Your fuel cells are stupidly energy dense, which makes belt buffering a bit inconvenient. Consider a mod setting that allows reducing the power density of individual fuel cells, while maintaining the same overall power per craft by playing with ingredient/result counts for the recipes?

I'm not sure what you mean by belt buffering. The density was chosen for physical consistency -- the production is more expensive to match the energy density and both are normalized against a ton of other things in this and the chemical mod -- but this mod is going to need a complete rethink if I even decide to continue it for version 2.0 -- considering that in-game nuclear is no longer the end-game energy anyway.

I typically put my fuel cells on the inside of a belt that runs around the reactor block, and output used cells to the outside.
It would take ages to buffer it up to a satisfactory level, so I modded my personal copy of your mod. I reduced the energy of each cell by a factor of X, and increased their Presence in recipes by the same factor. The overall energy per rock is unchanged.