Thermoelastic bowing of composite cylindrical fuel rods

Abstract

The thermoelastic bowing of axially unrestrained nuclear fuel rods due to a transversely linear internal heat generation rate is investigated. The problem consists of first determining the steady-state, two dimensional temperature distribution in the circular cross section of the rod and then solving for the corresponding stresses and displacements. The thermoelastic problem is solved with the aid of the Airy stress function. For constant material properties the problem is solved exactly. For temperature-dependent material properties, an approximate method is used, with the fuel rod replaced by a number of concentric layers, each assumed to have constant material properties. Solution given by the approximate method is in the form of the infinite series. The axial stress produces a resultant moment when integrated over the cross section of the rod. Two numerical examples are solved. In the first a rod with constant properties is analyzed by both the exact and the approximate methods. The excellent agreement between the results serves to determine the validity of the approximate method. The second numerical example deals with a rod with typical variable material properties, which can be analyzed only by the approximate method.