If your transmission line to your nuclear power station trips, you need reserve capacity elsewhere to serve the load.
Gas and coal generation all need storage to run reliably.
If you are going to be an armchair power system designer and you want to ‘gross up’ the cost of capacity and storage into the cost of renewable generation, then be consistent.
Solar cannot act as the backup to a nuclear power plant. Whereas a nuclear power plant can (and does) act as the backup to solar.
I'm grossing up to make the point that after about 60-70% solar penetration, the circle cannot be squared without massive investment either in batteries or in distribution, a fact which seems to never quite fully make it into cost comparisons between nuclear and solar such as those being made in this thread.
But AFAIK you can't just turn nuclear plants on and off again based on demand like you can do with gas. So it's not really a backup.
But batteries are not the ideal storage technology for all storage use cases. It turns out that e-fuels like hydrogen are much, MUCH better for some cases, like seasonal leveling, even though the round trip efficiency isn't great.
It will likely be the case that a 100% RE grid ends up being considerably cheaper than a nuclear powered grid.
Nuclear backing up solar is a completely stupid idea, btw. The economics don't work at all.