Common cause failures: identification and quantification

In the context of Probabilistic Safety Analysis (PSA), treatment of Common Cause Failures (CCFs) may have critical influence on the credibility of the studies, on the question of completeness and on interpretation of results. A Nordic project 'Risk analysis', initiated in 1985, has among its main objectives to perform in-depth studies of dependent failures and human interactions, and generally to investigate assumptions and limitations of current PSAs. During the first phase of the project the activities concentrated on performing a Benchmark Exercise (BE) concerning CCF-data. Preliminary results of the exercise are presented in this report. The main findings concern both procedures for search for CCFs, use of classification systems, and quantification of CCF-contributions by means of direct assessment and use of parametric models