I have made an efficient reactor plan as it can go up to an efficiency of 6.46 with quad-uranium cells with iridium reflectors. Thick reflectors are actually less efficient in this plan.
Efficient Reactor Plan:
http://www.talonfiremage.pwp.blueyonder.co.uk/v3/reactorplan…w50g9g8jlnc6rcw
However it can be a bit expensive (with iridium reflectors).
Copper ingots: 1951
Tin ingots: 581
Gold ingots: 80
Rubber: 61
Coal:512
Feel free to modify the reflectors and cells, it can handle up to double-plutonium cells.