I wouldn't say the lesson was expensive for France, we've enjoyed cheap energy for decades due to this buildup.
The conclusion of this study isn't that France made a costly mistake, it is that it is extremely delusional to forecast ever-increasing efficiency gains when deploying a new technology.
I wouldn't be surprised if the very same lesson was learned by countries planning to go full-renewable.
That's an often repeated falsehood. While there are costs shouldered by the public [1][2], they are similar to what any industry gets. In the following, I compare 2013 costs with the 400TWh produced in 2013:
* Research costs, which are partly funded by private companies and partly funded by the state. These projects currently don't focus on the current infrastructure but on potential new projects. Same as any domain, before a new industry can exist, there's research to be done. With about 784M€ [2] in 2013, that's just under 2€ per MWh. Spending was always within that order of magnitude ever since 1957.
* The surveilance authority is publicly funded, just like any regulatory body. In 2013, it cost about 217M€ [2] which is about 0.5€ per MWh.
So, as you can see, the money spent by the state on nuclear energy in 2013 barely registers compared to the power produced by nuclear plants the same year.
EDF is essentially the state nuclear energy, which has been talks of being renationalized.
> A price cap on energy for French consumers hit EDF profits hard but so did the enforced closure of many of its of nuclear power stations for repairs.
> The losses are the third biggest in French corporate history and the worst for more than 20 years.
Dude, you're talking about taxes, I tell you what ends up on my tax bill.
Now you're telling me that EDF is essentially the state. Sure, but that's pretty much like my own company is essentially me. There are still two separate bank accounts, and clear rules and proper accounting about what goes from one account to the other. That's why I can tell precisely what is on my tax bill and what is on my utilities bill.
My point was that the "EDF is subsidized, a large part of your energy bill is paid by your tax bill" claim is wrong.
Now if you want my opinion about our current (and past) government and how they mismanage EDF and ruin the legacy they received, I can go on for hours. That's unrelated to nuclear, though.
(That, and nuclear weapon ambitions.)