When is it offline? A few days (or weeks) every 12-24 months?

I don't think it's a major problem with a network of nuclear plants, you can plan the fuel replacement and have a steady power supply (nationwide). You can control when the downtime happens, unlike in other power sources.

Obviously the grid needs to have a fleet of base load plants large enough that some can be periodically taken offline for maintenance. This is understood by everyone familiar with the issue and we shouldn't have to keep repeating it. Maintenance schedules also apply to every other type of power plant capable of handling base load.

Can't a nuclear energy plant run continuously? (Genuinely asking.)