Or, you know, one could just take the cost of the French fleet and inflation-adjust it? Technology wasn’t that different when they were built. And building scores of reactors has tremendous efficiencies of scale.
It is no longer legal to build the kinds of Gen 2 plants France built their fleet out of, so I don't see how inflation-adjusting that cost would be more accurate than looking at the current market cost.
As an example, today plants are required to not suffer meltdowns if primary power is lost to cooling systems. Many similar sets of rules (see EU Nuclear Safety Directives from 2009 and 2014, for example), add up to much more plant complexity, which increases capex.
Now the thing is, loss of coolant is rather bad for both coal, gas and oil power plants as well. They may break, pollute water, explode...
And the cessation of generation is about as problematic.
They have not been redesigned for alternate coolants, unlike new nuclear power plants.
As an example, today plants are required to not suffer meltdowns if primary power is lost to cooling systems. Many similar sets of rules (see EU Nuclear Safety Directives from 2009 and 2014, for example), add up to much more plant complexity, which increases capex.