Nuclear reactors currently produce about 11 percent of electricity across the globe. Fueled by uranium, a mined metal that seems to be abundant, they don’t produce the greenhouse gases that have been linked to global warming. So could they generate more power? Opponents point to the risks of nuclear accidents like the one at Chernobyl—and the problem of where to store dangerous radioactive waste. But some innovators are working on new reactor designs, hoping that nuclear power could eventually be price competitive with natural gas and renewable energy sources like wind and solar power.