Reactor pressure vessel surveillance programmes of the Spanish NPPs

Reactor pressure vessel Surveillance Programmes are implemented in nuclear plants in order to monitor the changes in the mechanical properties of the vessel steels and welds. Basically, such a programme consists of tracking the RPV integrity through an experimental checking of the vessel materials behaviour against the neutron irradiation (embrittlement), based on the analysis of a series of irradiated capsules containing specimens for subsequent mechanical testing, along with temperature and neutron flux monitors, the aim being to determine the evolution of the mechanical properties of the RPV materials. The paper summarizes the main characteristics and the status of the Surveillance Programmes of the Spanish PWR and BWR reactors, including a description of the standard and requirements applying in Spain to the RPV surveillance programmes. After describing the process and contents of the surveillance programmes (materials considered, number of capsules and their drawing timing, type of specimen, testing, etc), a summary of the main experimental results (RTNTD, USE) obtained up to now are presented. The results obtained from the irradiated specimen tests show coherent data and predictions ensuring compliance with the limits and requirements established in the standards. It is generally concluded that the fracture toughness will not be a concern for Spanish NPP vessels throughout their service lifetime. (Author)