You understand they have to take the plant offline to do major maintenance, even refuelling, right? In April, 75% of New England's nuclear power plants were offline, for instance, most unplanned.
When a single plant costs billions of dollars and becomes a significant or overwhelming contributor to an area's power mix, it can be a problem.
A typical nuclear plant isn't designed to be cycled regularly. What you are suggesting is that most nuclear plants are not generating power for more than 50% of the time.
A cursory search of capacity factors will show that this is the opposite of reality. A typical wind or solar installation on average, generates zero power for more than half the time.
Please be a bit serious about what you're saying, you don't have to actually turn of a plant when you need to refuel. If any kind of plant (including hydro) need to be completely turned off for maintenance its really because you had a major design flaw.
Here's a nuclear industry blog post explaining the practice: http://neinuclearnotes.blogspot.com/2012/05/what-happens-dur...
It's remarkable how much power these plants generate with a relatively small footprint.