If you've already provisioned enough nuclear plants to meet peak energy demand, producing less energy has no marginal cost. Alternatively, you can just keep operating at full capacity, and give energy away for free and use it for energy-intensive tasks like desalination or arc furnaces. The idea that we'd build nuclear plants that only operate a few weeks per year is a strawman of your own construction.
You're right that nuclear is more expensive than continuing to burn fossil fuels. And the reality is nobody has a plan to build fossil fuel free grid based on wind and solar. Absent a miraculous breakthrough in energy storage, solar and wind will always have to be deployed in tandem with fossil fuels. If we're looking at actually eliminating carbon emissions, nuclear is the only viable option besides geographically limited sources like hydropower.
You're right that nuclear is more expensive than continuing to burn fossil fuels. And the reality is nobody has a plan to build fossil fuel free grid based on wind and solar. Absent a miraculous breakthrough in energy storage, solar and wind will always have to be deployed in tandem with fossil fuels. If we're looking at actually eliminating carbon emissions, nuclear is the only viable option besides geographically limited sources like hydropower.