It is rarely noted this downside of nuclear. Yes, they can produce electricity 24/7 at full power... until they don't. If there is a technical problem, they have to shut down. As you said, there are environmental conditions forcing them shut down. And if a nuclear power plant shuts down, typically a whole GW or more is dropped from the grid. France has recurrently shortages in electricity production, if too many nuclear power plants are off the grid. In the last winter, in Germany about 50% of the nuclear power plants were off grid for various reasons (mostly maintenance) too.