TerraPower

Scientists have long hoped to revive nuclear power as a commercially viable clean-energy source—ideally without having to build huge, hard-to-maintain power plants. TerraPower, cofounded in 2008 by Bill Gates, hopes to accomplish that mission. The startup has developed smaller, safer, more efficient nuclear reactors—including depleted-uranium-powered “traveling wave” reactors, molten chloride fast reactors, and sodium-cooled Natrium reactors. In June, it broke ground on its first commercial Natrium plant in Kemmerer, Wyo., which should generate power for 250,000 to 400,000 homes once fully operational.