Which is great when the sun's up and the weather is good. Similar deal for wind power, it's great when the conditions are good. We still haven't got very large scale storage where we need it to rely on renewables full time. Nuclear helps while we sort out storage but we need to be very, very careful about corruption - if corporations can screw over the public for money they've demonstrated that they will, and nuclear implementations cost a lot of money.
Nuclear power is not exclusively used for AI. Additionally, if they have their own power, then that frees up whatever energy they use for AI from other plants to be used for other purposes.