U.S. nuclear power provider Constellation Energy on Friday agreed to buy privately-held natural gas and geothermal company Calpine Corp for $16.4 billion, marking one of the biggest acquisitions in the history of the U.

Constellation Energy Corp., an electricity provider whose stock has doubled over the last year on hopes it will help meet the voracious energy demand created by artificial-intelligence technologies, on Friday reached a $16.

Constellation is buying power natural gas and geothermal power provider Calpine in a cash-and-stock deal valued at approximately $16.4 billion, joining together two of the country’s biggest power companies.