The problem is that Nuclear may not be economical if it is only used when both solar and wind run out. Nuclear has large fixed costs. And almost zero marginal costs. So the average costs -- what needs to be charged in order to avoid bankruptcy, increase as you use it less.

That means every solar panel you add makes the nuclear power a bit more expensive. And that incentivizes adding more solar. Up until you drive the nuclear out of business, and then suddenly you don't have reliable power anymore.

Then you are faced with a situation of

a) only having nuclear power which can provide for all of your needs, in which case adding solar is an unnecessary expense

b) only having solar+wind and an unreliable grid, which means you need to add batteries to cover solar+wind. And the price of those batteries may be more than the price of the nuclear plant.

c) having nuclear and solar both, with enough subsidies given to the nuclear plant to keep it in business so that the total solution is more costly than just going with nuclear.

So yeah, there really is a tension between nuclear and solar.

This is not the situation, however, with solar and coal. Because coal plants are damn cheap, and they have higher marginal costs. Thus solar can coexist with coal or with gas much better than with nuclear.

Therefore the economics is such that as people promote solar the result is a decrease in nuclear and an increase in coal and gas.