Reference temperature determination of RPV steel using small-sized fracture toughness specimens

The efficiency of the Master-Curve reference temperature (MCRT) determination for Reactor Pressure Vessel (RPV) material using three-point bending half-thick SE(B) and compact tension C(T)0.16T specimens is analysed. The designed and manufactured experimental equipment for fracture toughness (FT) testing at cryogenic temperatures is described. For specimen cooling the liquid nitrogen and its vapours were used. Specimen pre-cracking was performed according to ASTM E647 standard, FT testing, and data treatment – in accordance with ASTM E399 and ASTM E1921. The experiments were carried-out on the specimens produced from two WWER-1000 RPV forgings made of 15Kh2NMFAA steel in initial (unirradiated) state. The experimental data were processed using the Master Curve methodology. It is shown that the as old USSR’s PNAE G-7-002-86 design FT curve as well as modern Ukrainian SOU NAEK 177:2023 and EU’s VERLIFE curves, are too conservative relatively to the obtained Master Curves.