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In the present study, ductile cast iron from an original DCI container with a wide variety of microstructure was
investigated in order to determine the materials fracture toughness under impact loading conditions. Three-point bending
specimens with thickness of 140 mm from a cubic DCI container were investigated at elevated loading rates to
provide reliable fracture toughness parameters for the assessment procedures. In contrast to static fracture behaviour,
the fracture toughness values of thick-walled DCI at higher loading rates show a remarkable reduction with decreasing
temperature up to 50 °C and a significant shift of the transition range. The lower bound fracture toughness value used
in the BAM DCI safety concept was confirmed for impact loading conditions by these fracture mechanics tests using
large specimens. These measurements are relevant to the licensing tests for storage containers without shock absorbers,
especially to the assessment of the dynamic behaviour of crack-like defects inside a cask structure under drop test conditions.
Using extensive dynamic numerical analyses it could be shown, that for special crack configurations the dynamic
crack tip parameter (KI, or J) may be estimated by static formulae even under mechanical impact. These results
of the safety assessment were verified according to the German Konrad repository acceptance criteria by a drop test
with a cubic waste container with artificial crack-like defects from 5 m height onto a representative storage facility
foundation.
BAM is the responsible authority in Germany for the assessment of the mechanical and thermal design safety of packages for the transport of radioactive materials. The assessment has to cover the proof of brittle fracture safety for package components made of potentially brittle materials. This paper gives a survey of the regulatory and technical requirements for such an assessment according to BAM's new 'Guidelines for the application of ductile cast iron for transport and storage casks for radioactive materials'. Based on these guidelines, higher stresses than before will be permissible, but it is necessary to put more effort into the safety assessment procedure. The fundamentals of such a proof using the methods of fracture mechanics are presented. The recommended procedure takes into account the guidelines of the IAEA's advisory material which are based on the prevention of crack initiation. Examples of BAM's research and safety assessment practices are given. Recommendations for further developments towards package designs with higher acceptable stress levels will conclude the paper.