> Seasonal, daily, and weekend dips in demand mean you just don’t want that much [nuclear] base load power
One problem is that the US regulatory agency doesn’t like load-following - apparently only one nuclear reactor in the states does it.
It is common in France to do load following i.e. using Nuclear not only for base load but varying load too:
This means that RTE can depend on flexible load following from the nuclear fleet to contribute to regulation in these three respects:
* Primary power regulation for system stability (when frequency varies, power must be automatically adjusted by the turbine).
* Secondary power regulation related to trading contracts.
* Adjusting power in response to demand (decrease from 100% during the day, down to 50% or less during the night, and respond to changes in renewable inputs to the grid, etc.).
PWR plants are very flexible at the beginning of their cycle, with fresh fuel and high reserve reactivity. An EdF reactor can reduce its power from 100% to 30% in 30 minutes. But when the fuel cycle is around 65% through these reactors are less flexible, and they take a rapidly diminishing part in the third, load-following, aspect above. When they are 90% through the fuel cycle, they only take part in frequency regulation, and essentially no power variation is allowed (unless necessary for safety). So at the very end of the cycle, they are run at steady power output and do not regulate or load-follow until the next refueling outage.
NuScale is supposed to be able to vary output too “plant incorporates unique features that enhance its ability to load follow” https://www.researchgate.net/figure/Example-of-NuScale-modul... and https://www.researchgate.net/publication/295114246_Integrati...