Its not a matter of if the nuclear reactor can increase or decrease its output, its the economics of building a very expensive machine that you then only use so

Its not a matter of if the nuclear reactor can increase or decrease its output, its the economics of building a very expensive machine that you then only use some of the time. A massive chunk of the cost of the nuclear plant is actually having the plant and the people working on it, if you spent all that money and paid all these people to work there but only using half its actual capacity you've practically doubled the cost. To my understanding the per-kWh cost of the fuel for nuclear isn't the real expense, but smarter minds in the subject please feel free to correct me.