State of Development in Experimental and Numerical Stress Analysis of Type CASTOR® Packages under Accident Conditions

For packages of the CASTOR® type, according to the requirements of IAEA, the mechanical integrity for 9-m drop tests under accident conditions has to be verified. In order to reduce the loads acting on the package during the tests, the package is equipped with impact limiters. To determine the loads occurring under drop test conditions, either experiments or numerical calculations can be carried out. Due to the complexness of the stress state and of the verification of results, in practice both methods are generally used for stress/strain analysis and verification. From this, the requirements for numerical calculation models are obvious. The models should have the ability to describe the short-term dynamical behaviour of packages caskcomprehensively and, as well, for various drop orientations and temperatures in such a way that local stresses can be quantified and thereby assessed. One difficulty in this sense exists in the general description of behaviour of the material wood which is used for the absorption of drop energy within the impact limiters of type CASTOR® packages. Therefore, the present established and approved state in mechanical design of type CASTOR® packages at Gesellschaft für Nuklear-Service mbH is to describe the mechanical behaviour of wood by means of an energetic calculation approach. Perspectively, it is intended to replace this practice by a dynamical calculation approach which meets the requirements described before. For this purpose, the verification of appropriate numerical calculation models on the basis of drop tests, that is to say the quantified comparison of experimentally and numerically determined stresses respectively strains, is obligatory. In this paper, the state of development, as well as the approach to establish dynamical calculation models, is pointed out. For this purpose, the dynamical calculation model of a type CASTOR® package is presented and the results determined by calculation of drop tests are compared with the results determined experimentally. On the basis of the results it is shown that the dynamical calculation model presented is suited for the determination of the temporal and spatial stress state of the whole package for different drop orientations