Measures and method characteristics for early evaluation of safe operation in nuclear power plant control room systems

Safe operation is a central objective for high-risk industries such as nuclear power plants. Operation of the plant is managed from a central control room, which is a complex socio-technical system of physical and organisational structures such as operators, procedures, routines, and operator interfaces. When control room systems are built or modified it is of great importance that the new design supports safe operation, something that must be evaluated during the development process. Summative evaluations at the end of the development process are common in the nuclear power domain, whereas formative evaluations early in the process are not as customary. The purpose of this licentiate thesis was to identify demands on evaluation methods for them to be suitable for early assessment of the control room system’s ability to support safe operation. The research consisted of two parts: to explore evaluation measures relevant for nuclear power plant control room systems, and to identify requirements on evaluation methods for them to be useful in early stages of the development process. To explore the issue of evaluation measures two interview studies were performed with various professionals within the nuclear power domain. The purpose of the first study was to investigate aspects contributing to safe operation, while the second study sought to identify design trends in future control room systems and their potential usability problems. To complement these empirical studies, other researchers’ choices of measures for control room system evaluations were analysed. The results showed that a combination of measures from six categories is necessary to fully access the control room system: system performance, task performance, teamwork, use of resources, user experience, and identification of design discrepancies. In addition, the resilience engineering perspective should be considered in control room system evaluations in order to assess the ability to handle unanticipated events. Requirements on evaluation methods were investigated through analysis of characteristics of early product development phases. The result was that system representations in these phases are more conceptual, and that using these representations to perform tasks differs in some aspects from use of the final system. Empirical methods that directly study user interaction with the control room system are therefore less suitable for early evaluations. Analytical methods that study use indirectly are a better choice. An additional identified requirement is that if methods are to be utilised in industry, practitioners must find them useful in practice. To conclude, further work is needed to identify useful analytical evaluation methods that can assess measures from the six categories. Suitable methods for early assessment of the capacity for resilient behaviour is another topic that needs further exploration