Tome Architecture and management of a geological repository - Andra

7 - Spent fuel repository zone7.1.3 Throughput hypotheses for spent fuel package receptionCU2 fuels identified in scenarios S1b, S1c and S2 would be received after a currently-estimatedtemporary storage period of 70 tot 90 years (according to granite temperature at disposal depth). At anannual rate of 150 assemblies, resorption of their stored inventory will take place over about fortyyears under scenarios S1b and S1c (or thirty for scenario S2).Lastly, for CU1 fuels (scenario S1), the study considers the hypothesis of 1,650 assemblies per year.Note that an annual reception rate of 400 primary claddings can be envisaged for CU3 fuels,corresponding to a resorption of their stored inventory over about fifteen yearsThese throughput hypotheses entail emplacing two disposal packages per day in the granite formation(see below).7.2 Safety options for the design of a spent fuel repositoryThe general principles underlying spent fuel repository design in granite medium are the same as thoseformulated for the HLLL waste repository described in section 3. They entail long-term safetyfunctions, waste disposal and management of the installations with a view to reversibility. Thefollowing principles are adopted for long-term safety:- harnessing the favourable properties of the granite medium;- designing engineered components that are complementary and redundant to the granite medium;- limiting disturbances to the granite by the repository.In the framework of these general principles, designing a spent fuel repository zone is similar to thevitrified C waste zone case. However it differs in that the assemblies release heat (§ 7.1) and that theradionuclides they contain have no primary conditioning. Managing the repository behaviour calls forincorporating the temperature criteria that restrict the number of packages per cell (heat ratingmanagement) and spacing between cells (heat dissipation management).7.2.1 Harnessing the favourable properties of the granite mediumAs in the case of C waste, harnessing the favourable properties of the granite medium happens on twolevels, firstly on the scale of the cells by seeking sites in those parts of the rock where there is verylittle fracturing, and secondly at the scale of the disposal module, that are developed away from waterconductingfaults (§ 6.2.1).7.2.1.1 The reference cell: small disposal boreholesInternational studies have been conducted on different types of cells, horizontal tunnels and verticalboreholes for spent fuel disposal (Figure 7.2.1 [53]).The Swedish KBS-3 reference design is based on the disposal of spent fuel in short vertical boreholes,called as well pits (KBS3-V) [54]. However the Swedish agency SKB, and the Spanish agency,ENRESA are also studying a horizontal design. In Canada both the horizontal and vertical optionshave been studied.Dossier 2005 granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY198/228