The United States operated 94 commercial nuclear reactors at 54 plant sites across 28 states as of early 2026, with combined net summer generating capacity of 98,441 megawatts, according to Nuclear Energy Institute statistics.

The fleet's average annual capacity factor reached 91 percent in 2025, higher than any other generation category. The 2024 figure stood near 92.3 percent. Capacity factors have held close to 90 percent since the turn of the century, a level reached only after more than a decade of sustained operational improvement across the fleet during the 1990s.

The practical meaning of that number is availability. A 91 percent capacity factor indicates the fleet produced 91 percent of the electricity it would have generated running continuously at full rated output for the entire year, with the remaining time accounted for by refueling outages and planned maintenance.

The comparison against other sources is where the figure carries weight for grid planners. Combined-cycle natural gas plants and utility-scale wind and solar operate at materially lower capacity factors, meaning a nameplate megawatt of nuclear capacity delivers substantially more annual energy than a nameplate megawatt of most alternatives.

Nuclear generation supplied approximately 18 percent of utility-scale United States electricity in 2025, with more recent estimates placing the share near 19 percent.

Source: Nuclear Energy Institute - https://www.nei.org/resources/statistics/us-nuclear-generating-statistics