The CESA method and its application in a plant-specific pilot study on errors of commission

A pilot study on errors of commission (EOCs) was performed for a Swiss nuclear power plant, with the goals of (a) evaluating PSIʹs Commission Errors Search and Assessment (CESA) method for identifying potential EOC situations, and (b) obtaining an estimate of the potential risk significance of the analyzed EOCs. The EOC search and screening process of the method proceeds from a given action to scenarios in which the action is inappropriate. A catalog of key actions required in the responses to the plant events is first compiled. This catalog is then used in a systematic search of context-action combinations, to obtain a set of situations with EOC opportunities to be examined in detail. The results show that the CESA identification process is feasible and effective: it is able to identify plausible situations in which EOCs may occur. A preliminary quantification of four of these has been performed; the analyses so far show that the situations identified in the pilot study deserve careful consideration. Although the identification approach in CESA covers a subset of EOC types, the demonstration of the CESA method in the pilot study and the resulting identification of EOC cases is encouraging in terms of progress on the issue of EOCs.