Development of pad element for core deformation analysis. Formulation of pad element

It is important to understand the deformation behaviors of FBR core in the aspects of safety and economy, i.e., the reaction change in the transient period, the fuel life expectation, and the removal of subassemblies. Furthermore, the realization of precise analysis of the core deformation behaviors will contribute to sophistication of the core structure design. The aim of this study is to develop a special 'PAD ELEMENT' which owes the role to treat the interaction between subassemblies at their pads precisely. This specified element consists of 6 ordinary beam elements, which are spokelike arranged in order to express various characteristics of the pad of a subassembly. In this report, the detailed formulation of the 'PAD ELEMENT' and the result of its fundamental test calculation are described. If we use shell elements for modeling of wrapper tubes in order to analyze the core deformation behavior more precisely than that by beam elements, we will face a difficulty in implementing numerical calculation. However, this pad element promises practical core deformation analyses because this element is consistent in the modeling by beam elements. The gists are as follows. (1) PAD ELEMENT is proposed in order to improve the accuracy of core deformation analyses. This element possesses the functions of the flexibility of pad cross section including coupling effect, bending or torsional moment caused by friction forces between pads and uniform cross sectional deformation at pads such as thermal expansion, swelling, etc. (2) The functions and the behaviors of PAD ELEMENT are verified by applying this element to some fundamental problems. The perspective is obtained that the characteristics at pads can be easily considered by adopting PAD ELEMENT to conventional analysis model by beam elements. (author)