Working session 5: Operational aspects and risk analysis

A general observation is that both operational aspects and risk analysis cannot be adequately discussed without information presented in other sessions. Some overlap of conclusions and recommendations is therefore to be expected. Further, it was assumed that recommendations concerning improvements in some related topics were generated by other sessions and are not repeated here. These include: (1) Knowledge on degradation mechanisms (initiation, progression, and failure). (2) Modeling of degradation (initiation, progression, and failure). (3) Capabilities of NDE methods. (4) Preventive maintenance and repair. One should note here, however, that all of these directly affect both operational and risk aspects of affected plants. A list of conclusions and recommendations is based on available presentations and discussions addressing risk and operational experience. The authors aimed at reaching as broad a consensus as possible. It should be noted here that there is no strict delineation between operational and safety aspects of degradation of steam generator tubes. This is caused by different risk perceptions in different countries/societies. The conclusions and recommendations were divided into four broad groups: human reliability; leakage monitoring; risk impact; and consequence assessment