Watts Bar #2 was the last one in the US to come online started construction in 1972 came online in 2016... These are the sorts of timelines that make these things hard sells to modern boardrooms and investment strategies.
Stopped in 1985, resumed in 2007
After the restart of construction it ended up being considerably more expensive than promised.
Some contributing factors: new regulations requiring partial redesign; global financial crisis; being Gen II and therefore highly impacted by brain drain
I think they mean it's been 40 years since a plant was built.