The regulatory compliance of the containment system is of essential importance for the design assessment of Type B(U) transport packages. The requirements of the IAEA regulations SSR-6 for accident conditions of transport implies high load on the containment system. The integrity of the containment system has to be ensured under the mechanical and thermal tests. The containment system of German transport packages for spent nuclear fuel (SNF) and high level waste (HLW) usually includes bolted

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... s with metal gaskets. BAM Federal Institute for Materials Research and Testing as the German competent authority for the mechanical and thermal design assessment of approved transport packages has developed the guideline BAM-GGR 012 for the analysis of bolted lid and trunnion systems. According to this guideline the finite element (FE) method is recommended for the calculations. FE analyses provide more accurate and detailed information about loading and deformation of such kind of structures. The results allow the strength assessment of the lid and bolts as well as the evaluation of relative displacements between the lid and the cask body in the area of the gasket groove. This paper discusses aspects concerning FE simulation of lid systems for SNF and HLW transport packages. The work is based on the experiences of BAM within safety assessment procedures. The closure system of a generic cask is modeled to analyze its behavior under the mechanical load complying with IAEA regulatory accident conditions of transport. The issues considered include modeling strategies, analysis techniques and the interpretation of results. GENERAL ASPECTS OF NUMERICAL ASSESSMENT OF LID SYSTEM Type B(U) packages for transport of spent nuclear fuel (SNF) and high level waste (HLW) mostly consist of thick-walled cylindrical shells with plane bottoms. The containment of Type B(U) packages used in Germany for transport and interim storage is closed by two bolted lids (primary and secondary lid) * . According to IAEA regulations SSR-6 [1] the containment system has to fulfill the activity release criteria under specified routine, normal and accident conditions of transport (RCT, NCT and * Double barrier system is implemented in Germany due to interim storage requirements. Only one barrier is necessary for the transport condition.