Qualification of neutron absorber material families for dry storage systems

The need for qualification of neutron absorber materials has become an urgent topic in the field of dry fuel intermediate storage systems in Switzerland due to requalification of existing cask designs for increased content requirements. A special issue is the material which is used to manufacture the baskets of casks for spent fuel, mainly borated aluminium. This material has to fulfil several requirements for example to ensure subcriticality, to sustain stability under mechanical loads and to dissipate heat. These requirements also depend on the design of the casks and have to persist over the long period of intermediate storage under continuous high thermal load. This paper starts with the definition of the necessary requirements by the help of numerical analysis of accident and service conditions at storage sites with specific respect to regulatory environment. In addition the applied methods for the qualification of the long term material behaviour will be described from the perspective of the Swiss regulator. Special challenges of the current qualifications are the variations of boron content and geometrical dimensions within the same family of material. In addition there are manufacturing limitations which can also have impact on the material behaviour and properties. These aspects require an adapted supervision of the manufacturing process. Qualification requirements have to be respected during the on line material production. Examples for necessary procedures during supervision of the mass produced material are provided as well as specific long term demonstrations.