Scram vs. Amscray

Scram

A scram or SCRAM is an emergency shutdown of a nuclear reactor. It is a type of kill switch. In commercial reactor operations, this type of shutdown is often referred to as a “SCRAM” at boiling water reactors (BWR), a “reactor trip” at pressurized water reactors (PWR) and EPIS at a CANDU (CANDU). In many cases, a SCRAM is part of the routine shutdown procedure as well.

The etymology of the term is a matter of debate. United States Nuclear Regulatory Commission historian Tom Wellock notes that scram is English language slang for leaving quickly and urgently, and cites this as the original and mostly likely accurate basis for the use of scram in the technical context. A persistent alternative explanation posits that scram is an acronym for ‘safety control rod axe man’, which was supposedly coined by Enrico Fermi when the world’s first nuclear reactor was built under the spectator seating at the University of Chicago’s Stagg Field. It could also stand for “Safety Control Rods Activation Mechanism” or “Control Rods Actuator Mechanism”. Both of these are probably backronyms from the original, non-technical usage.