You're not getting it. You keep the plant on all the time. When you need to reduce power you insert the control rods. You lose some efficiency, but you do burn

You're not getting it. You keep the plant on all the time. When you need to reduce power you insert the control rods. You lose some efficiency, but you do burn the fuel less fast as well; you're getting so much energy out of the nuclear fuel it's irrelevant. This is established science and reactor design, it's not new. What I learned from a friend who works in power is there's red tape constrains on doing power variation which is why they don't do it.