Architecture and management of a geological repository - Andra

3 – High Level Long-Lived WasteThe EL4 fuels represent about 50 tonnes of heavy metal. The fuel element is in the form of a 19-rodcluster fitting tightly in an ATR structure (alloy of zirconium with copper and molybdenum). The rodsare made up metallic cladding in a zirconium-copper alloy and contain uranium oxide pellets veryslightly enriched with uranium-235 (1.28% or 1.41% depending on the rods). The initial weight of theuranium oxide is 10.6 kilograms per cluster. The EL4 fuel clusters are currently conditioned instainless steel claddings about 100 mm in diameter and 1100 mm long. Each cladding contains twoclusters placed on top of each other. Their heat rating is also very low (maximum 10 watts percladding).The Célestin fuel elements are made up of metallic plates containing enriched uranium, mounted on ametallic structure. They are conditioned in stainless steel claddings around 340 mm in diameter and1100 mm long. Each cladding holds six fuel elements representing a total heat rating of 120 wattsmaximum.The nuclear propulsion fuels are made up of (i) oxide fuels based on sintered uranium oxide plates and(ii) metallic fuels based on highly enriched metallic uranium. These latter fuels are no longer used.In both cases, the fuel takes the form of an assembly made up of several bundles. The bundles areseparated from the assembly and conditioned in identical diameter claddings (340 mm approximately,like the claddings containing the Célestin fuel elements), but of different lengths to suit the bundledimensions. Each cladding contains four or six bundles from the same type of fuel assemblies. Theheat rate here is at most in the same order of magnitude as for the AVM vitrified waste packagesdescribed above (155 watts).3.3 Inventory modelAll the preceding data and hypotheses on the primary waste packages have been collated in an"inventory model", for systematic use in the study.This inventory model organizes the diversity of primary waste packages (presented in section 3.2) intoa tree-live structure. This structure groups those packages raising similar (waste management) issues.To cover the characteristics of the primary packages thus grouped, the inventory model defines "wastepackage types" that are representative of these groups.The tree-live nomenclature adopted to identify the waste package types will be used throughout thefollowing chapters. It has three levels. Level 1 differentiates in traditional fashion between the variouspackage categories (B waste, C waste and spent fuels identified by the letters "CU") that present theirown issues given their radiological content (type and quantity) and thermal consequences (thermalrelease levels and changes over time). Various types of packages are identified within each of thesecategories, particularly for category B waste, based on waste type (sludge, technological waste,cladding waste from fuel assemblies, etc.) and conditioning methods (compacting, bituminisation,cementation). Breaking down level 1 packages into one or even two additional levels provides greaterdetail on the variability of primary waste packages for design study, modelling and repository safetyevaluation purposes. The following criteria are taken into account to differentiate between level 2 orlevel 3 waste package types: physico-chemical characteristics of the conditioned waste (in connectionwith the waste material and conditioning matrices), heat rating and irradiation levels of the packages(in connection with the radiological inventory) and container characteristics (dimensions, materials).Note that for waste package types encompassing a wide range of primary package families, such as theB3 waste package type, a second level in the tree is created to group packages initially based on thetype of package materials (concrete, steel) and whether or not the conditioned waste is homogenous.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM97/495