Upgrading of existing NPPs as regards safety requirements evolution: periodic safety reviews

In France, there are 58 operating units (900, 1300 and 1450 MWe) with a cumulated experience of about 1000 reactor x years. The Periodic Safety Review (PSR) for these units is undertaken every ten years. The generic study is relative to standardised series while the on-site conformity check concerns each specific unit. At the moment, 2 PSRs have been completed and one is under progress. The main objectives of the PSR are to check that the plant remains in conformity to its current safety referential and to assess this referential in comparison with rules applied for more recent plants (N4 series). The Probabilistic Safety Assessment (PSA) is widely used and modifications are decided only if the safety improvement is significant with regard to potential drawbacks of modifications and their cost. The decided modifications are implemented as a batch, during the ten-year outage. The results of PSR (studies and modifications) are introduced in the safety analysis report and in general operating rules in order to have a consistent documentation. The periodic Safety Review also contributes significantly to the objective of a life duration of at least forty years by maintaining the plants in compliance with stable safety requirements