There is a pretty good big reactor setup with minimal waste that requires 25 fuel rods 20 diamond blocks and 16 buckets of liquid ender. the entire structure is 7x7x7(inside is 5x5x5) just have the 5 rods in the center in an X shape with diamond blocks on the middle sides with ender flowing from the top. Makes about 11.5k rf/t with the least amount of waste per rf (i dont know the math for it)I made one with 15, Had to use diamond blocks tho since I'm out of Electrotine, still getting almost 8k rf/t so it solved the issue. ;-) (have the setup tied to a power monitor to turn on/off the recycler setup)
That allowed my iridium build to finish up over night, now at around 100 Iridium. ME storage here I come.