For reactor designs, you can look on the IC2 forums. Specifically,
this thread. It contains many of the best internal cooling setups currently known to the community - those that manage the best combinations of output, efficiency and building/running cost. You will only find "safe and sensible" design there though. For example, you will not find microcycle (unsafe) or condensator (super expensive) reactors.
The designs posted there, and the online reactor designer application used to make and display them, continue to remain valid for all versions of IC2 running on Minecraft 1.4.x, 1.5.x or 1.6.x. This also includes the new experimental builds for 1.6.x, although MOX fuel rods are missing. The reason is, the maker of the reactor planner has disappeared and the applet is no longer being updated.
As a result, you can make GregTech reactors with the online planner for GregTech 2.8x or earlier only. Newer GregTech versions (i.e. Ultimate pack and newer) are not supported. You will have to use the ingame reactor designer in the GregTech computercube for that.
But yeah, any design using pure uranium in the thread I linked will work perfectly fine with any version of IC2 you can get via the FTB launcher. All of them are Mk.I reactors, meaning they run forever without heat buildup.
For microcycle reactors (which is what you call those that you only turn on for short periods of time), you can try and read the discussions about DDoS / CRCS reactors. It's basically the evolution of microcycle reactors, where you build reactors too hot for self-cooling, but instead of turning them off, you hot-swap cooling cells and use external cooling towers to cool them back down.