100% renewable isn’t enough right now. Batteries cost too much. 70% renewable and 30% nuke isn’t a bad mix though.
Batteries have been falling in price by 27%/year recently, and PV by nearly that much, so it's a bold position to assert this will suddenly stop.
Now, is it possible that a new type of battery will appear and take over the market by 2030? Yes. Will there be enough of them to compete with the stabilizing power of a nuclear power plant? Maybe. Will there be enough nuclear + storage so that the best use of that storage will be to shut down the nuclear plant? Absolutely not.
Basically, we need massive amounts of new electrical power (so we can transition transportation to electrical), and we need to shut down all fossil fuel power generation yesterday. Since we can't have enough storage yet for an exclusively green grid, nuclear shouldn't be competing with green energy in this discussion. Our choices are not "all green by 2030 VS green by 2030 + nuclear", they are "green + coal/gas by 2030 vs green + nuclear + less coal/gas". If we're instead talking about 2100, or 2200, then yeah, well probably be able to shut down nuclear as well.
The best use of a nuclear power plant is not to build it at all. Having not built it, the storage built instead at a tiny fraction of the cost will certainly be more than enough to replace it.
Building any nukes means, for each, building several times less new renewable generating capacity than could otherwise be.
(The "synthetic baseload" comparison is favorable to nuclear, as dealing with variable demand can only help renewables as it already requires storage, and that storage can serve double duty in the variable demand case. Similarly dispatchable demand and transmission between countries also only helps renewables.)
It's difficult to get nuclear to compete with wind+solar+batteries+hydrogen in the 2030 cost scenarios. Nuclear does least worse in places like Poland then.
There are many alternatives to batteries, for longer term storage. Tanked anhydrous liquified ammonia may be common, particularly for smaller and more isolated utility districts, in part because tankage can be topped up from imports if it runs low.
Underground or sea-floor compressed air are practical, as is buoyancy, in many places. Many more places can use pumped hydro than have an existing dam, or watershed; either up a hill or down to an underground cavity.
The method used will be whatever is cheapest in the place and time constructed. Cost for most methods is falling fast.
Building a nuke is by far the most expensive baseline alternative, provided it can even be approved and built on a useful schedule.
Nant de Drance has 900MW of storage, and took 14 years to build. Each of the last generation reactors in Hanul generate 950+MW of power, and took 5 years to build. The first newer generation reactor is 1340MW, and (assuming it keeps its schedule) has taken 10 years to build. They've done the first tests so they have some chance of connecting to the grid this year, but let's be pessimistic and say that it will take another 4 years - matching the construction time for Nant de Drance.
That's still ~50% more power, and it is actually generating it: for Nant de Drance to help, it also needs >900MW of actual renewable power generation plants to be built and operated.
There is little economy of scale, in pumped hydro. California stores a much larger amount of energy in numerous reservoirs all over the Sierra Nevada range.