An unappreciated motive for Russia’s invasion of Ukraine is that Kyiv was positioning itself to break from its longtime Russian nuclear suppliers, as the U.S. was encroaching on Russia’s largest nuclear export market.

At the beginning of the conflict, Russian tanks rolled through the Chernobyl site, kicking up dust and increasing radiation levels. Eight days later, the invaders seized the six-unit nuclear power plant in the town of Zaporizhzhya, 700 miles away.

By taking over Chernobyl, Russia gives itself control of the disposal of its spent fuel, which it can store in canisters at the site or ship to a reprocessing facility in Russia. Either way, this represents hundreds of millions of dollars for Rosatom, the Russian state-owned nuclear enterprise.

The shift could displace Holtec, an American designer and maker of dry-storage canister technologies for used nuclear fuel. In 2007 State Specialized Enterprise Chernobyl Nuclear Power Plant authorized Holtec to build a facility to store for 100 years the 22,000 used fuel assemblies from Chernobyl. The project was intended to allow Ukraine to store this fuel safely without shipping it back to Russia for reprocessing. The processing and storage facility was completed in 2020, and Holtec and SSE Chernobyl were loading the canisters to be stored when the war began on Feb. 24.

Further, Ukraine has 15 operating nuclear reactors at four sites, including Zaporizhzhya, that the Russians designed and built. That is the largest number of such plants built by Russians outside their own country. Beginning in 2005, however, the American company Westinghouse emerged as a competitor to the Russian nuclear supplier, Atomstroyexport, owned by Rosatom. At the time of the invasion, Westinghouse supplied fuel to six of the 15 nuclear reactors and could displace the Russians in all of them. The U.S. government had been highly supportive of this effort, and these fuel contracts represented hundreds of millions of dollars in yearly lost sales to Atomstroyexport. By seizing the nuclear plants, Russia is able to retake the market for Ukrainian nuclear fuel.

Most important, Westinghouse, with support from the U.S., was in a position to build nuclear reactors in Ukraine over the next two decades. On Aug. 31, 2021, Energy Secretary Jennifer Granholm and her Ukrainian counterpart, Herman Halushchenko, signed a strategic cooperation agreement to build five nuclear units with a value, according to the World Nuclear Association, of more than $30 billion.

On Nov. 22, Patrick Fragman and Petro Kotin, the CEOs, respectively, of Westinghouse and Energoatom, the Ukrainian state-owned utility, signed a contract to build the first Westinghouse AP1000 nuclear unit in the city of Khmelnitsky, where two Russian-built nuclear units currently operate. The plan was to use the site of a Russian-designed nuclear reactor that had been left about one-third complete in 1990—as well as parts from a canceled American nuclear project in South Carolina. The goal, Mr. Kotin said, was 24 gigawatts of nuclear capability by 2040.

The timing is telling. In November 2021, Ukraine’s leaders signed a deal with Westinghouse to start construction on what they hoped would be at least five nuclear units—the first tranche of a program that could more than double the number of plants in the country, with a potential total value approaching $100 billion. Ukraine clearly intended that Russia receive none of that business.