Extended analysis of VVER-1000 surveillance data

Up to now 20 surveillance specimen sets of 14 VVER-1000 Reactor Pressure Vessel (RPV) have been evaluated in Russia, Ukraine and Bulgaria by different testing organisations: • Kurchatov Institute, Russia (10 RPVs); • Institute for Nuclear Research, Ukraine (two RPVs); • Institute of Metal Science, Bulgaria (two RPVs). The extended analysis presented here is based on the results of 17 surveillance sets testing results of surveillance programmes. The materials involved contain very low and homogeneous levels of phosphorus and copper and a significant variation of nickel and other elements like manganese, etc. The observed temperature transition shifts are showing consistent behaviour: • The steels with low nickel content are embrittling at a much lower rate than the one predicted by the Guide (chemistry factor=20). • The Guide looks to be conservative also for the higher nickel steels if the content of manganese is lower than 0.8 wt%. • The steels embrittling at much higher rates are those with high nickel and high manganese contents at the same time. The threshold for nickel is evaluated to be at Ni>1.5 wt% and for manganese at Mn>0.8 wt%. Manganese, together with nickel, seems to play a key role in low Cu and P steels embrittlement [1,2]. Correlation analysis which considers Ni and Mn and fluence dependence to 1/3 power are showing predictive capabilities within 20 °C scatter band in most cases. Other elements, like, for example, carbon and sulphur could also explain the residual scatter in the data [3].