From a windswept corner of Hokkaido, Japan Steel Works Ltd. controls the fate of the global nuclear-energy renaissance.

There stands the only plant in the world, a survivor of Allied bombing in World War II, capable of producing the central part of a nuclear reactor's containment vessel in a single piece, reducing the risk of a radiation leak.

Utilities that won't need the equipment for years are making $100 million down payments now on components Japan Steel makes from 600-ton ingots.