Number of operational nuclear reactors worldwide 1954-2021. By the end of 2021, there were 437 operational nuclear reactors worldwide. That was a decrease of five operational nuclear reactors compared to the previous year. In 2021, the construction of ten new nuclear power plants began globally. In 1959 there were just 11 operable reactors, and within 30 years the number had shot up to 420. Since 1989, reactor numbers have remained relatively stable, peaking at 450 in 2018.