The use of master curve method for statistical re-evaluation of surveillance test data for WWER-1000 reactor pressure vessels

Abstract

The surveillance fracture toughness test data for WWER-1000 reactor pressure vessel materials from Ukrainian nuclear power plants were re-evaluated using the Master curve methodology. It has been shown that experimental temperature dependence of fracture toughness parameters and a scatter of KJc values are in a good agreement with a Master curve shape and 5 and 95% tolerance bounds for materials in unirradiated condition and after neutron irradiation up to fluence 41. 2·1022 n/m2 (E > 0.5 MeV). For the Khmelnitsky nuclear power plant unit 1 reactor pressure vessel an analysis has shown that normative approach PNAE G-7-002-86 underestimates essentially the measured fracture toughness of unirradiated weld metal. The reference temperature T0 calculated according to the Master curve method was compared with a critical brittleness temperature TK0 for reactor pressure vessel materials in unirradiated condition. It has been found that temperature T0 is much lower than TK0 . Furthermore a difference between T0 and TK0 values varies essentially from one material to another. A correlation between temperatures T28 J defined from Charpy energy curve and T0 values calculated from precracked Charpy specimens test was obtained. The analysis has shown that the results based on precracked Charpy specimens can provide nonconservative assessment of fracture toughness for WWER-1000 reactor pressure vessel materials.