Prediction of shallow water phenomena with reactor safety codes

The codes used to predict transient hydraulic phenomena in nuclear reactors use phasic averaged equations of motion. In horizontal flows these are equivalent to shallow water theory, and the codes should be able to predict the standard results of this theory. Taking dam breaks and Kelvin-Helmholtz instability as examples, it will be demonstrated that this is indeed so. However, the conditions or the successful reproduction of the theoretical results are sometimes arduous, and may not be met in reactor calculations. (author)