Applications of the Master Curve Approach to Irradiated Steels

The Master Curve approach is being introduced in the evaluation of the fracture toughness of low-alloy ferritic steels used in reactor pressure vessels. In comparison with ASME approach, the Master Curve methodology provides both a new definition of the reference temperature for the ductile-to-brittle transition in fracture toughness, T0, and an improved reference toughness curve. The Master Curve methodology is based on the observation that fracture toughness transition curves present a characteristic shape common to all ferritic steels. Consequently, one same Master Curve can be used for all vessel steels, changing only its position on the temperature axis until it passes through the average fracture toughness value, which is obtained from the tests performed on the material of interest. The Master Curve provides significant technical enhancements compared with the methodology currently incorporated in the ASME code. The fundamental understanding of Master Curve has been achieved, but application issues are emerging facing the integrity evaluation of reactor pressure vessels. The current situation of the Master Curve methodology is reviewed in this paper, including the last developments for WWER reactors. The open issues are discussed, and the preliminary results from investigations being carried out in Spain are presented