Studies of safety and critical work situations in nuclear power plants : a human factors perspective

Sammanfattning: The purpose of this thesis was to develop and apply different approaches for analyzing safety in critical work situations in real work settings in nuclear power plants, and also to identify safety enhancing measures by using the framework of interaction between human, organizational and technical subsystems (MTO, man-technology-organization). A Cognitive Psychology as well as a Stress Psychology framework was used. All studies were related to the annual outage operational state where the need for coping with many infrequent tasks, often carried out under high time pressure, puts great strain on the staff and organization of the plant. Furthermore, all studies used self-report measures.In three studies the natural variations in the plant state, normal operation and annual outage operation, were used to explore human performance, work-related factors as well as coping and the operators' own resources and the relationship between them. In the annual outage condition high work demands, decreased sleepiness at night shift, more errors and less satisfaction with work performance quality was reported by maintenance as well as by control room operators. A relationship between high work demands and more organizational problems and reports of more frequent human errors and lower satisfactions with work performance quality was also identified in the annual outage condition. Moreover, a relationship between increased sleepiness during night shift, more frequent use of coping strategies and a higher frequency of human errors was reported.In two studies the Event and Barrier Function Model was applied to analyze the safety of barrier function systems inserted into work process sequences to protect the systems from the negative consequences of failures and errors. The model was also used to assess safety in relation to a technical and organizational change.The last study addressed changes in work performance and work-related factors in relation to a technical and organizational change of a safety significant work process involving increased automation and new staff. Only minor changes in work-related factors and work demands were observed, but after the change satisfaction with work performance decreased and the use of coping strategies increased.The results from the studies in this thesis suggest areas for improvement of the safety in nuclear power plant work situations concerning both work-related factors, barrier functions and the interaction between human, organizational and technical subsystems. The identification of work-related factors associated with human error and degraded work performance may also have implications for safety in other systems with high safety demands such as other process industries, transportation and health care.