[en] The results of experimental research aimed to determine the maximum admissible thermal load on the inner surface of the compensation rod, flow conditions, recording the thermal-hydraulic parameters and visualization of the occurring phenomena which have been accomplished in the water test facility WIW-300, are presented in the paper. The flow parameters preceding the CHF occurrence in a vertical channel of annular geometry with 23/20 mm O/I diameters and of 1000 mm length under transient conditions were analysed. Based on the experimental investigations it was obtained an empirical correlation for the DNB and CHF occurrence in down-flow forced convection in uniformly heated tube depend on initial flow parameters. (author)