Transient thermal stresses in liquid metal cooled reactor fuel elements

Abstract

A numerical solution for two-dimensional transient thermal stresses in a liquid metal cooled nuclear reactor fuel element is presented. The method consists of first determining the two-dimensional transient temperature field across a fuel element and its adjacent coolant channel by a finite difference solution to a set of partial differential equations for a given time variation of both reactor power and coolant flow rate. The determination of the temperature field solution takes into account a heat source term and conduction in the fuel element in the direction perpendicular to the direction of coolant flow, convection and conduction perpendicular to the coolant flow in the coolant channel, and convection only in the direction of coolant flow in the channel. After the transient temperature field is determined, values of the components of the stress tensor are calculated using a variational type solution to an inhomogeneous biharmonic equation for the Airy stress function in uncoupled, linear, quasi-static thermoelastic theory. Results are presented for temperatures and thermal stresses in plate and cylindrical fuel elements for a variety of power level and coolant flow transients, including the loss of pumping power accident. The computer programs which were used to calculate these results are also included.