CASTOR® HAW28M - a high heat load cask for transport and storage of vitrified high level waste containers

Within the German return programme for vitrified high level waste (HLW) from reprocessing at COGEMA and BNFL up to now 39 casks loaded with 28 containers each were transported back to Germany and are stored in the Interim Storage Facility Gorleben (TBL-G) for up to 40 years. For transport and storage in all but one case the GNB casks CASTOR® HAW 20/28 CG have been used. This cask type is designed to accommodate 20 or 28 HLW containers with a total thermal power of 45 kW maximum. In the near future, among the high level waste, which has to be returned to Germany, there will be an increasing number of containers of which the heat capacity and radioactive inventory will exceed the technical limits of the CASTOR® HAW 20/28 CG. Therefore GNB has started the development of a new cask generation, named CASTOR® HAW28M, meeting these future requirements. The CASTOR® HAW28M is especially developed for the transport of vitrified residues from France [1] and Great Britain [2] to Germany. It complies with the international regulations for type B packages according to IAEA (International Atomic Energy Agency) [3]. It is thus guaranteed that even in case of any accident the cask body and the lid system remain functional and the safe confinement of the radioactive contents remains intact during transport. The CASTOR® HAW28M fulfills not only the requirements for transport but also the acceptance criteria of interim storage: radiation shielding, heat dissipation, safe confinement under both normal and hypothetical accident conditions. Storage buildings such as the TBL-G simply support the safety functions of the cask. The challenge for the development results from higher requirements of the technical specification, particularly related to fuel which is reprocessed. As a consequence of the reprocessing of fuel with increased enrichment and burn up, higher heat capacity and sophisticated shielding measures have to be considered. For the CASTOR® HAW28M new materials and new design methodologies have been developed and applied. The following sections give an overview on the design characteristics, the cask materials developed and the safety analyses performed.