Nuclear fission is actually by definition the least renewable energy source
But if you go according the strict physical principle every energy source is non-renewable
The sun fuses a finire amount of hydrogen, earth has a finire amount of latent heat, the moon a finire amount of gravitational inertia etc.
And there's a little paradox if you think about it, how can fusion be non-renewable but solar, that use radiation from the sun fusion, be renewable?
But that's exactly the "problem", there's enough fertile material for potential millions of years of consumption, and that's for fission alone.
I think the debacle is more because the definition of "renewable" is a little arbitrary than the dilemma if nuclear is renewable or not