That article neglects that the plants built by the end of the program were not the same as the plants built in the beginning. Within each "pallier", a speedup can clearly be observed. Likewise, costs can hardly be compared if you don't look at the same models.
I have no idea how a speedup appears to you. On the graph it is quite clear that, with time (and therefore experience), the average amount of time needed to build one is raising.
That's 2-3rds of the builds showing a speedup. The results are even more striking if you calculate the correlation between start date and build time for any 2 reactors of the same model.
Yes, I considered the long-term experience gain (columns, not lines: from 65 to 151 and from 60 to 104).
The first nuclear plants were theoretically the most difficult to build as the local industry was less adjusted to building such things, especially specific components.
As those reactor 'models' were very similar (there is no quantum leap) pertinent experience (processes, tooling...) accumulated.
However there was no reduction of 'intensity' (investments, amount of simultaneous building projects, foreseeable projects...) as all this was encompassed by a huge national programme (the 'Plan Messmer').
Therefore it seems that both min and max time to completion should diminish with time.
> Yes, I considered the long-term experience gain (columns, not lines: from 65 to 151 and from 60 to 104). [...] As those reactor 'models' were very similar [...]
They're not the same buildings. A N4 is much larger than a CP0, uses different technologies, has more safety features, produces much more power, etc.
To compare with another tech topic, that's like expecting SpaceX to design or build their spaceship faster or cheaper than they designed their falcon. That's unlikely, even though falcon knowledge definitely benefited the design of their new craft.
Not exactly the same but same generation, architecture and design (Westinghouse), slightly (not fundamentally) enhanced. Stating that new features add such a large amount of work (relatively to the total amount) that it compensates for the knowledge gained thanks to previous projects is debatable.
Between the oldest (CP0) and newest (N4) aren't the key differences limited to a same machine and command room shared (CP0) or not (N4) between reactors, scale (CP0's nominal power being lower), and details related to fuel rods and pipes? In which way are they dissimilar to the point of absorbing the effect of gained knowledge and adding such delays?
Even the shiny new EPR is a mere enhancement of the core design dating back ~1970.
Sorry, I don't know enough about SpaceX to have an opinion.
> Even the shiny new EPR is a mere enhancement of the core design dating back ~1970.
If you push this logic to its end, even a tesla car is a mere enhancement of the electric cars produced in 1900. There is no breaking change like wings, the ability to teleport or supersonic speed.
If you look in details what changed between CP0's and N4's though, there's quite some change [1]: N4's have a double containment enclosure while CPO's have a single one, the vessel contains 400m3 vs. 270m3 and weights almost 50% more, sustains 15 mor bars and 15 more °Cs, and it produces almost 60% more power.
Enough progress for Westinghouse to value Framatome's experience to the point that they became a partner, stopped paying license fees and earned the right to export their design[2].
The N4 double containment is a mainly quantitative change, as are all the other changes you mentioned: the very architecture remains the same, as do the associated exploitation processes.
Those modifications were big enough to justify seeing the N4 as a "new design" because the French worked hard to master this design, and since 1981 (Nuclear Technical Cooperation Agreement, NTCA) Westinghouse & the French formally exchanged know-how. Moreover Westinghouse didn't work on the N4 and it escaped the Westinghouse license (which expired in 1992). However the very design isn't disruptive.
As for this approach efficiency the note #17 seems pertinent.
[1]: https://fr.wikipedia.org/wiki/Centrale_nucl%C3%A9aire_en_Fra...