Amazon just made a new nuclear energy investment that could expand the capacity of America's reactor fleet.

Constellation Energy, the country's largest electricity provider, announced a deal with Amazon late on Wednesday to provide the tech giant with power from a Maryland nuclear plant, the Calvert Cliffs Clean Energy Center, for 20 years. Amazon will also help finance a project to expand the nuclear plant's capacity by about 190 megawatts, or enough for nearly 200,000 homes.

The entire refurbishment project of the plant should cost around $3 billion, according to Constellation.

Constellation stock rose 3.3% in after-hours trading.

The financial details weren't released, but these kinds of agreements tend to value electricity at premium prices. Amazon is building data centers in the mid-Atlantic region, but the nuclear plant is not expected to power them directly. Amazon had previously been looking to build data centers directly on the site of the nuclear plant, but it pulled its plans earlier this year after strong community pushback.

Under the deal announced Wednesday, the electricity from the nuclear plant will continue to flow to the larger grid.

The deal is a win for Constellation, whose stock has fallen this year as investors have gotten impatient with the pace of the company's profit growth. Constellation has inked multiple agreements over the past several years to provide power to data centers from its nuclear power plants. But those deals have slowed in 2026, as power providers face regulatory delays and pushback from residents concerned about rising electricity prices.