Evaluation of critical heat flux and flooding experiments for high conversion PWRs

High converting PWR's (HCPWR or APWR) are based on fuel elements with rod placed in a tight lattice triangular array. The critical heat flux (CHF) correlation developed at KfK for such geometry has been tested against recently performed experiments. For tests with grid spacers the correlation has been confirmed by various experiments within a scatter band of 10-20%. The original KFK correlation prediction for spiral supports is based on tests with single spiral wire and it is not applicable for six integral spiral rib supports. A modification of the correlation, which accounts for this kind of support as well, is proposed in the paper. The computer code FLUT originally developed at GRS-Garching, for the modelling of the flooding phase during a Loss-of-Coolant Accident in a PWR, has been modified to account for the different APWR core geometry. The new version of the code developed at KfK is able to predict better than FLUT both the tests performed for the APWR as well as for the PWR core geometry. The latest version of FLUT-FDWR, called FLUT-FDWR-MM, allows a finer axial nodalisation of the fuel rod in the region of the quench front. This reduces the oscillations in the rod cladding temperatures and in other physical parameters, and, in some cases improves even the level of the code predictions. (author). 38 refs, 14 figs, 6 tabs