Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

In the Research Centre Rossendorf pre- and posttest calculations to the OECD/NEA/CSNI International Standard Problem No. 33 were carried out with the GRS code ATHLET. This Problem was a natural circulation experiment with stepwise reduced primary coolant inventory. In the ATHLET calculations after a drainage of about 50% of the primary inventory cyclic oscillations of the mass flows and the void fractions were observed. These are found in the experimental results also. A simple analytical model was developed to distinguish physically caused oscillations from numerically caused ones. The oscillations observed could be interpreted as density wave instability in the local recirculation loop core- bypass.