Actually, nuclear is not generally regarded as renewable energy by definition [0].
I can somewhat see the reason (of course, it's arguable) in the fact that there is some identification of renewable sources of energy with their "cleanness".
But how can you call solar power 'renewable'? It's powered by fusion reactions in the sun, which are finite; it's going to run out.
Only partly tongue-in-cheek. Fission power will also last hundreds of millions of years, so although it is "non-renewable", it shouldn't carry the same connotations of "will therefore run out".
I can somewhat see the reason (of course, it's arguable) in the fact that there is some identification of renewable sources of energy with their "cleanness".
[0] Quick google search! And wikipedia page: https://en.wikipedia.org/wiki/Nuclear_power_proposed_as_rene...