Validity of the master curve temperature dependence assumption for highly embrittled RPV materials; Results from the IAEA Coordinated Research Project (CRP-8)

Planman, T.*; Onizawa, Kunio ; Server, W.*

The fracture toughness transition curve shape in the Master Curve (MC) has been discussed since the original empirical definition of the curve in 1991. In most cases the standard MC approach, assuming a constant transition curve shape, has proven to give a realistic description for also highly irradiated ferritic steels. The fracture toughness data collected and analysed in the IAEA CRP-8 Topic Area 3 supports the validity of the curve shape assumption of ASTM E1921 also in case of irradiated steels and gives no rise to change the present definition. The Master Curve C-parameter (the shape parameter) estimation is proposed as an appropriate analysis method when there is need to estimate also the temperature dependence, whereas the SINTAP procedure is recommended for ensuring conservative lower bound estimates when material in homogeneity is suspected. The results show that irradiation may slightly lower the fracture toughness in the upper transition region in relation to that predicted by E1921, but the effect after moderate T0 shift values seems to be negligible.