[toast0]

From wikipedia, the most recent nuclear plant to enter operation in the US is Watts Bar reactor 2. It entered operation in 2016, while being under construction for a total of 17 years; 8 years between 1973 and 1985, then 9 more between 2007 and 2016.

The Vogtle plant reactor 3 and 4 project started in 2006, construction started in 2013, and planned operation is 2021; but these things are often delayed. And that was at an existing site. 20 years may be pessimistic, but not unduly so, based on recent experience.