Structual analysis of subassembly wrapper tubes with three-dimensional finite element code KASTEN

A mathematical model of the structural properties of a fuel element under in-pile conditions has to incorporate the wrapper tube, the fuel pins and the spacing devices between them. The finite element method is one way to build such a model because by that it is possible to connect bodies which are as different in shape as the wrapper tube, spacer grids and pins. Despite their different shapes they all may be build out of flat or curved plate elements. The first step in reaching this aim may be the code KASTEN which simulates the mechanical properties of either the wrapper tube or the fuel pin cladding. The code calculates the thermal and neutron swelling strains and the resulting displacements and stresses. The creep strains are calculated iteratively for each time step. External forces induced by pressure, fixed or flexible supports are taken into account and may be changed during the irradiation time. The code has been used to investigate the behavior of pins and wrapper tubes in the planned KNK-II carbide element under various loading conditions and with differential swelling formulas. The result are compared with results of another code and are in good agreement. (Auth.)