> The obvious counterexample is Chernobyl,

You mean the obsolete design that is not used even in old reactors, not to say of modern designs?

Quote:

--- start quote ---

The minimum requirements for the manoeuvrability capabilities of modern reactors are defined by the utilities requirements that are based on the requirements of the grid operators. For example, according to the current version of the European Utilities Requirements (EUR) the NPP must at least be capable of daily load cycling operation between 50% and 100 % of its rated power Pr, with a rate of change of electric output of 3-5% of Pr per minute.

--- end quote ---

> The situation is going to look drastically different for a renewables-first grid, where additional sources are needed for at most a few hours a day, for a few months per year.

Ah, to live in these mythical times...