Microsoft just struck a deal with Constellation Energy to receive energy from the Three Mile Island nuclear site in Pennsylvania. The agreement means that a unit that was shut down five years ago for economic reasons will be restarted.

Constellation said Friday the company has a 20-year deal with Microsoft to restore the Three Mile Island's Unit 1 nuclear power reactor, the site of an infamous nuclear power meltdown.

Microsoft's power needs will restart a reactor at Pennsylvania's Three Mile Island, the site of the worst commercial nuclear power plant accident in U.S. history.