Critical heat flux study on WWER-1000 fuel rod assembly models

Experimental results of a heat transfer crisis study are presented. The experiments were conducted an a 7-rods cluster with uniform power density distribution both across the radius and length of the cluster. The coolant pressure has been varied from 15.5 up to 18.0 MPa and the mass flow rate from 2400 up to 3800 kg/m2s. The cluster consisted of 7 electrically heated rods with 9.0 mm diameter. In the rod tops channels of 3.0 mm diameter and 45 mm length had been drilled for placing thermocouples that were used for registering the moment of heat transfer crisis onset. The rod pitch in the lattice was 13 mm, the cluster cross-section was 646 mm2 with hydraulic diameter of 8.11 mm, thermal diameter of 13.04 mm, the heated section length of 3500 mm and the total cluster length of 6450 mm. The experiments have been carried out on Large water test facility at SHKODA Power engineering plant (Plsen', Czechoslovakia). The thermal parameter ranges and the model geometry corresponded to those of WWER-1000 reactor. The obtained experimental data are compared with calculated ones. The systematic mean arithmetic error for an experimental series was 23.9%. The thermal load variations during crisis onset revealed by the temperature jumps did not exceed 3.47% and were of not so clearly expressed systematic nature