The Analysis of Relaxation of the Contact Force Between the Fuel Rod and Spacer Grid in the Vver Fuel Assembly

Fuel rods and spacer grids form a rigid frame of the VVER fuel assembly (FA). The FA stiffness is ensured by welding quality of the spacer grid and the guide tubes, as well as tight fitting of the fuel rods in the spacer grids. During the operation, the stiffness of the fuel assembly decreases, and its structure becomes distorted. This has a negative effect on the operation of the nuclear core. The main reason for the distortion is the relaxation processes between the fuel rods and the spacer grids as the contact forces between them decrease over time. Currently, the relaxation process of the contact interaction between the fuel rod and the spacer grid under real operational loadings is not sufficiently studied. The present work researches the relaxation process of the contact interaction depending on high temperature, neutron irradiation, axial force acting upon the fuel rods, and friction between the fuel rods and the spacer grids. The results obtained make a significant contribution to the study of deformation processes in the fuel assemblies and the nuclear core as a whole.

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