Architecture and management of a geological repository - Andra

10.4.2 Retrieval of C waste (and spent fuel) packages10.4.2.1 Design factors favourable to package retrievalThe design of the packages and disposal cells is characterized by three major elements favourable to aretrieval operation, where required: the existence of a durable handling set, the durability of disposalcontainers and the presence of ceramic elements insulating the packages from the cell sleeve.• Durability of the cell sleeve stabilityThe first design factor favouring retrieval of thepackages is related to the dimensioning of the sleeve.The thickness of this sleeve is calculated to reducelongitudinal and radial deformations over a period ofone or several hundred years. It contributes to thepreservation, during this period, of the handlingclearance between the sleeve and the package andfacilitates retrieval if necessary (Figure 10.4.9).• Durability of disposal containersThe second design factor favourable to the retrieval ofpackages is the durability of the disposal containers(4,000 years for C waste packages and 10,0000 yearsfor spent fuel packages).• Insulation of the disposal packagesusing ceramic elementsThe third design factor favourable to the retrieval isrelated to the presence of ceramic pads fixed to C andCU2 type spent fuel disposal packages. For CU1 typespent fuels, one similar provision consists in coatingwith ceramic the tracks attached to the sleeve on whichthe packages are installed. Ceramic avoids steel-tosteelcontact with the sleeve and prevents sticking bycorrosion which is likely to occur when two same typesteels are in contact. The radiological protection plug iscoated with ceramic for the same reason.Figure 10.4.9 Functional clearancebetween a package and the sleeve ina C cell10.4.2.2 Retrieval conditions at the “After package installation” stageThis stage corresponds to a configuration in which all of the C or spent fuel packages have beeninstalled in the cell (Figure 10.4.10). A metal plug is placed inside the cell to protect the personnel inthe access drift from radiations. The cell head section is equipped with a) the shielded trap door usedto introduce the packages, and b) with a simple leaktight cover. These mechanical devices may beopened at any time for the purpose of withdrawing the packages. The ventilation system of the accessdrift is maintained in service with a reduced output. The flow can be temporarily re-established duringintervention by personnel.During this stage, the emplaced packages may be managed as under storage conditions over a 100-year to multi-century period. However, package retrieval may be preceded by an operationalinspection phase of the cell head section.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM426/495