COMPARISON BETWEEN DIFFERENT PRINCIPLES FOR PACKAGING DESIGNS

Over the past years, the continuous increase of burn-up of the used fuel has resulted in higher constraints for the design of transport or dual purpose casks. In the same time, the competition between cask vendors has put a high pressure on the prices. In this context, the cask designer has to make tricky choices to meet the stringent requirements of his customer and of the competent authority, while maintaining low prices. Most heavy packages consist of three main components: - a vessel, - an internal arrangement, - a set of shock absorbers. The shock absorbers are mostly used to guaranty a low level of g load in accident conditions. They also often provide fire insulation. The internal arrangement is key to the criticality safety (use of neutron poison, mechanical strength to guaranty the geometry), and to the heat transfer. The vessel has to provide the containment, the shielding and the heat transfer. The design of each component relies on two major choices: - the materials, - the type of assembly. The materials available have intrinsic characteristics such has mechanical strength, thermal conductivity and shielding capacity. Some materials have very good performances in one domain and very bad performances in other domains. Other materials seem to be good compromises between the different constraints. High performances can be obtained either by assembling several materials each of them having very good behaviour in one domain, or by assembling fewer materials being good compromises in several domains. Thus, the cask designer has first to evaluate the performance of each material and its cost. Then, to decide which materials to choose, the cask designer needs to consider not only the performance of each material separately but also how they perform when assembled together. The paper will focus on the vessel design. It will describe which materials, and which types of assembly are commonly proposed by the casks vendors and how they compare as far as safety and costs are concerned.