Figure 1. Overnight nuclear plant cost in 2010 dollars as a function of start of construction from \cite{lovering-2016}. The French system never produced plants at should-cost. The cheapest French plants were double the cost of the cheapest American plants in real terms. There is no evidence of a learning curve in the French experience.
I've been getting lots of complimentary comments from the choir on Alex Chalmers' article on the French nuclear build out. The piece is well written, and contains some interesting history I did not know; but Alex puts way too much emphasis on standardization. Voluntary improvements do not increase cost or build times; they reduce them.
The reason for the success of the French program is simple. There was no independent (aka autocratic) regulator. EDF self-regulated until the 1990's. With the development of an independent French regulator after that, French nuclear was doomed.
The French experience is a striking example of what happens when you switch from regulation by an entity that has broad responsibility for providing affordable, reliable electricity to regulation by an autocratic bureaucracy whose job is to prevent a release.