Scram

A scram or SCRAM is an emergency shutdown of a nuclear reactor effected by terminating the fission reaction. It is also the name that is given to the manually operated kill switch that initiates the shutdown. In commercial reactor operations, this type of shutdown is often referred to as a "scram" at boiling water reactors and a "reactor trip" at pressurized water reactors. In many cases, a scram... (Wikipedia)