A New Approach to Calculating Fuel Temperature in TRIGA Mark I Research Reactors

Abstract

Often a forced convection heat transfer coefficient is used to calculate the peak fuel temperature for a rectangular lattice TRIGA core even though the core is cooled by natural convection. The arguments for applying a forced convection empirical relationship are examined and another relationship is suggested. The peak fuel temperature was calculated using two different correlations, Dittus-Boelter and natural convection, for pool temperatures of 30°C and 60°C. The Dittus-Boelter correlation predicted a fuel temperature rise of 1.85°C for this difference in pool temperature, contrary to the predicted rise of 25.64°C from natural convection relationships. Experimental data shows that the relationship of fuel temperature rise with increasing pool temperature is more accurately represented by the natural convection correlation than with Dittus-Boelter. Using a derived natural convection correlation, the calculated peak fuel temperatures then closely match measured data. A procedure was developed to access convective heat transfer coefficient changes in the cladding gap as a function of reactor power for the hot channel which are similar to those presented in literature.