To simplify without oversimplifying: Modern nuclear plants can change between 30% and 100% of nameplate capacity within half an hour, and that's how they operate in France for instance. While coal plants might rev up from 75% to 100% in a twice-daily shift change, but are clearly not set up to run at minimal loads.

https://en.wikipedia.org/wiki/Load-following_power_plant#Nuc...