I was trying to get into the biogas and nuclear reactor topic. When i noticed the fermenters needed heat and fluid reactors exchange heat, this came into my mind. It creates a whopping 6.5k EU/t (+-), while only using 2 quad uranium cells per cycle and 1 biochaff every 8 seconds(+-). The reactor design itself isn't mine, i got it from the reactor tutorial post. It provides heat for (almost) 14 fermenters, fueling around 280 fluid fireboxes, each producing 32 HU/t, converted to 24 EU/t.
The reactor itself would only yield 240 EU/t or around 1000 EU/t in Fluid Mode. When we consider that the reactor runs at efficiency 6, the total efficiency would be around 160 (minus whatever 1 biochaff every 8 seconds counts)
Please don't ask me about the building costs