This paper researched the safety functional requirements analysis and the allocation of functions between man and machine for the nuclear power plant. The safety functional requirements are identified from accident handling needs and refined from system configuration consideration. Through the analysis of design conditions, some safety features were extracted to mitigate accidents. Then, components (e.g. pumps, valves, tanks) were determined to implement each of the safety features at the system design stage. At this stage, some implicit safety features, which could not be obtained directly from the accident analysis, were added, according to the specific conditions of system configuration and operation. Finally, after further judgement on possible inconsistency, a complete list of safety functions for the nuclear power plant was formed. As an illustration, this paper provided a list of safety functions related to the safety injection function, and a list of equipment for the safety injection system. Furthermore, these identified safety functions, were appropriately allocated between man and machine, to be performed either by system components automatically, or by operators locally or remotely from the control room, or under the cooperation of operators and system components. Seven factors were considered in the allocation: a) performance requirements; b) the capability or limits of man and machine; c) existing practices; d) operating experience; e) management requirement; f) technical feasibility; g) cost. The allocation of functions for the safety injection system was validated using a simulator.

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