WWER-1000 reactors surveillance programmes

Typical containers for WWER standard surveillance programmes in WWER-440A/-213 reactor. Dimensions in mm. 

Abstract This chapter describes the embrittlement processes in WWER reactor pressure vessel (RPV) materials during operation - radiation embrittlement and thermal ageing. Current trend curves for both types of WWER RPV materials are given and explained. Surveillance specimen programmes are shown, as their results are used for RPV integrity and lifetime evaluation. Finally, anneahng of the RPV is proposed as the most efficient mitigation measure. 

For plants under construction, a modification of the surveillance programme is considered. Specimen containers will be located in positions representative of vessel wall conditions at Temelin NPP. Based on the fracture mechanics analysis, it was recommended to heat up the accumulator water to 5S°C and to prevent injection of ECCS water with temperatures below 20°C for all the plants. The use of low leakage core loading patterns in WWER-1000 reactors would reduce RPV wall fluence by approximately 30%. It was planned to introduce partial low leakage loading patterns at some plants during 1994 (fuel assemblies with high bumup to be placed at the core periphery). 

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