I recommend looking into base vs peak loading for the energy grid. Nuclear is good as base load power, batteries are good for peak loading and renewables are good for charging batteries.
It's fairly easy to mix nuclear and renewables technically, it just doesn't make much financial sense in most places, particularly if you have to build new nuclear or if you're not too near the poles.
you can't regulate the output from nuclear reactors fast enough
From the article:
"The company touts the microreactor’s solid core and advanced heat pipes, which enable passive cooling and also allow for autonomous operation and load following."
Load following to change your thermal output over minutes or hours isn't frequency correcting which isn't grid stability. Steam turbines can't change speed quickly. Some exotic closed CO2 turbine might.
But what you can't do is mix them, as you can't regulate the output from nuclear reactors fast enough to work together with renewable energy plants.