Validation of Constraint Based Methodology in Structural Integrity – VOCALIST: Analytical Programme

The aim of the EC project VOCALIST (Validation of Constraint-Based Assessment Methodology in Structural Integrity) is to develop and validate innovative procedures for assessing the level of, and possible changes to, constraint-based safety margins in ageing nuclear pressure boundary components. An iterative process of experiment and analysis will address this overall objective. The analytical investigations within VOCALIST cover all three ferritic materials used in the experimental program. Two of the three materials are investigated in the brittle to transition regime and the third material will be tested in the ductile regime. The main effort is to predict the results of the large-scale tests in terms of constraint effects. All participants use constraint based methods, which are in a first step calibrated to the behaviour of well-known specimens and then applied to the features or the large scale tests of each material. ORNL has developed a very promising method for the prediction of cleavage fracture using the local approach based on a three-parameter Weibull model. This model has been successfully used to predict the biaxial effects on fracture toughness during the HSST program. It could be further developed and used to predict the structural behaviour of a component containing a shallow flaw and loaded biaxially by using the results of standard fracture toughness specimen with deep notches and loaded uniaxially. In this contribution the first steps of the analytical program of VOCALIST are introduced. The specimens and components under investigation are highlighted with respect to modelling aspects and the first results are presented