Big Tech is spending big on nuclear to power its AI ambitions. Here's where it's placing its bets.

On Wednesday, Amazon announced it had signed new agreements enabling the development of several small modular reactors — which have a smaller footprint and shorter build times than traditional reactors — to power its data centers.

Energy Northwest, a consortium of public utilities, will construct, own, and operate four reactors across Washington. Amazon is also investing $500 million in X-Energy — a developer of small nuclear reactors and fuel. X-Energy's designs will be used in the Energy Northwest project, the company said.

Amazon is also partnering with utility company Dominion Energy to "explore the development" of a small modular reactor project near the North Anna nuclear power station in Virginia.

Amazon executives said nuclear power offers the cleanest energy to meet the demands of its large data centers.

"One of the fastest ways to address climate change is by transitioning our society to carbon-free energy sources, and nuclear energy is both carbon-free and able to scale—which is why it's an important area of investment for Amazon," Matt Garman, the CEO of Amazon Web Services, said in a press release.

In March, the company also purchased a nuclear-powered data center from Talen Energy.

In September, energy supplier Constellation Energy struck a deal with Microsoft to provide the tech giant with nuclear power for the next two decades by resurrecting part of the Three Mile Island nuclear plant in Pennsylvania.

A spokesperson for Constellation previously told Business Insider that it plans to invest $1.6 billion to reopen one of the Pennsylvania plant's two reactors.

Bobby Hollis, Microsoft's vice president for energy, told Bloomberg that the Three Mile Island reactor will assist Microsoft in meeting its goal of becoming carbon-negative by 2030 and that energy from the site will be used to expand data centers in Pennsylvania and neighboring states.

On Monday, Google said it would purchase nuclear energy from Kairos Power, a California-based company developing small modular reactors. Kairos Power has nuclear projects in New Mexico and Tennessee.

Google said it plans to bring the first small modular reactor in eastern Tennessee online by 2030 and continue with additional deployments through 2035. Overall, the deal will enable up to 500 megawatts of "new 24/7 carbon-free power" for US electricity grids, according to Google.

OpenAI CEO Sam Altman is backing a nuclear reactor startup called Oklo, which also develops small modular reactors.

The company plans to directly sell power to customers through long-term contracts. It went public after merging with Altman's SPAC in May.

Last month, Oklo announced that the Department of Energy had authorized the company to conduct site investigations for its planned reactor at Idaho National Laboratory.

Microsoft, Google, and OpenAI did not respond to a request for comment from Business Insider.