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