This standard establishes functional and design criteria for nuclear power generating station "safety systems," that is, that collection of systems required to minimize the probability and magnitude of release of radioactive material to the environment by maintaining plant conditions within the allowable limits established for each design basis event. These criteria are established to provide a means of promoting safe practices for design and evaluation of safety system performance and reliability. The criteria herein represent an acceptable basis for ascertaining the adequacy of safety system performance and reliability. Adherence to these criteria does not necessarily fully establish the adequacy of safety system functional performance and reliability. However, omission of any of these criteria will, in most instances, be an indication of safety system inadequacy.