A brief review of the history of alternate shutdown systems for LMFBR's is presented together with a discussion of the rationale used in developing six proposed general design criteria for such systems. A reactor shutdown system developed at Combustion Engineering, Inc. is described which uses a modified EBR-II type control rod system with a redundant second system similar to FERMI safety rods except that the scram mechanism is pneumatically actuated. Test results of a model of the pneumatic scram release mechanism operated in sodium at 1100 F are given.