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The results of a reflood investigation of model VVER and PWR fuel assemblies for maximum design-basis and beyond design-basis accidents performed on the RBHT, SVD, and PARAMETR stands are presented. The variation ranges of the regime parameters are: initial temperature of fuel element 460–600°C; mass velocity of water 47–160 kg/(m2·sec), underheating at the entry into the model fuel assembly 11–108°C; pressure 0.14–0.42 MPa; and, linear heat flux density simulating the residual heat release 0–2.3 kW/m. A colligating relation describing the experimental data to within 30% is obtained for the wetting front of model fuel assemblies, which makes it possible to calculate the cool-down time of model fuel assemblies with different designs and evaluate the reflooding time of VVER and PWR.

The purpose of this work was to obtain experimental information on the temperature state of fuel elements in the transcritical region and to develop methods for calculating the heat-emission coefficient. The following region of regime parameters was investigated: pressure 11.7–16.7 MPa, temperature at the entrance into the fuel-assembly model 200–285°C, mass velocity 700–1900 kg/(m2·sec).

A new method of calculating the critical heat flux in fuel-rod assemblies is presented. The method is based on a generalization of the experimental data in tabular form. The table for the critical heat fluxes is constructed for the correct macrocells of triangular bundles with relative rod spacing s/d=1/4 and a 9.36 mm heat diameter of a microcell for the following conditions: no effect due to peripheral zones and unheated rods; turbulizing influence of the entrance conditions and spacers; and, the heating along the length and across assemblies is uniform. To use the table for other, quite wide regions of the determining parameters, relations are presented for calculating the effect of the important parameters: heating diameter, relative rod spacing in the assembly, distance to the entrance (heated length), turbulizing influence of the spacers, and others. 1 figure, 1 table, 9 references.