Something I hadn't known till yesterday was that the chernobl nuclear reactor meltdown thingy was caused by the people running the reactor doing some dodgy 'tests' that hadn't been thought through properly I guess. but also because there were 3 +ve feedback mechanisms that mean control of output is not linear.. (Xenon in the fuel rods, steam doesn't dampen the reaction like water does and the control rods displace water but are not homogeneous in their behavior) I like the way alot of stories say it was down to 'violating safety mechanisms' and 'flawed reactor design' when mostly it was a planned intentional violation of safety mechanisms, with a poor planning / understanding of the reactor design. Although I guess its easy to say that in hindsight. link 1 link 2