Radiological consequences of design basis accidents for French PWRS - some IRSN views

The radiological consequences of Design Basis Accidents (DBA) were evaluated in the first safety reports of French Pressurized Water Reactors (PWR), but only some DBA have been accounted for and disparate rules and assumptions have been adopted in the calculations. Since the 90's, EDF (the French utility) and IRSN (the French TSO - Technical Safety Organisation - for the Safety Authority) have joined continuous efforts to define the radiological requirements, rules, methods and assumptions for the analyses. A standard for radiological consequences assessment was issued in 2004 by EDF based on a conservative approach to assess the radioactive releases outside the containment buildings and on a realistic methodology to evaluate their impact on the population and on the environment. The IRSN review of this standard has been achieved in 2006 and the main conclusions have been used for the radiological consequences analyses performed for the 3. periodic review of the 900 MWe reactors and the 1. periodic review of the 1450 MWe reactors. A second IRSN review based on the update of this standard has been achieved in 2009 for its application during the 3. periodic review of the 1300 MWe reactors and for the EPR safety report. The paper summarizes the current situation in regards to the radiological requirements, the general approach and the main rules to evaluate the radiological consequences of DBA. Moreover, it presents some outcomes of the work, including both suggestions for plant improvements and detection of the needs for future research. To illustrate these points, two examples of DBA are provided: Steam Generator Tube Rupture and Loss Of Coolant Accident. The final part of the paper provides the IRSN's vision for future, when reactors belonging to the Gen III (EPR) and Gen II (current PWRs) generations will be in simultaneous operation in France, as a consequence of the plant life extension underway. The design requirements regarding the amplitude of hypothetical release in case of accident are highly more ambitious for the EPR and justify, for IRSN, future works to improve the situation for Gen II reactors, for both DBA and severe accidents. (authors)