Over the past 15 years, nuclear utilities in the United States have become better managed, and have improved both efficiency and safety. In the early 1990s, U.S. plants were available to produce electricity only 70% of the time on average. These plants are now producing power more than 90% of the time. More efficient operation has allowed nuclear plants to produce more energy than ever before, adding availability equivalent to 25 new power plants since 1990, without building a single new plant.
Source: U.S. Department of Energy