> the biggest reason is nuclear simulations There is this mythical thing about the nuclear simulations. The national labs run the baddest supercomputers out th

> the biggest reason is nuclear simulations There is this mythical thing about the nuclear simulations. The national labs run the baddest supercomputers out there, and they are involved in the nuclear stockpile stewardship, so huge simulations must somehow be necessary. Either to maintain the nukes themselves, or at least to maintain them while respecting the comprehensive nuclear test ban treaty. Treaty that was signed but never ratified by the US, Russia or China, by the way. The reality is something like that. A fission bomb, when detonated, goes through about 50 or 60 generations of neutrons. Because of the exponential nature of the chain reaction, most of the energy comes from the last 10 or 20 generations. You can adjust the power of the implosion so that you trigger only 10 or 20 or 30 generations of neutrons. At some point you get enough heat from the reaction that the core melts; such a test is called "hydronuclear" and CIA has strong evidence that Russia performs hydronuclear tests. You can also adjust the implosion that you get a chain reaction that is subcritical (each new generation has fewer neutrons that the one before). All nuclear powers perform subcritical tests. The difference between subcritical and hydronuclear tests is only a theoretical one. There are no means to monitor a state for hydronuclear tests (other than human intelligence of course). China does not need supercomputers to maintain a cutting edge nuclear force. After all, the US and the USSR had such nuclear forces 50 years ago, when the entire computing power of the world was less than what my iPhone can provide to me right now.