nuclear plants can cut power as quickly as any other power plant, you are just controlling steam. divert the steam from the turbine and you aren't generating power anymore.
I agree with that, I have just seen on here before that people think you can't regulate the electrical output of a nuclear plant like with more traditional ones.
Halving the output essentially means doubling the price.
For Vogtle halving the expected capacity factor means the generated electricity now costs a completely stupid 40 cents per kWh or $400 per MWh.