Actually coal and nuclear can only do base load: thermal power plants need hours to shutdown or to ramp up. That's why hydroelectric or gas peakers are needed for daily variations (peak hours).
So 100% nuclear is not doable.
Renewables plus batteries have no such issues. Imagine you want to equip your house: batteries for 24h and enough PV to handle the worst day of the year (a cloudy winter day). Done, you have 100% renewable 24/7. Super reliable. Want more reliability? Add more PV, more batteries.
Since nuclear had lost the battle of the costs, they invent nonsense rationale to try to save their industry.