The strain and stress distributions resulting from the combined effects of radiation, creep, and neutron flux levels in long externally and internally cooled tubular reactor fuel elements are determined analytically. Primary effects of thermal-cycling growth, irradiation growth, swelling, and creep of the fuel materials under operating conditions of power reactors are taken into consideration. An exact solution of the modified Bessel functions and an approximate solution (using a parabolic function) for neutron flux distribution are obtained from the simple diffusion equations. From the relation that the rate of heat generation is proportional to the neutron flux, the rate of volumetric heat generation in the fuel is found. Then the temperature distribution in the fuel is determined by using Poisson's equation of heat conduction. The equations of the displacement-strain relations, compatibility, incompressibility, stress equilibrium, yield criterion, and boundary conditions are established from some basic assumptions. The strain and stress equations for the fuel elements are derived. From the calculated results of a numerical example, the neutron flux levels, thermal and radiation dilatation, irradiation creep, thickness, and properties of the cladding material are found to have significant influences on the strain and stress distributions produced in the fuel element.