Architecture and management of a geological repository - Andra

4 – Waste disposal PackagesTempérature (C°)1009080706050403020Temperature Température the à la surface surface of the du disposal colis de package stockage between entre 00 et and 2000 2000 ans years0 200 400 600 800 1000 1200 1400 1600 1800 2000Nombre d'années Number of aprés yearsla after mise disposal en stockageCU2CU1 court shortCU1 longFigure 4.3.8Spent fuel package temperature evolutions over timeSteel thickness to withstand corrosion has been determined based on the same models as for the Cwaste overpack, by adopting a penalising approach (see section 4.2.3.2). By the end of 10,000 years,the thickness affected by general corrosion is estimated at 90 mm.In the case of large diameter repository containers, the shell thickness of 110 mm contains thisthickness of general corrosion. Residual thickness of 20 mm combined with insert presence guaranteesleaktightness of the shell subjected to mechanical stress for this duration (see below).In the case of small diameter repository containers, the rated steel thickness of 120 mm results, in amanner similar to C waste containers, from the sum of the following two terms:- a thickness of 30 mm ensures resistance to mechanical stress effective at this time scale.- an extra thickness of 90 mm corresponding to assessed loss of substance due to general corrosion.• Mechanical design basisIn the long term, it is considered that spent fuel containers will be gradually loaded after loss of theone sleeve integrity and argillite convergence. The design basis adopted a pressure that is 50% higherthan are considered for C waste over-packs. This margin allows to guard against effects associatedwith the comparatively longer duration of leaktightness required for spent fuel containers. Such effectsmay be potentially higher thermo-mechanical stress, due to slower radioactive decay (actinides) andtaking into account geostatic stress anisotropy.CU1 and CU2 containers are therefore mechanically designed to take into account pressure of 18 MPauniformly applied to their walls [13].In the case of large diameter containers, the shell is supported by the solid insert. Calculations carriedout for both variants (emplacements with square or circular section depending on whether theassemblies are bare or in cladding) show that pressures exerted by the deformed shell result in stresson the insert being much lower than the cast iron yield strength limit.In the case of small diameter containers, the thickness assigned to mechanical resistance is sufficientfor the shell material to remain within elastic regime.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM151/495