Most nuclear power plants are behemoths, big enough to power a medium-size city. They are also behemoth investments, costing upwards of several billion dollars each to construct. Small wonder then that dozens of small-reactor prototypes are vying for attention in an industry newly energized by nuclear power's advantages as a low-emission alternative to fossil fuels.

"Small reactors can't address all the problems standing in the way of more nuclear investment, but they can address the biggest barriers—the economic ones," says Richard Lester, head of nuclear science and engineering at MIT. Building giant reactors, he points out, isn't the only way to achieve economies of scale; another way is to mass produce inexpensive mini-nukes. If they're designed as modules, a single unit might power a remote town or mine, while a dozen used in tandem could match the output of a traditional nuclear plant. In the developing world, small reactors would place less strain on fragile electrical grids. And the ability to start small and gradually add power modules could appeal to cash-strapped utilities everywhere.