Just five countries account for 71 percent of the world's nuclear electricity generation capacity, and the United States sits at the top of that list, according to Energy Information Administration data. The concentration reflects decades of reactor construction in a handful of nations and frames where global nuclear output is anchored.

The United States operates the largest reactor fleet, with its plants supplying close to a fifth of national electricity. The country's capacity has stayed broadly stable in recent years, with output supported by high utilization rather than a rapid build-out of new units, though that pattern is beginning to shift as new projects advance.

Behind the leading group, dozens of countries operate smaller fleets, and more than 40 nations have announced plans to add nuclear capacity. The data highlights how a small number of established nuclear countries continue to dominate installed capacity even as interest broadens worldwide.

For the US grid, the figures point to both a strength and a question. The existing fleet provides a large, reliable base of low-emission generation, but much of it was built decades ago. Sustaining the country's leading position will depend on license renewals for aging reactors and on bringing new large and small reactors online as electricity demand rises.

Source: U.S. Energy Information Administration - https://www.eia.gov/todayinenergy/detail.php?id=65904