In short, yes, France was able to build a lot of nuclear in the 80s, but the plans were made in the 70s and, to some extend, reused design and research from the 60s.

Mostly, they benefited from pre-Tchernobyl regulations, and a standardized design that would not be accepted anywhere in the world today if you started from scratch.

After a long hiatus, we sort of managed to build an over engineered post-Fukushima reactor (EPR) in about 20 years, and hopefully learnt lessons so that the next version of the new thing (EPR2) is less of a disaster - but still, you're talking about a decade and a half from presidential ink on paper to electron in the grid if everything goes well - and nuclear is one of those industries where things never go well. Mesmer plan is the exception, not the rule (except if you're Chinese, of course...)