Validity of calculation methods for leakage rates from cracks

The statistical evaluation of the deviations between the calculated results of five leakage rate models and the measured leakage rate values determined in real and simulated cracks using water/steam showed that acceptable prediction accuracy (leak-before-break behavior) can be obtained only on some or one's own measured values. At present, there is thus no generally valid hot water leakage rate calculation method applicable to all crack configurations and crack wall roughnesses described in the literature. Extrapolation of the leakage rate models to other systems of substances (typical in chemistry) is therefore not yet possible with certainty. The altogether best accuracy of reproduction has so far been obtained with the leakage rate model developed by the Karlsruhe Nuclear Research Centre. The failure of the leakage rate model is attributed to the unsatisfactorily accurate description of the pressure drop across the crack. The investigations showed that with a knowledge of the actual pressure drop in liquid flow the calculation concept by P. Pana for the (critical) mass flow density is a model then permitting good reproduction of the leakage rates from cracks. (orig./HP)