Probabilistic analysis of operators actions at the ignalina nuclear power plant taking account of the specific conditions of accident sequences

The procedure used at the Ignalina nuclear power plant for probabilistic analysis of the actions taken using the ASEP and THERP methods by operators during accidents is described. The method makes it possible to evaluate the probability of operator error at different stages of the action taken – identification, making a decision, and taking action – as well as correctly taking account of different factors influencing human actions – emergency signaling, instrument indications, presence of instructions, preparation and experience, stress, time, and others. The procedure used in the qualitative and quantitative analysis is briefly reviewed and examples of the evaluation of real actions taken by operators are given. It is shown that it is important to take account of the specific nature of the development of an accident when evaluating the probabilities of operator error.