For the foreseeable future, building enough nuclear for peak capacity is exceedingly expensive.

> None of the power plants ever do a "fast cold start"

Somewhere in each grid you will have “black start” capacity contracts, dunno if nuclear can fills this role (or if grids exclude nukes for one reason or another).

Plenty of peaker plants built with the intention of running double digit hours per year and therefore the tradeoff supports being largely “off” in between those calls. Batteries might fill that gap.