Green Energy

Why would an all nuclear grid need more than a day of storage?

Technically they need 200,000 years worth of storage. Although in that case it's more archival.

And you can't just balance load with nuclear reactors, they take forever (as in days to weeks) to spool up, you can't just switch them on. So you're still going to need some storage capacity and if you're going to have storage anyway you might as well have a simpler energy generation system to boot without all of the big complicated nuclear reactor equipment.

Plus of course the fact that you can stand up solar panels and wind turbines almost anywhere in 6 months, but you'll be wrangling for 30 years to build a new nuclear reactor.