![]() Otherwise this sphere will simply heat up and boil. ![]() Even in the extremely unrealistic scenario when nuclear fuel made of pure metallic weapons-grade uranium or plutonium (something that simply doesn't exist - see below) melts down and forms a perfect sphere of critical mass, it still needs one more condition to explode: for this mass to be squeezed into the critical radius, achieved in bombs only under tremendous pressure created by chemical explosives and in a very short (on the order of milliseconds) time window. A core for a nuclear weapon needs a near-spherical shape for any kind of runaway chain reaction, and depending on size and material may also need a neutron reflector. A nuclear reactor simply cannot cause a full-scale nuclear explosion: fuel assemblies are arranged into long, thin columns separated by cladding the large surface area causes a significant percentage of the available fission neutrons to dissipate into the moderator rather than causing further fission events, preventing a critical mass from forming. Similarly, fictional nuclear reactors will meltdown or go up in gigantic nuclear explosions at the slightest thing going wrong.This is why most of Japan's nuclear reactors shut down safely during the 2011 earthquake, as the failsafes for their SCRAM systems kicked in (or were activated from the control room) at the appropriate time. If the power to the safety systems is interrupted even for a moment, the mechanism stops resisting and the reactor shuts down. Usually, the SCRAM mechanism has to actively prevent the shutdown from happening - for instance, by constantly pushing against a spring, or holding up control rods with an electromagnet. What's more, even the failsafe have "dead-man" failsafes. A switch that usually exists in multiple redundant locations both near and far away from the reactor room, so that you can always reach at least one during an emergency. This is as opposed to real life, where it's typically an automatic safety feature which engages if the reactor shifts outside a certain set of safe operating parameters and where a manual reactor SCRAM is as simple as turning a switch. If a reactor does melt down or is going to melt down, the hero usually has to manually initiate a SCRAM, an emergency shutdown, sometimes going to elaborate lengths to set the SCRAM up or even having to manually insert the control rods into the reactor one at a time.It should be noted though, as the narrator repeatedly assures us, that these bombs do not actually contain radioactive material "so as not to waste this precious resource", defeating the point of the tests somewhat. In fact, here's a film produced by the US Air Force back in 1960 showing nuclear weapons being purposely dropped out of planes, set on fire, and otherwise subjected to movie-of-the-week hijinks to demonstrate that rough treatment of nuclear weapons does not result in said weapons detonating.Blunt force will not set off a nuclear weapon either, no matter how hard. In fact, partial detonation of the explosives will disable the nuclear weapon (but probably contaminate the area with radiation). High precision engineering is required to get everything to come together properly if things are off by even milliseconds, the yield will be dramatically reduced and it may fizzle entirely. The explosives are directed inward in order to generate the necessary chain reaction. note The standard setup for a nuclear bomb is a sphere of weapons grade fissile material surrounded by conventional explosives. Shooting, or even blowing up a real-life nuclear weapon with conventional explosives is likely to disable the warhead, not set it off. to achieve a full-scale explosion (mainly a sphere of conventional explosives being set off in unison around the nuclear mass, compressing it to supercriticality and initiating a nuclear reaction) while fictional nukes act like spheres filled with mega-nitroglycerin. In real life, a nuclear weapon requires precise conditions note The precise engineering of a nuclear weapon makes the best Swiss watch look like a flint knife in comparison.It doesn't matter if it's designed not to do that, it doesn't matter if it's not fissile enough to be used for an atomic bomb, it doesn't matter if it hasn't got enough material for critical mass, it's gonna blow. Related to Reliably Unreliable Guns and Stuff Blowing Up, if something is nuclear, and something, anything happens to it, it's Going Critical and gonna blow up like an atomic bomb.
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