Three Mile Island nuclear plant in Pennsylvania could prove highly consequential — for the green-energy transition and much else besides. Constellation will invest $1.6 billion to restart one reactor at the plant — known globally as the site of an infamous meltdown more than four decades ago — while Microsoft will agree to buy 20 years’ worth of power for its data operations.

The owner of the shuttered Three Mile Island nuclear power plant said Friday that it plans to restart the reactor under a 20-year agreement that calls for tech giant Microsoft to buy the power to supply its data centers with carbon-free energy.