Fuel cladding mechanical interaction, (1)

Elastic-plastic analysis was made to evaluate the strain distribution in a cladding tube made of austenic stainless steel by the finite element method. An assumption was made for the deformation process of fuel and a cladding tube that the pellets with cracks swell radially and cause the expansion of the cladding tube. The calculation model of the fuel and the finite element layout are shown by figures. Two models of fuel radial cracks, i.e. 8 cracks with the angle of 7.2 deg and 6 cracks with the angle of 10.0 deg. were analyzed. The radius of central void was assumed to be 0.95 mm. The results of analysis are summarized as follows: (1) the plastic region occurs at first on the inner surface of a cladding tube facing the cracks of pellets and then spreads outward. (2) The circumferential stress induced in the cladding tube is higher on the inner surface than on the outer surface (3) When the friction coefficient between fuel and the cladding tube is infinite, the strain concentration is limited to the region facing the cracks of pellets. (Aoki, K.)