System that monitors the operation of a reactor and which, on sensing an abnormal condition, automatically initiates actions to prevent an unsafe or potentially unsafe condition. This use of the term protection refers to protection of the plant (protection (2)). The 'system' in this case encompasses all electrical and mechanical devices and circuitry, from sensors to actuation device input terminals. Safety Actuation System: The collection of equipment required to accomplish the necessary safety actions when initiated by the protection system. Safety Related Item: An item important to safety that is not part of a safety system. Safety Related System: A system important to safety that is not part of a safety system. A safety related instrumentation and control (I&C) system, for example, is an I&C system that is important to safety but which is not part of a safety system. Safety System: A system important to safety, provided to ensure the safe shutdown of the reactor or the residual heat removal from the core, or to limit the consequences of anticipated operational occurrences and design basis accidents. Safety systems consist of the protection system, the safety actuation systems and the safety system support features. Components of safety systems may be provided solely to perform safety functions or may perform safety functions in some plant operational states and non-safety functions in other operational states. Safety System Support Features: The collection of equipment that provides services such as cooling, lubrication and energy supply required by the protection system and the safety actuation systems. After a postulated initiating event, some required safety system support features may be initiated by the protection system and others may be initiated by the safety actuation systems they serve; other required safety system support features may not need to be initiated if they are in operation at the time of the postulated initiating event