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| - What any device called a reactor does. May be called "a meltdown", "destabilizing", "going critical", or something more fanciful. The failure of an actual nuclear reactor will often be described with the actual term "meltdown", but it will not resemble any meltdown known to science. The resulting explosion will be suspiciously similar to that of an atom bomb, or at least large enough to blow the vehicle/facility in question to pieces. Alternately, if the main result is a release of radiation, it will be described by a huge red circle on a map. The size and danger level of the circle may suggest even more death than an atom bomb would cause.
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| abstract
| - What any device called a reactor does. May be called "a meltdown", "destabilizing", "going critical", or something more fanciful. The failure of an actual nuclear reactor will often be described with the actual term "meltdown", but it will not resemble any meltdown known to science. The resulting explosion will be suspiciously similar to that of an atom bomb, or at least large enough to blow the vehicle/facility in question to pieces. Alternately, if the main result is a release of radiation, it will be described by a huge red circle on a map. The size and danger level of the circle may suggest even more death than an atom bomb would cause. Sci-fi reactors are usually based on the idea that a nuclear reactor is a continuous nuclear explosion in a really strong box. By extension, reactors in the future are a different Sealed Evil in a Can, just waiting to blow the hell out of everything once the shielding is cracked. These reactors are almost a Chekhov's Gun situation. Calling any device a "reactor" is your cue to expect a spectacular explosion. A drive strands a ship in deep space, a generator subjects characters to an environmental hazard, a reactor removes something from the plot forever. In real nuclear physics, "critical" means the reaction sustains itself. A reactor is critical if it's on. Relatedly, "supercritical" simply means the reaction is increasing in power. An explosive surge of power requires the reactor to go prompt critical, something that may have happened only once by accident (in the SL-1 reactor accident and maybe at Chernobyl, but the consensus is that it was more likely to have been a steam-explosion like an overloaded household water-heater but moreso). Even in that case, the reactor will explode well before the power output reaches atom bomb levels. (Designed bombs, on the other hand, go prompt supercritical.) To be specific, making a nuclear explosion not only requires compressing a mass of fissile material - something that emphatically does not happen in a nuclear reactor - but keeping it compressed for a long enough time, giving the runaway "prompt critical" reaction the time it needs to build up a bang. This is a very exact science: explosive lenses, drivers, and the fissile core have to be fitted perfectly, using machines so precise that they are overkill for polishing glass lenses. If anything is off by the slightest bit, you wind up squirting fissile material out of the spots of weak pressure in the detonation shockwave, which makes a radioactive mess but doesn't make a bang. Meltdowns are just that - the fissile core melts into slag, hot enough to flash coolant into steam (wherein you get the associated bang) and possibly melt through the reactor vessel. Since reactors currently in use are designed with safe failure modes in mind (including the famous manually triggered SCRAM) the worst you really get from a on a land-based reactor meltdown is that the reactor pile becomes a pile of reactor. It makes a very expensive mess, but isn't going to destroy much of anything outside the reactor containment facility itself, much less wipe a city off the map like nuclear bombs are capable of doing. On a sea vessel, however, the contamination would be catastrophic: the reactor mass would come into direct contact with the seawater, and shatter or even be entirely vaporized to small particles (fallout) in the massive subsequent vapour flash explosion. Radiation will be an issue inside the facility, but widespread fallout of the kind associated with nuclear war won't be a problem unless the containment systems have been ruptured... which, give that there was probably a steam explosion during the meltdown, they very well could have been — and, indeed, in both catastrophic meltdowns that happened in reality the containment was breached, resulting in massive contamination. Long story short, a meltdown is extremely bad news, but orders of magnitude less bad than even small (ie tactical) nuclear weapons. And in case you wondered, a "reactor" is something where a reaction happens. By no means it has to be a nuclear reaction, and chemists sometimes use this word as well. But in fiction it's always nuclear. Needless to say, this trope can be considerably more Justified Trope if you've set your work in a world where the laws of physics are expressly different from those in reality. After all, if the Incredible Hulk can survive a gamma bomb explosion at point blank range without being incinerated and instead be turned into a super-powered behemoth, then the laws of nuclear physics are obviously at least somewhat different than they are in Real Life. A case of Did Not Do the Research. See also Containment Field. When a reactor "goes critical" but is then turned off with no consequences, it's Instant Cooldown. Examples of Going Critical include:
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