PSA data updating in France

In 1990, the French Institute for Nuclear Safety and Protection (IPSN), carried out a Level 1 -PSA for the 900 MWe series PWRs. At the same time, the French licensee, Electricite De France (EDF), carried out an equivalent study for 1300 MWe series reactors. Thanks to the standardisation of the French nuclear power plants (56 PWR units in three series) which are run by a single licensee, it is possible to obtain statistical data which are representative of all reactors in the same series. In the 1990's PSA, the data were assessed considering the experience feedback between 1983 and 1986, regarding equipment reliability, initiating events, operating profiles and common modes. In 1996, EDF undertook to update these studies in the light of accumulated operating experience. IPSN carried out a critical analysis of the reassessment methods, and validated the most safety significant data sets. This work has provided a common referential. 'Frequent' initiating events (observed at least once in France) were calculated on the basis of French experience feedback. 'Rare' initiating events (never observed in France) were calculated on the basis of world-wide PWR experience feedback, where such information could be used. When none of these methods seemed realistic, expert appraisal was used. As regards the 900 MWe and 1300 MWe series' operating profile, EDF now has a statistical application which collects all the periods spent in the different standard states as well as the number of transients to each state. Supplementary data were needed to establish the profile during outages. To gather the new 900 MWe series equipment reliability data, equipment considered to be 'safety sensitive' was selected to be dealt with first on the basis of French experience feedback from 1988 to 1993. The main points of the method are choice of representative samples, validation of information provided by databases, determination of failures criticality and consideration of corrective actions carried out on the equipment. During 1998, EDF and the IPSN will undertake to update the reliability data for the 1300 MWe series. This updating will provide the opportunity to confirm some of the methodological principles used for the 900 MWe data, or to introduce new concepts. (authors)