When they’re not inventing sentient chatbots, tech giants have a new obsession: nuclear power. Last week, Alphabet’s Google and Amazon.com both announced investments innew kinds of reactors. 

It’s the latest sign that nuclear energy is making a comeback, some 50 years since the technology was last considered a growth industry. The trend had already lifted the stocks of companies that own reactors, including Vistra and Constellation Energy.

But the Google and Amazon deals signal a new phase where companies could actually build new nuclear reactors. As a result, a separate group of stocks has begun to rise—companies that are designing, building, and fueling novel kinds of nuclear generators—and they could keep gaining. That includes Nuscale Power, Oklo, BWX Technologies, GE Vernova, Lightbridge, and Centrus Energy, all of which rose last week.

Nuclear energy stocks gained again in morning trading Monday. Lightbridge rose 35%; NANO Nuclear Energy rose 17%; Oklo rose 16%; NuScale Power rose 5%.

On Wednesday, Amazon said it would finance the construction of several small nuclear reactors in Washington state and invest in Maryland start-up X-energy, which will build the reactors. The news came after Alphabet’s Google announced on Monday that it had made a deal with privately held Kairos Power, a California-based developer of small nuclear reactors, to support the development and construction of several reactors. Financial terms weren’t released, but Kairos expects to get the first reactor up and running by 2030 and potentially build several more by 2035. 

The tech giants are looking for ways to secure power for their data centers, which are consuming more electricity as artificial-intelligence usage grows. The firms say they want to reduce their carbon footprints to slow global warming, and executives think nuclear fits the bill. Nuclear plants don’t emit carbon and operate continuously, unlike solar and wind.