Nuclear reactors must be periodically shut down for days to months at a time for maintenance. That fact often fails to be mentioned when the 'constant reliable' claim is raised. The Sun, on the other hand, rises each day.

Renewables 'on a large scale' become less reliant on storage. Their 'viability' depends on the grid connecting them. On a continent-sized grid the wind is very likely to be blowing. Coupled with full-scale decentralized storage, the viability question blows away.