Display MoreMOX fuel works exactly like ordinary uranium when in a fluid reactor except that if the reactor temperature is greater than 50%, the MOX fuel generates twice as much heat, and thus double the efficiency.
If you want to maintain a high reactor heat (in order to get that massive efficiency boost) that doesn't need to be manually generated again every time you start the reactor or replace the fuel, then you need to rely on inter-component heat conduction only. This puts a hard cap on reflectors to just 3 instead of 4 because you need one side available to conduct heat to components. However, it is not possible to remove all of this heat as fast as it is generated because it will be generating 672 heat per second. The fastest that heat can be drawn away from one component is 216 heat per second, which requires that the component be a component heat exchanger with three more component heat exchangers around it. With a duty cycle of 19 seconds off, 9 seconds on, the 672 heat per second generation will be reduced to 216 heat per second. The reactor design shown in your second image will work given this duty cycle, but it has more vents than needed. This reactor design has the exact amount of cooling required for the cycle of 19 off, 9 on:
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While this works, it is very close to melting as the component heat vent adjacent to the MOX fuel will reach 4,824 heat at the end of every 19 second on-cycle, and the component heat exchanger melts at 5,000. So, it doesn't exactly have a wide safety margin.
If you are alright with having to manually recharge the reactor heat every time the reactor starts up or is refueled, then you can have 4 reflectors around your MOX, but this requires a very precise balancing act and can extremely easily turn your reactor into a crater, even if the setup is perfect. Only do this if you either don't care about safety or absolutely require maximum efficiency. In order to make it stable while running, you must draw the exact amount of heat from the reactor that is being produced, and have a vent setup that can sustain being in a very hot reactor indefinitely (i.e. no under-cooled overclocked heat vents, because they will melt). Again, it will not be possible to cool all the heat produced, because it will be making a whopping 896 heat per second. This means we will again need a duty cycle. But unless you have a very short duty cycle, a simple cycle will not work because you only have 5,000 heat of spare room before your reactor explodes. Anyway, the best design that I'm aware of (the last design on the first post of this thread) cools 640 heat per second and requires a duty cycle of 5 seconds on and 2 seconds off. This means the reactor heat fluctuates by 1280 heat during operation. Given only 5,000 heat of operating room, this means you need to set the temperature within a range of only 3,730 heat to keep it simultaneously above 50% heat and below 100% heat at all times. Plus, every time you shut down the reactor for any reason, e.g. refueling, it will lose all its heat and require you to somehow restore its heat to somewhere in the 3,730 heat wide safe zone. This is made very difficult because as soon as the temperature rises above the magic 50% line, it will start generating 448 more heat than it was while it was below that temperature, and it only takes 11 or 12 seconds to explode at a heat gain rate of 448 heat per second. As such, this is an exceptionally dangerous design. I do not recommend using it unless you have a mod like nuclear control which can give a redstone signal when the temperature is above some threshold. If you do have such a mod, then it will be much safer when running, but when you start it up you'll still have that 10 second time limit to restore all cooling because you'll have to remove at least half of the cooling to get it to rise above 50% heat.
OK. I have built 81 mox reactors. Each gives out 500 EU/tick, for a total of 40.5 kEU/tick. Good energy.