I am trying to understand the fixed cost of a nuclear power plant relative to variable cost. By fixed cost I mean "cost that does not vary with the amount of the power outputted over a given time period." By variable cost I mean "cost items that vary with the amount of the power outputted over a given time period." Does the whole plant have to be either on or off? Or can its output be scaled down pretty much on a continuum? Or perhaps on a discrete scale? In either case, what are the cost savings during scaled-down times, e. g. off-peak demand, relative to total cost of operating?