Developed as a remedy-oriented system for systematically analyzing and evaluating human-related incidents occurring in nuclear power plants, the present system aims particularly at identifying causal factors and at deriving proposals for specific hierarchical countermeasures. Unlike conventional methods, which are based on checksheet format, and are thus devoid of logical methodology for conducting the analysis, and which thus lack the means of searching for underlying causal factors, and which do not record factual information on the sequence of events, our system incorporates innovative techniques such as; (a) a modified fault tree method for searching the underlying causal factors, (b) compilation of related events into sequential charts, (c) technique for devising proposed hierarchical redundant countermeasures, and (d) implementation procedures set out in practical manual form for easy familiarization and application. Through several trial applications, our method has proved to permit identifying underlying causal factors even down to those associated with the software aspects of human action and state of mind, and with the mode of management, organization, operating rules and document forms, all of which are liable to be overlooked. The results of analysis are stored in database to permit subsequent searching to serve as useful material for activities aimed at promoting plant operation safety.
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