Approximation of mean fuel temperatures in WWER-1000 core

Program PIN was used to calculate the coefficient of heat transfer through the fuel-cladding gap, and the temperature fields in the fuel element in the WWER-1000 core. From the results, approximate dependences were obtained of mean fuel temperatures on the local linear power output of the fuel element in the core. The mean fuel temperatures were averaged along the pellet diameter. The aproximation polynomial was of the fifth degree, the results are tabulated and shown graphically. Similar to fuel elements in the WWER-440 core, ambiguity was observed of the relation between linear power output and the mean fuel temperature. The deviations for different axial sections of the same fuel element reached as much as 140 degC for the same linear output value. The best results were obtained for fresh fuel. Different models can be selected in the PIN program for burning-up fuel; the mean fuel temperature markedly depends on the selection. The results presented have thus only an informative nature. It is stated that the description of temperature fields in fuel should be rendered more specific, that results should experimentally be tested, etc. (Z.M.). 4 figs., 4 tabs., 10 refs