High Cycle Thermal Fatigue damage prediction in mixing zones of nuclear power plants: Engineering issues illustrated on the FATHER case

Nuclear power plant piping may be submitted to High Cycle Thermal Fatigue phenomenon in mixing zones. French nuclear engineers have at their disposal a simplified approach for assessing the sensibility of the areas with regard to this kind of damage. The engineering tools are quite complex since they involve multi-disciplinary physic phenomena: thermal-hydraulics, mechanics and materials. The results are only qualitative and globally conservative, and this method is only used to identify and to classify the mixing zones which could present a risk. In this framework, this paper proposes to perform a more realistic application of this engineering method on the particular case of the FATHER experiment. The idea is to compare the numerical prediction results with the expertises performed on the FATHER mock-up. Some generic engineering issues raised by nuclear fatigue analyses are here illustrated by the sensitivity analyses which have been performed. The determination of the fatigue loading and the choice of the material criterion are particularly discussed since they are very significant parameters in the analysis.