The CICA concept for use in the MERMOS method redefined by a new organizational reliability model

MERMOS is the reference method used by Electricite de France (EDF) for Human Reliability Assesment (HRA), to assess the emergency operation of nuclear reactors during incidents and accidents for Probabilistic Safety Evaluations (PSA). This is a second-generation HRA method, designed based on EDF’s accumulated experience gained in observing simulated reactor behaviour and by analyzing publicized incidents, such as the accident at the nuclear power station at Three Mile Island in 1979. One of the first things to emerge from our work was that the concept of individual human error is insufficient by itself to explain why a team of operators fails to control a reactor during an accident. A second important conclusion relates to the concept of human failure, as applied to highly reliable technical systems requiring cooperative operation. Defining operational failure as a discrepancy from the successful operation (meaning that actual behaviour deviates from the expected behaviour, defined in terms of the type of task involved and organizational requirements) leads to deadlocks, because the instructions issued to operators often conflict. As an example, operators are both required to comply with their set procedures to the letter; and to act on their own initiative. To overcome these limitations, MERMOS sets human error in a collective context and explains it as the persistence of consistent behaviours that it describes using the concept of CICA (Key Configuration for Accident Management - Configuration Importante de la Conduite Accidentelle). We propose a new general organizational reliability model for a system such as a nuclear power station, aimed at clarifying the concept and at the same time, redefining human error as it applies in such a context.