MOSCOW — When the Soviet Union introduced its Alfa class submarine — at the time, the world’s fastest — the subs were the bane of American sailors. Now, the reactors that powered those submarines are being marketed as the next innovation in green power.

Environmentalists say the technology is outdated and potentially dangerous, and marketing it as green energy is an abuse of nuclear power’s good green name.

The Russians are not alone in pushing the idea that the next generation of nuclear reactors should have more in common with the small power plants on submarines than the sprawling installations of today.

The kinds of marine reactors the Russians are promoting, though, also happen to create a byproduct — used fuel — that no one knows how to handle. Right now, that spent fuel is being stored at naval yards in the Russian Arctic.