MECHANICAL DESIGN ASSESSMENT APPROACHES OF ACTUAL SPENT FUEL AND HLW TRANSPORT PACKAGE DESIGNS

In recent years BAM finalized the competent authority assessment of the mechanical and thermal package design in several German approval procedures of new spent fuel and HLW package designs. The combination of computational methods and experimental investigations in conjunction with materials and cask components testing is the most common approach to mechanical safety assessment. The methodology in the field of safety analysis, including associated assessment criteria and procedures, has evolved rapidly over the last years. New features relating to analysis aspects and assessment methodologies are summarized in this paper. The design safety analysis must be based on a clear and comprehensive safety evaluation concept, including defined assessment criteria and constructional safety goals. In general, for new package designs the implementation of experimental package drop tests in the approval process should be obligatory. Additionally, pre- and post-test calculations as well as components or material testing could be important. The extent to which drop tests are necessary depends on the individual package construction, the materials used and identified safety margins in the design. Numerical calculations by means of the Finite-Element method are part of safety analysis concepts of different package design approvals. The calculations are carried out statically or dynamically depending on the particular loading situation (static load or impact) and material behavior (e.g. strain rate dependency). The use of an appropriate small-scale or a full-scale test model determines the extent and depth of the correlated calculations. Exact calculations require an input of realistic material laws which often have to be generated by appropriate material testing. This paper concentrates on the complex relationship between the chosen drop test program with a small scale model and related mechanical Finite-Element analysis for design verification. As an example this paper describes a specific new German dual purpose cask design developed for transport of vitrified high-level waste from France to interim storage in Germany.