https://mods.factorio.com/mod/Nuclear%20Fuel
Make breeder fuel cells be used in the plutonium RITEG OR make normal RITEG use uranium (not uranium cells) and plutonium RITEG use plutonium (not breeder cells)

I'm not sure that RITEG on breeder reactor is possible. Why you don't like energy cells?

Just because in his mod there are no MOX or Plutonium fuel cells, so I think it would be better if it used plutonium instead of the breeder cells

But in https://mods.factorio.com/mod/PlutoniumEnergy MOX is already presented and has much higher energy.
One item with 4 GJ energy is not enough for second tier. Nuclear fuel cell has 8 GJ!

Yeah, that makes sense. Also I didn't know about that mod, seems nice!