IRRADIATION EMBRITTLEMENT OF REACTOR PRESSURE VESSEL STEELS WITH A DIFFERENT NICKEL CONTENT

The analysis of the Ukrainian NPP surveillance test results (similar to 9 years of exposure) for the VVER-1000 reactor pressure vessel has been performed. Fracture toughness data for the RPV steels have been re-evaluated using the Master curve methodology. It is shown that the irradiation embrittlement rate for welds with a high nickel (>1,5 % wt) and high manganese (>0,8 % wt) contents is more than a normative value. Furthermore, the conclusion is made that the critical brittleness temperature shift due to irradiation, Delta T-F, may underestimate the fracture toughness curve shift. The PNAE G-7-002-86 normative approach has demonstrated to characterize highly conservatively the fracture toughness of some unirradiated RPV materials.