ASSESSMENT FEEDBACK ON MATERIAL COMPATIBILITY AND DETERMINATION OF MATERIAL PARAMETERS FOR TRANSPORT PACKAGES USED AS DUAL PURPOSE SNF AND HLW CASKS

In Germany dual purpose casks have to be assessed concerning material corrosion and aging, i.e. that a transport has to be considered within or after several decades of interim storage. The knowledge of reliable mechanical, physical, and chemical material properties of the cask components is necessary for safety analysis. Furthermore it is important for appropriate inspections which are necessary, e. g. during preparation for a transport after the interim storage period. In recent years BAM developed recommendations for an appropriate documentation applied in Safety Analysis Reports. We describe approaches and experience on assessment of material compatibility of cask components of SNF and HLW transport packages. The IAEA regulations [1] -SSR6, § 614 require that materials of the packaging and any components or structures shall be physically and chemically compatible with each other and with the radioactive contents. Account shall be taken of their behavior under irradiation. Also the loading and unloading operation and the specific situation of dual purpose casks during storage at an interim storage facility before a final transport have to be considered. These operational phases are the basis to derive boundary conditions for the analysis of the chemical and physical compatibility of each material used and of materials/components among each other. Different types of degradation mechanisms such as surface corrosion, galvanic corrosion, pitting, stress corrosion cracking, and crevice corrosion, hydrogen embrittlement as well as aging processes resulting from radiation and/or high temperatures have to be examined depending on the operational phase and the design of the package. Furthermore the competent authority assessment requirements by BAM regarding the documentation and verification of material properties and data will be shown. Numerical analyses have an increasing significance for the safety case methods of package designs. The accuracy of the material behavior description and their verification depends among others on the amount and quality of the available material properties data. The material data have to be verified for materials used in a traceable and plausible documentation. The behavior of materials and components under high temperature and under long term interim storage has to be assessed in an appropriate way as well.