Open issues in PTS assessment of WWER RPVs

Abstract

The main aim of the paper is the critical review of the current methodologies of WWER RPV brittle fracture assessment from the practical point of view. Design rules PNAE-G-7-002-86 and three modern approaches (Ukrainian MT-D.0.03.391-09, Czech and EU VERLIFE and Russian MRKR-SKhR-2004) are considered. Main issues of the modern methodologies are divided into two parts, that are related to computational fracture mechanics and to fracture characteristics (Fracture Toughness curve and Ductile to Brittle Transition Temperature) of metal of RPV beltline zone as well.The misconceptions of current methodologies of RPV brittle fracture assessment are described as well as recommendations for they improvements are given. It is shown, that some of problems (for instance cladding integrity, modelling of weld residual stresses, Fracture Toughness curve modification) needs to be justificated, before they are considered as a part of good-practice methodology of RPV integrity assessment. In particular, unreasonable high level of conservatism of Fracture Toughness curves specified in modern methodologies is shown. And finally, for some of them such as VERLIFE’s probabilistic embrittlement trend curve generation and Master-Curve approach for both deterministic and probabilistic assessment, – engineering inapplicability is demonstrated. Some improvements, such as chemical factor consideration and transition temperature determination for radiation embrittlement assessment, probabilistic RPV brittle fracture assessment are developed by “IPP-Centre” LLC and briefly presented.