Recent innovations in the methodology for breeder reactor risk assessment

The model developed for probabilistic analysis of liquid metal reactor risks has three stages of event trees: system response, core response and containment response. The chapter summarizes important aspects of the philosophical foundation for liquid metal reactor probabilistic risk assessment methodology. These are: probability is interpreted as 'degree of belief', risk is characterized in terms of event probabilities, rather than event frequencies, and probabilities that are input to the probabilistic risk assessment model are 'assigned' rather than 'estimated' or 'predicted'. These principles have been consistently applied to evaluations of all three stages of event trees. The basis for all the probability assignments in the procedures discussed are made visible and reviewable. Thus, the user of the assessment can develop confidence in the results and be willing to accept their influence of his decisions. (author)