburgh announced that the "threat of any immediate catastrophe" had ended; Unit 2 never restarts

1985: Unit 1 resumes commercial operations

2009: Federal regulators grant Unit 1 a 20-year extension allowing operations until 2034, and two huge steam generators on self-propelled transport cross Lancaster County at a rate of 2 to 3 miles per hour as part of a 20-day journey to TMI

2015: TMI failed to sell its electricity at a key energy auction for the first of what would be four straight years

May 2017: Citing heavy losses, Exelon said it would close TMI in Sept. 2019 without significant changes

Jan. 2018: Federal Energy Regulatory Commission rejected Trump administration proposal to bail out struggling nuclear and coal plants

March 2019: Legislation calling for electric ratepayers to prop up nuclear power in Pennsylvania is introduced in Pennsylvania House, followed by similar legislation in Pennsylvania Senate

May 8, 2019: Exelon announces that TMI will close on or by Sept. 30, 2019

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