BANGKOK — China has built a land-based prototype nuclear reactor for a large surface warship, in the clearest sign yet Beijing is advancing toward producing its first nuclear-powered aircraft carrier, according to a new analysis of satellite imagery and Chinese government documents provided to The Associated Press.

China’s navy is already the world’s largest numerically, and it has been rapidly modernizing. Adding nuclear-powered carriers to its fleet would be a major step in realizing its ambitions for a true “blue-water” force capable of operating in seas far from China in a growing global challenge to the United States.

“Nuclear-powered carriers would place China in the exclusive ranks of first-class naval powers, a group currently limited to the United States and France,” said Tong Zhao, a senior fellow at the Carnegie Endowment for International Peace in Washington, D.C. “For China’s leadership, such a development would symbolize national prestige, fueling domestic nationalism and elevating the country’s global image as a leading power.”

Researchers at the Middlebury Institute of International Studies in California said they made the finding while investigating a mountain site outside the city of Leshan in the southwest Chinese province of Sichuan, where they suspected China was building a reactor to produce plutonium or tritium for weapons.

Instead they concluded that China was building a prototype reactor for a large warship. The project at Leshan is dubbed the Longwei, or Dragon Might, Project and is also referred to as the Nuclear Power Development Project in documents.

Neither China’s Defense Ministry nor Foreign Affairs Ministry responded to requests for comment.

Satellite images and public documents helped identify likely carrier project

There have long been rumors that China is planning to build a nuclear-powered aircraft carrier, but the research by the Middlebury team is the first to confirm that China is working on a nuclear-powered propulsion system for a carrier-sized surface warship.

“The reactor prototype at Leshan is the first solid evidence that China is, in fact, developing a nuclear-powered aircraft carrier,” said Jeffrey Lewis, a professor at Middlebury and one of the researchers on the project. “Operating a nuclear-powered aircraft carrier is an exclusive club, one that China looks set to join.”

Drawing on satellite images and public documents including project tenders, personnel files, environmental impact studies — and even a citizen’s complaint about noisy construction and excessive dust — they concluded a prototype reactor for naval propulsion was being built in the mountains of Mucheng township, some 70 miles (112 kilometers) southwest of Sichuan’s provincial capital Chengdu.

The reactor, which procurement documents indicate will soon be operational, is housed in a new facility built at the site known as Base 909, which houses six other reactors that are operational, decommissioned or under construction, according to the analysis. The site is under the control of the Nuclear Power Institute of China, a subsidiary of the China National Nuclear Corp., which is tasked with reactor engineering research and testing.

Documents indicating that China’s 701 Institute, formally known as China Ship Research and Design Center, which is responsible for aircraft carrier development, procured reactor equipment “intended for installation on a large surface warship” under the Nuclear Power Development Project as well as the project’s “national defense designation” helped lead to the conclusion the sizable reactor is a prototype for a next-generation aircraft carrier.

Satellite mages from 2020 to 2023 have shown the demolition of homes and the construction of water intake infrastructure connected to the reactor site. Contracts for steam generators and turbine pumps indicate the project involves a pressurized water reactor with a secondary circuit — a profile that is consistent with naval propulsion reactors, the researchers say.