I went from charcoal, to steam boilers, magma crucible lava, to thermal gens, methane, nuclear, and finally solar a few days ago. Nuclear reactors are just too underpowered. Of all the systems I've built, the investment/reward is way too low on the nuclear side. Every other system produced far more for the investment in space/time/resources. Keep in mind I also didnt even turn the thing on until I had completely surrounded the thing in tungstensteel blocks and automated it with routers and filters. When it started running I thought to myself "oh is this all?".
Not hard to see why solars look OP in comparison. Nuclear needs a huge boost. It ought to sit between fusion and solar. Best way in my opinion is to reduce solars by a factor of 2, then boost nuclear by a factor of 4 at least.
512 solar vs my one quad uranium reactor at 140. With my recommendation it would become 256 solar and 560 nuclear.