Nuclear power provides 20% of the US's electricity from 103 nuclear plants. California gets power from two reactors at Diablo Canyon and two at San Onofre, as well as a share of three reactors in Arizona. Worldwide there are 440 reactors in 31 countries producing 16% of global electricity. Issues with nuclear power include high costs, waste disposal, and safety concerns from past incidents. New designs aim to address these issues and expand nuclear power's role in a sustainable energy future.