And if you have renewable sources that are much cheaper per kWh of output than nuclear, why charge those batteries with nuclear?
The first is that it gets you out of needing ordinary batteries, because instead of converting heat to electricity to batteries and back, you can take the heat generated by the reactor during the day, store it in an insulated vat of molten salt and then use that to drive turbines at night. This should be much cheaper than ordinary batteries because expanding storage capacity only requires having more salt in more vats, and salt is much less expensive than lithium batteries.
The second is that if you have a nuclear reactor for generating at night when solar doesn't, the incremental cost of also operating it during the day is lower than the solar generating cost. It can't recover its full fixed costs at the price of daytime solar, but as long as it can recover its incremental cost you still operate the reactor 24/7.
Moltex claims that interposing a salt store would allow these components to be made to non-nuclear standards, but as far as I know no regulator has agreed with that.
"Unproven" is a synonym for we haven't done it yet, so the only way to prove it is to build them, so building them is the solution to that rather than a problem that should prevent building them.
And if the only problem is regulatory but there isn't actually any reason not to allow it, this too has an obvious solution.
The justification for treating the cooling system as part of the reactor presumably comes from older designs where the active cooling is necessary for safe operation. For newer passively-safe designs, what happens to the heat once it's removed from the reactor wouldn't matter any more than what happens to the electricity once it's removed from the reactor.
And all that means that new reactor technologies are not going to be really available for decades, and will be competing not with renewables and storage now, but the renewables and storage that will be available for purchase decades hence.
Most high fuel efficiency designs are fast reactors, or they employ extra radiation source to "burn down" the fissile material.
Tax subsidies for renewables, at least in the US, are small compared to the levelized cost difference with nuclear.
If you look at Lazard's levelized cost of energy report, where wind is far cheaper than nuclear, they assume a 20 year lifespan for wind turbines. This is not unreasonable.