I should have said "when not sunny", not "at night". Point being - without vastly improved and expanded energy storage, you cannot have a reliable grid powered by renewables. But with nuclear, you can ditch fossil fuels.

Nuclear becomes exponentially more expensive the more you add to the grid and thus the lower it’s capacity factor becomes. France was exporting a lot of nuclear power and importing non nuclear and still fell down to 70% cf when the US was at 90%. One way of looking at that is a .9/.7 - 1 = 30% increase in cost per kWh overall. However compared to 90% for 35% the next 35% cost 60% more per kWh. And aiming for 90% would be even more expensive.

If we want a zero carbon grid nuclear simply isn’t viable on it’s own, it needs massive energy storage or peaking power just like wind and solar.

Yeah, I was thinking more in terms of nuclear base capacity (humming along at ~constant output) and renewable for peaks. Still need vastly more and better storage for that, but not as much as exclusively renewable.

Also, not being in this field, I may have misunderstood you or confused the terminology.