MERMOS : An extended second generation HRA method

MERMOS is the reference method used by Electricite de France (EDF) for Human Reliability Assessment (HRA), to assess the emergency operation of nuclear reactors during incidents and accidents for Probabilistic Safety Assessments (PSA). When type N4 reactors were designed, the previous method used for Human Reliability Evaluation (based on the THERP methodology and on data-gathering using a simulator, known as FH6) required development, as it proved largely unworkable for managing incidents and accidents using computerized procedures. Designing MERMOS has been an opportunity to redefine the concepts used in assessing human reliability. EDF is currently extending MERMOS to use for assessing behaviour before an accident and during a fire, as well as for the assesment of Human Factors missions planned as part of the Level 2 Probabilistic Safety Evaluations (that take into account the release of effluent once the core begins to melt down). The objective is to standardize the methods used and to make best use of the MERMOS method, by adapting it to meet the engineering constraints associated with the analyses for Human Reliability Evaluation. This paper presents the initial defined stages of the methodology, and the principles on which this section of the work is based.