I must have missed the news about solar and wind being able to flex.
In the UK that would mean 48GW of total capacity. Worst case Nuclear capacity (when plants are offline etc) currently generated by the 5.6GW peak is about 3.8GW (95% of the time nuclear generated more than 3GW, 85% at least 3.7GW)
So that would mean 13 times as much nuclear production in the UK as it currently has to reach 100% use.
Which would generate about 500TWh per year, for a demand of about 250TWh per year, and a peak amount of about 73GW of capacity.
That means the real cost of a nuclear only grid would be twice as much as nuclear currently costs per MWh. Given that nuclear isn't economical today that doesn't really sound sensible.
As both Nuclear and Renewable thus both need "peaker plants" to flex the grid, the "baseload" argument is rather meaningless.
Also nuclear is a non-renewable just a long, nearly impossible to empty one, especially with the longer isotopes of thorium and uranium.
You then supply all power needs above what can be provided by your cheapest power with dispatchable supply. If your base supply is intermittent, that means your dispatchable supply has to be able to supply 100% of peak.