26 lines
3.7 KiB
HTML
26 lines
3.7 KiB
HTML
<?xml version="1.0" encoding="ISO-8859-1" standalone="no"?>
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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>scram switch</title><link rel="stylesheet" href="../../jargon.css" type="text/css"/><meta name="generator" content="DocBook XSL Stylesheets V1.61.0"/><link rel="home" href="../index.html" title="The Jargon File"/><link rel="up" href="../S.html" title="S"/><link rel="previous" href="SCNR.html" title="SCNR"/><link rel="next" href="scratch.html" title="scratch"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">scram switch</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="SCNR.html">Prev</a> </td><th width="60%" align="center">S</th><td width="20%" align="right"> <a accesskey="n" href="scratch.html">Next</a></td></tr></table><hr/></div><dt><a id="scram-switch"/><dt xmlns="" id="scram-switch"><b>scram switch</b>: <span xmlns="http://www.w3.org/1999/xhtml" class="grammar">n.</span></dt></dt><dd><p> [from the nuclear power industry] An emergency-power-off switch (see
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<a href="../B/Big-Red-Switch.html"><i class="glossterm">Big Red Switch</i></a>), esp. one positioned to be easily
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hit by evacuating personnel. In general, this is <span class="emphasis"><em>not</em></span>
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something you <a href="../F/frob.html"><i class="glossterm">frob</i></a> lightly; these often initiate
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expensive events (such as Halon dumps) and are installed in a
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<a href="../D/dinosaur-pen.html"><i class="glossterm">dinosaur pen</i></a> for use in case of electrical fire or
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in case some luckless <a href="../F/field-servoid.html"><i class="glossterm">field servoid</i></a> should put 120
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volts across himself while <a href="../E/Easter-egging.html"><i class="glossterm">Easter egging</i></a>. (See also
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<a href="../M/molly-guard.html"><i class="glossterm">molly-guard</i></a>, <a href="../T/TMRC.html"><i class="glossterm">TMRC</i></a>.)</p><p>“<span class="quote">Scram</span>” was in origin a backronym for “<span class="quote">Safety Cut
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Rope Axe Man</span>” coined by Enrico Fermi himself. The story goes that
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in the earliest nuclear power experiments the engineers recognized the
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possibility that the reactor wouldn't behave exactly as predicted by their
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mathematical models. Accordingly, they made sure that they had mechanisms
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in place that would rapidly drop the control rods back into the reactor.
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One mechanism took the form of ‘scram technicians’. These
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individuals stood next to the ropes or cables that raised and lowered the
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control rods. Equipped with axes or cable-cutters, these technicians stood
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ready for the (literal) ‘scram’ command. If necessary, they
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would cut the cables, and gravity would expeditiously return the control
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rods to the reactor, thereby averting yet another kind of <a href="../C/core-dump.html"><i class="glossterm">core
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dump</i></a>.</p><p>Modern reactor control rods are held in place with claw-like devices,
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held closed by current. SCRAM switches are circuit breakers that
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immediately open the circuit to the rod arms, resulting in the rapid
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insertion and subsequent bottoming of the control rods.</p></dd><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="SCNR.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="../S.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="scratch.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">SCNR </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> scratch</td></tr></table></div></body></html>
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