That's not how it works. I don't know the actual numbers, but what if peak load is 50% higher than average load? You need quite a lot of battery storage to make that work, especially if the peak load lasts longer than a few minutes (it usually does).
And that's true even assuming instant capacity adaptation. It's just not efficient to keep nuclear power at a capacity lower than their peak capacity.
> I don't know the actual numbers, but what if peak load is 50% higher than average load
You'd know if you read the link I provided.
Nuclear plants in Germany had no issues scaling up and down between 400-600MW and 1200-1400MW per reactor per day.
Now, with renewables you do have this issue. Because due to their intermittent nature you're required to both overbuild them and provide enough grid-scale storage to last for hours.
> It's just not efficient to keep nuclear power at a capacity lower than their peak capacity.
For some politically-motivated definition of efficient. Additional costs to running nuclear plants in load following mode are immaterial.
How is it immaterial to build twice as many nuclear power plants as necessary instead of using energy storage? You'd have to believe battery storage is way more expensive than an idle nuclear plant. But that's just not the case. The real killer in that comparison is that people really don't want to live near a nuclear plant and in any case, regulation and such politics makes it hard or impossible to scale up nuclear power in that way.
And that's true even assuming instant capacity adaptation. It's just not efficient to keep nuclear power at a capacity lower than their peak capacity.