TIMES: Application of a Local Approach Model Within a Case Study

During the last decades the research within the field of local approach (LA) models lead to an increase of the predictive capabilities of these models and thus extended the range of applicability. Since these LA models were originally developed for cleavage fracture, they had to be adopted to account also for ductile fracture events in order to assess fracture behavior in the ductile-to-brittle transition (DBT) region. This article presents a case study, where a recently developed and validated LA model is applied to predict failure of a RPV under a realistic transient loading situation. Within this case study a loss of coolant accident is considered, where a postulated subclad flaw with 20mm depth in the nozzle corner is examined. Because the RPV steel in the nozzle corner region is ductile during a LOCA event, no failure would be predicted using original material properties. Therefore the base metal is simulated using unrealistic high embrittled material properties, i.e. irradiated at a fluence of 3.5E19n/cm² and an irradiation temperature of T_IRR = 150°C., which is to be a very conservative material condition. The reason to use this conservative material condition is to obtain a large shift in transition temperature and the necessary brittle material condition to allow the application of the LA model. The outcome of the LA simulation is compared to other constraint correction methods, like the T-Stress correction. It can be stated that: • the conventional method, which uses no constraint corrections, leads to very conservative results. • T-Stress and T₀-corrections are less conservative than the conventional method. • the prediction results attained by means of the LA model describes the failure behavior well; a large safety margin between the different concepts can be shown.