MMOSA – A new approach of the human and organizational factor analysis in PSA

The results of many Probabilistic Safety Assessment (PSA) studies show a very significant contribution of human errors to nuclear installations failure. This paper is intended to analyze both the human performance importance in PSA studies and the elements that influence it. Starting from Man–Machine–Organization System (MMOS) concept a new approach (MMOSA) was developed to allow an explicit incorporation of the human and organizational factor in PSA studies. This method uses old techniques from Human Reliability Analysis (HRA) methods (THERP, SPAR-H) and new techniques to analyze human performance. The main novelty included in MMOSA is the identification of the machine–organization interfaces (maintenance, modification and aging management plan and state of man–machine interface) and the human performance evaluation based on them. A detailed result of the Human Performance Analysis (HPA) using the MMOSA methodology can identify any serious deficiencies of human performance which can usually be corrected through the improvement of the related MMOS interfaces.