A grid running 70%+ renewables needs massive storage, transmission overbuild, and firm backup capacity costs that don't appear in solar/wind LCOE figures but are real and substantial. Nuclear provides firm, dispatchable, carbon-free baseload with a ~90%+ capacity factor. Solar capacity factors are 20-30%, wind 30-45%.
The OECD's 2020 Projected Costs study shows that at a 3% discount rate with a $30/ton carbon price, nuclear was the cheapest dispatchable option in most countries. Nuclear becomes comfortably cheaper than coal and gas under carbon pricing at low discount rates.
Not that nuclear power plants create weaponisable isotopes, they don't, but having a healthy functioning nuclear industry really helps.
The decision was made in response to Fukushima, 15 years ago. Generational trauma from Chernobyl probably played a role as well. How does this relate to nuclear weapons at all?
It's the only real deterrent against Russia. But nuclear power I'm not in favour of due to the long-term waste and potential safety impact.