Earlier quoted context omitted.
Balancing a nationwide power grid is very complex. Some energy sources can be started and stopped instantly, but are limited - water. Others are plentiful, but unpredictable - wind. Others are predictable, but take a long time to start and stop - gas, coal(several hours), nuclear(1 day to start, fast to stop, but very expensive). A balanced grid will need all of them, will need them in quantities which can cover faul…
Nuclear power plants can vary their output faster than most people think, see https://www.oecd-nea.org/upload/docs/application/pdf/2021-12... ... most of the modern light water nuclear reactors are capable (by design) to operate in a load following mode, i.e. to change their power level once or twice per day in the range of 100% to 50% (or even lower) of the rated power, with a ramp rate of up to 5% (or even more) of…
You could just keep it spinning nonstop without a load I suppose, but for anything but nuclear it's not gonna be economical.