Mastering the release of corrosion products by the passivation of steam generator tubes

The abatement of the radioactivity of PWRs primary circuit, and in particular the 58Co activity, imposes to reduce the source term, i.e. the release of corrosion products by steam generator tubes. Thanks to an improvement in the fabrication of these tubes, a better behaviour of their material has been observed both on site and at the laboratory. One mean to diminish more this source term is the passivation of the tubes before their use. Existing research works are reviewed. Passivation can be done even during the fabrication of the tubes or directly on-site before the start-up of a new reactor or after the replacement of a steam generator. The difference of efficiency in the preconditioning treatment depends on the available time for its implementation: more time is available before a reactor start-up than after a steam generator replacement. Based of EDF's experience feedback, some studies are in progress which concern the optimized preconditioning of steam generators after their replacement, some conditions being imposed by the operator (boron content and available time). Following the positive experience feedback of Sizewell B reactor, new passivation studies are also in progress at Areva and EDF about a similar but optimized passivation treatment. (J.S.)