2014-04-26 10:52:28 -04:00
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scram switch
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2014-04-26 11:54:15 -04:00
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n. [from the nuclear power industry] An emergency-power-off switch (see Big
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Red Switch ), esp. one positioned to be easily hit by evacuating personnel.
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In general, this is not something you frob lightly; these often initiate
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expensive events (such as Halon dumps) and are installed in a dinosaur pen
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for use in case of electrical fire or in case some luckless field servoid
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should put 120 volts across himself while Easter egging. (See also
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molly-guard , TMRC. ) Scram was in origin a backronym for Safety Cut Rope
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Axe Man coined by Enrico Fermi himself. The story goes that in the earliest
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nuclear power experiments the engineers recognized the possibility that the
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reactor wouldn't behave exactly as predicted by their mathematical models.
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Accordingly, they made sure that they had mechanisms in place that would
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rapidly drop the control rods back into the reactor. One mechanism took the
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form of scram technicians. These individuals stood next to the ropes or
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cables that raised and lowered the control rods. Equipped with axes or
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cable-cutters, these technicians stood ready for the (literal) scram
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command. If necessary, they would cut the cables, and gravity would
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expeditiously return the control rods to the reactor, thereby averting yet
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another kind of core dump. Modern reactor control rods are held in place
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with claw-like devices, held closed by current. SCRAM switches are circuit
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breakers that immediately open the circuit to the rod arms, resulting in the
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rapid insertion and subsequent bottoming of the control rods.
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