Methodological Aspects for Numerical Analysis of Lid Systems for SNF and HLW Transport Packages

Abstract

The regulatory compliance of the containment system is of essential importance for the design assessment of transport packages for radioactive materials. The requirements of the IAEA transport regulations SSR-6 for accident conditions implies high load on the containment system of Type B(U) packages. 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 lids 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 issues considered are the assessment methods used in the BAM-GGR 012 for bolted lid systems along with the nominal stress concept which is applied for bolts according to that guideline. Additionally, modeling strategies, analysis techniques and the interpretation of the results are illustrated by the example of a generalized bolted lid systems under selected accident conditions of transport.

Numerical Approach for Containment Assessment of Transport Packages Under Regulatory Thermal Test Conditions

“…There is a considerable scatter in the bolt pretension by an appointed torque because of the dispersion of friction conditions at the threads and under the bolt heads as well as an imprecise bolt tightening technique. A model with primary lid (PL) geometry with bolts of strength class 8.8 having the minimum pretension in accordance with BAM criteria [6] was considered as the basis configuration for calculation in this paper.…”

“…All these contacts are established in the initial step. For the gasket there are different kinds of interface conditions: connection to the lid by a tied contact 6 and a separable contact with the cask flange. The gasket's torus diameter is 1 mm larger than the depth of the groove.…”