70% of reactors are over 25 years old, 23% are over 35 years old, so within 10 to 20 years about a third will have to be decommissioned, far more than the 63 under construction. Some are bound to fail as they age, making the future of nuclear power even less certain.
The U.S. depends on nuclear power plants built with designs from the 1950s that have known flaws.
Worse yet, the U.S. has 23 reactors with the same design as those in Fukushima Japan that melted down after the 2011 earthquake and tsunami.
In both old and more recent plants, the components face a daily load of high temperatures, pressures, vibration and bombarding neutrons, which can render thick steel walls so brittle that cracks form at welds and joints (Biello).
Biello, D. Feb 7, 2015. Sorry State: U.S.’s Nuclear Reactor Fleet Dwindles. Scientific American.
Number of operating reactors by age (as of June 26, 2007). Age is determined by first grid connection. Source: IAEA power reactor information system