Analysis of some ways of taking into account the radially non-uniform power density effects on heat transfer crisis

Some ways of taking into account the radially non-uniform power density effects in the heat transfer crisis margin calculations are considered. The different approaches are evaluated by comparison with experimental data on heat transfer crisis in fuel rod bundles with high power density radial non-uniformity. Calculations with the use of subchannel method have been performed on VEVERKA code. From the obtained results the following conclusions can be drawn: the method of one-dimensional optimistic estimate on the averaged over the bundle cross-section coolant parameters is not applicable to the rod bundles with high power density radial non-uniformity; to improve the calculation reliability some more accurate correlation for the turbulent mixing coefficient is needed as well as the basing of the bundle cross-section breaking into subchannels; a good agreement with experimental data has been obtained from the one-dimensional mean estimate; for the rod bundles with the highest power density radial non-uniformity the arithmetical mean error in the critical power level calculation was about several per cent