Constellation Energy has made a key investment in its effort to restart the Three Mile Island nuclear reactor in Pennsylvania, purchasing a $100 million main power transformer. The transformer is the largest piece of equipment needed to bring the plant, which has been inactive since 2019, back online.

The plant, now renamed the Crane Clean Energy Complex, is best known for the 1979 nuclear accident that affected Unit 2. Unit 1, which Constellation aims to restart, was shut down for economic reasons but is expected to produce 835 megawatts of power when operational again in 2028.

Last month, Constellation signed a $1.6 million power agreement with Microsoft to supply electricity to offset the tech giant's data center consumption. The deal is part of a broader trend where energy companies are partnering with the technology sector to meet the rising electricity demand driven by artificial intelligence and cloud computing.

Restarting the plant will require several other investments, including upgrades to the reactor's turbine, generator, and cooling systems. U.S. regulators have noted that no modern nuclear plant has been restarted after a full shutdown, adding both technical and regulatory challenges to the process.