For those people trying to make a mox reactor mark 2-5 i made a very nice reactor design to work with. Im currently making some tests on it in creative. Il'e probably post some more about it once iv'e got my control system up and running.
If you want a more easily controlled reactor you can easily switch out 1 or 2 of the quad cores for dual cores and it will still work just as well. It will be less fuel efficient but the cycle time will increase a lot.
Ive tested it in creative and it works out really well if you have a control system that makes sure that the temperature does not reach to high temperature. I made it so it pulls an even 1000 Hu from the reactor core which makes it possible to produce either 500 mb of superheated steam for 750 eu/tick or 500 with stirling.
The efficiency of the design is extrordinary. even at 0 reactor heat it produces 960*2 heating units which amounts to 960 eu/tick of fuel with stirling or 1440 eu/tick of fuel with superheated steam. The heat produced also increases by A LOT as the hull temperature increases. I'm not 100% sure but i think the increase in HU is linear with the reactor hull temperature (0% is default and 100% is times 5). If the heat increases linearly it would mean it would produce 0,55*960*2=4800 Hu at 50% hull temperature. with superheated steam that is an efficiency of 4800*0,75/8/5= 90!
Also unlike regular cycled reactors this one produces power at a stable rate as it is always pulling heat from the reactor even when it is turned off. The only downside is that it produces "only" 500-750 eu/tick. However the mox fuel rods would last for a very very long time before they are consumed. if average is 50% heat it would be 4800Hu/1000 or 4,8 times it's regular lifetime.
Overall i think this shows some great potential for mox in the 5x5
Edit: for a stirling setup i would probably use something like this
Update: Ive tested the first reactor now and it works very well with some easy automisation from nuclear control.
I'm using a not gate and a nor gate, with a remote thermometer and a lever. The reactor shuts of both if the lever is deactivated and if the temperature goes over 21000 (65%) the temperature varies between 64% and 78%. It is producing a constant 1000 Hu/s and has been working stable for some time now.
60 seconds of fuel tics took a whole 5 minute and 28 seconds. which amounts to about 5,5 times more than its normal duration or 5500 Hu per fuel tick. This reactor has an efficiency of about 103,125 and would produce 825 million eu per cycle