MAINTENANCE OF PACKAGE DESIGN SAFETY REPORT EFFECTIVENESS OF SNF and HLW DUAL PURPOSE CASKS

For interim storage of spent fuel or HLW in many countries transport casks are used. The design of these “dual purpose casks” has to be assessed and approved to transport regulations (based on IAEA SSR-6), and to be assessed within the storage facility licensing procedure. Although the transport cask design differs from the storage cask design, e.g. by use of impact limiters, the majority of cask components is identical for both. Differences occur also in the acceptance criteria; these are for the transport case defined in IAEA SSR-6, and have to be developed for the storage case based on the storage conditions. Considering transport after several decades of storage requires the implementation of ageing behavior into the transport safety case. Additionally the transport package design safety case has to be maintained in an up-to-date state, considering potential regulatory changes and development of scientific and technical knowledge. The review of a transport package design safety case has to be done periodically, implemented in periodic re-assessment for extension of the package design approval certificate. The review process (as a kind of “intellectual periodic inspection”) should be part of the approved applicant’s management system. From experience we have seen that stability of regulatory requirements for Type B(U) packages was not a major problem, but consideration of ageing and developments regarding the state-of-the-art technology can cause necessary adjustments of specific technical evaluation, with the result of confirmation of package safety, or with the development of appropriate compensatory measures to reach the required level of safety. This paper will draw some examples from the past to explain the problems in periodic transport safety case reviews.