You can sustain both Mk II reactions:
lithium-aluminium - clay dust. You can duplicate clay with TC.
beryllium-deuterium (I'm going with that recipe, almost ready to switch the reactor to Mk II) - deuterium is self-explanatory. Beryllium - enderman farm, and processing the pearls into molten beryllium. Isn't that hard, but you need a good mobfarm for that. I'll post screenshots when I'm done with Mk II.
I still haven't started on the thorium reactors though :/ Would the designs you and Dark posted way earlier still work well? Or is there some better design? How many reactors should I make? I have over 10k thorium.
Ah, nice. Good to know. And, yeah, I forgot about Beryllium from Ender Pearls. I have a great Ender Pearl farm already. I think I'll do the Berrlyium + Deuterium recipe. Seems slightly more "legit" for the fuels, assuming you can grok Ender Pearls...whatever those are in RL, heh.
Regarding the Lutetium, any design will work, but the ones that use more rods at a time will produce Lutetium faster, so go with the at least a 5x quad-core design. The key is automation. And, build several of those. It's taken me a couple of weeks with 4 Thorium reactors running pretty much 24/7 to make 400-ish Lutetium.
But, if you're at Mk II, you may have enough power to brute-force Replicate (UU-Matter) up enough Lutetium with a simpler setup than building an array of Thorium reactors with all their little components in the reactor itself.