I have no idea about nuclear & reactor physics. please feel free to post any and all ideas you might want to see in GTC here

add fuels made in Actinide series
like a nuclearcraft , better than nuclearcraft

RTG stuff

A Pebble bed reactor is supposed to be one of the safest ones to run.

more enriched fuel rods

enriched thorium fuel rods

centrifuging depleted enriched fuels receives for example : plutonium infused ender pearl, plutonium infused redstone, plutonium infused charcoal, plutonium infused blaze rod, plutonium infused nether star

Fission fuel processing chains that would make items used in fusion reactions

add tier 2 steam or normal nuclear reactor , add nuclear chamber extension
add 2d texture to fuel rods
placeable uranium rods and enriched versions

A reactor steam pipe. A pseudo-fluid pipe that can just pump steam, but unlimited amounts. Only accepts input directly from reactors (and maybe Railcraft boilers if going the compat route) and outputs into any other connections (that are not reactors). Would make IC2C steam reactors actually usable.