Considerations of the Competent Authority Concerning the Assessment of a Brittle Fracture Safe Ductile Cast Iron (DCI) Cask Design

Abstract

The assessment of a brittle fracture safe ductile cast iron (DCI) cask design must ensure the integrity of transport and storage casks for radioactive materials under the most damaging accident conditions. Based upon the determination of the mechanical impact behaviour and stress analysis, for cask design sufficient material properties like fracture toughness must be ensured in series cask production by accepted quality assurance measures. The current BAM safety assessment concept has been established in the 1980s and is mainly based upon approval design tests with large cylindrical CASTOR and TN casks equipped with impact limiters. This concept needs only a reduced fracture mechanics analysis because of stress limitation at a level of approximately 50% of materials yield strength and appropriate quality assurance measures which ensure only tolerable crack-like defects within the cask structure in connection with guaranteed fracture toughness down to −40°1C. In other cases a detailed fracture mechanics analysis might be necessary because of higher stress levels and cask behaviour under dynamic conditions. This paper presents actual considerations and results at BAM from drop tests with new cask designs such as cubically shaped cast iron containers and the POLLUX cask designed for transport, interim storage and final disposal of spent fuel.