Originally an acronym for Safety Control Rod Axe Man, a term used to refer to the person assigned to the duty of dropping the boron control rods into the "pile" at the University of Chicago in case of emergency. This task was accomplished by cutting the supporting ropes with an axe and allowing the rods to drop into the core by natural gravitational forces.
Unclear, conflicting sources are probably backronyms.
- The emergency shutdown of a nuclear reactor, originally specifically by insertion of one or more safety control rods.
- In a more general sense, an emergency shutdown.