USING SCALE MODEL IMPACT LIMITER IN THE TYPE ASSESSMENT OF TRANSPORT CASKS FOR RADIOACTIVE MATERIAL

In Germany, the Federal Institute for Materials Research and Testing (BAM) is the competent authority for the mechanical and thermal design safety assessment of transport casks for radioactive material according to IAEA regulations. The combination of experimental and numerical safety proof forms the basis for a state of the art evaluation concept. Reduced-scale models are often used in experimental investigation for design assessment of transport packages corresponding to IAEA regulations. This approach is limited by the fact that a reduced-scale model cask can show different behaviour from a full-scale cask. The paper focuses on the peculiarities of wood filled impact limiter of reduced-scale models. General comments on drop testing with reduced-scale models are given, and the relevant paragraphs of the IAEA regulations and Advisory Material are analysed. Possible factors likely to influence the energy absorbing capacity of wood-filled impact limiting devices are identified on the basis of similarity mechanics. Among possible significant influence factors on the applicability of small scale models are strain rate and size effects, failure mechanisms, underground compliance, gravitational and friction effects. While it was possible to derive quantitative estimations for the influence of strain rate, size effects and target compliance, it was not possible to evaluate the influence of compression mechanisms and gravitation. In general, if reduced-scale models are used in proof of safety, uncertainties increase in comparison with full-scale models. Additional safety factors to exclusively cover the uncertainties of reduced-scale model testing have to be demanded. The possible application of reduced-scale models in regard to crucial aspects for proof of safety have to be analysed critically.