The other day I had finished my plutonium reactor to generate lots of lovely EU for my massfab. The layout of the reactor is shown here. I'm using a combination of golems and AE autocrafting to recharge the LZH condensators, which are fed by lapis bees. I even installed a nuclear control heat monitor to shut the reactor off if it got too hot (thought thats only an issue when the condensators are being replaced). Since the heat output of the plutonium cells is less than the reactor can produce before the heat monitor kicks in, there's no way it could explode. Guess what just happened?!? The entire thing is chunkloaded, and it managed a full cycle before without any problems. If anyone could answer the question in the title, please let me know. By the way, if you're wondering how I got that much plutonium, I re-enabled the 8 depleted cell recipe in the GregTech configs.