To abort a nuclear reaction in an emergency. Originally, the fuel rods were held in place over a retardent material by ropes. In the event of an emergency, a guy with an axe stood at the ready to cut the ropes, dropping the fuel rods into the control material, thus halting the reaction. Acronym for Safety Cut-Rope Axe Man.
OMG d00d! t3h reactro is going to blwo up!!!!!1 SCRAM it!!!!!11~