Radiation and creep analysis of strains and stresses in annular fuel elements

A theoretical analysis for the determination of strains and stresses produced in long, annular reactor fuel elements is presented. In the analysis, primary effects of thermal-cycling growth, irradiation growth, swelling, creep and neutron flux levels developed in the fuel material are taken into account.

An exact solution based on a product of the modified Bessel functions and the Fourier cosine function, and a simplified, approximate solution of the parabolic function for thermal neutron flux distribution are obtained from the simple diffusion equations. After the rate of volumetric heat generation has been determined, the radial temperature distribution in the fuel is found by using Poisson's equation of heat conduction.

From some basic assumptions the fundamental equations of displacement-strain relations, compatibility, incompressibility, equilibrium, and yield criterion are established. The strain and stress equations for the fuel elements are derived. From the calculated results of an illustrative example, the neutron flux levels, degree of thermal and radiation dilatation, thickness and properties of the cladding material are found to have important effects on the strain and stress distributions produced in the fuel elements.