For about 10 percent of electricity in the United States, it’s fuel from dismantled nuclear bombs, including Russian ones.

“It’s a great, easy source” of fuel, said Marina V. Alekseyenkova, an analyst at Renaissance Capital and an expert in the Russian nuclear industry that has profited from the arrangement since the end of the cold war.

But if more diluted weapons-grade uranium isn’t secured soon, the pipeline could run dry, with ramifications for consumers, as well as some American utilities and their Russian suppliers.