Generally, fuel rods of nuclear reactors consist of a metalic alloy tube containing oxide fuel pellets. Fuel elements are formed by fuel rods disposed in bundles. In the present work, an irradication, thermal and mechanical analyses of cylindrical fuel rods are performed. A model considering thermal difusion theory, superficial difusion and vapor transport mechanisms is utilized on the determination of the irradiation swelling. Gas bubbles motion is taken into this calculation. The average gas pressure is computed. A computer program, NITSA, is developed for simulation of a reactor fuel rod performace, including temperature distributions, stress and strain calculations.