I've been messing around for a couple of days on creative trying to get the smallest high-power bucket CASUC... and after like 5 reactors made, I finally got a good one which I believe is one of the smallest (if not the smallest) high-power bucket CASUCs.
It uses IC2, Redpower5, Nuclear Control (just to monitor the reactor) and Iron Chests (optional).
The chests act like "reservoirs", they can be anything (normal chest or any other material if using Iron Chests mod), although the bigger the better. Now you're probably asking why reservoirs? 1) They always have extra coolant if needed. 2) With them, the amount of buckets grabbed by the system is "automated", this means that if for some reason buckets are lost, it will grab just the necessary buckets without overflowing the system (if you put too many buckets it will get stuck). 3) Easy to see if there aren't enough buckets. 4) Easy to add/remove buckets. 5) Prevents heat spikes due to lack of buckets.
The cooling system has 4 deployers, 4 filters to retrieve buckets from the deployers and put in chests, 4 filters to grab them from chests and put into the reactor and 4 more filters to take the empty buckets out of it. So the buckets go deployer > reservoir > reactor > deployer. Also it doesn't use any EU to cool the reactor.
The reactor can complete a full cycle without even getting close to near-meltdown temperatures, outputting 1970EU/t.
If you're interested on a tutorial on how to build this just ask... I can make one.
PS: I'll make a control panel for it somewhen