Architecture and management of a geological repository - Andra

4 – Waste disposal Packages4.2.3.2 Performances• Thickness of the envelope and lifetimeThe over-pack described in the previous section, has a degree of water-tightness in a disposalsituation, designed to last at least a millenium.This period covers the thermal phase, during which the core temperature of the glass exceeds 50°C.Indeed, the thermal phase 40 is evaluated to last about 150 years for C0 type packages, about 500 yearsfor C1/C2 type packages and about 1 000 years for C3/C4 type packages (see Figure 4.2.4). Theseevaluations result from three-dimensional digital modelling of heat conduction in the repository (thismodelling and its input data are described in section 5.2). They are based on (i) the age of 60 to70 years on entering the repository, for C1.C2 and C3.C4 packages respectively, (ii) a configuration ofdisposal cells and overall architecture dimensioned 41 for a maximum temperature of 100°C at theinterface between the disposal packages and the cell [10].Temperature Température the à la surface surface of disposal du colis package de stockage between entre 0 and 0 et 1600 years ansTempérature (C°)10090807060504030200 200 400 600 800 1000 1200 1400 1600Nombre d'années Number of aprés years la after mise disposal en stockageColis C3Colis C4Colis C1/C2Colis COFigure 4.2.4Evolution over time of the temperature of vitrified waste containersTo ensure water-tightness over at least a millenium, dimensioning of the effective thickness of theover-pack is based on the sum of the following two terms:- a thickness of 28 millimetres for the shell and 50 millimetres for the base and the lid, to guaranteethe object's resistance against the mechanical stresses likely to be exerted over this scale of time;- an extra thickness of 27 millimetres, defined by a penalising method, corresponding to loss ofsubstance due to generalised corrosion.• Mechanical dimensionsThe dimensions of the over-pack are such that it can resist stresses linked to vertical handling insurface installations and during transfer and horizontal handling when being inserted into the disposalcell. This point will be covered in section 4.2.3.3.In the disposal cell, as long as it has an intact sleeve, the packages are not subjected to any mechanicalstress. However, eventually the sleeve will corrode and gradually lose its mechanical strength.Deferred rock deformations will close the clearance between the rock and the sleeve and then exertslowly increasing pressure on the sleeve (estimated at a maximum of about 5 MPa at 300 years [13]).A transient thermomechanical stress generated by the release of heat from the packages is added to thepressure, wich is due to creep and to the resaturation of the argillites. After several centuries, thetemperature tends to even out in and around the cell. The thermomechanical stress has then fallen(from a maximum of 4 MPa to a residual value estimated at about 1.6 MPa [13]).4041The duration of the thermal phase increases with the maximum temperature in the repository. It also depends on the age of the waste oninstallation in the repository. The thermal phase is also sensitive to the modularity of the storage zone: it falls with the increased volumeof each module and the distances between modules.The concepts studied are based on heat dissipation by conduction in the rockDOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM136/495