A transient heat conduction model for reactor fuel elements

Abstract

A two region, lumped-parameter model is developed for the treatment of thermal transients in reactor fuel elements. The fuel-region heat condution is treated by a fundamental mode approximation to the time-dependent Green's function. The model also accounts for the thermal resistance of the fuel-cladding gap and the cladding-coolant interface, and for the non-negligible heat capacity of both the fuel and cladding regions. The thermal resistance of the cladding is neglected. The resulting differential equations are similar to those that are obtained were the lumped-parameter model of Tong. The results from the fundamental mode model and the Tong model are compared to exact analytical results that are obtained for a number of highly idealized problems. The fundamental mode model is then used to treat a series of highly idealized loss-of-coolant transients. The fundamental mode model has been incorporated into the FLASH-2 code to treat more realistic accident transients.