Architecture and management of a geological repository - Andra

5 – Repository ModulesA minimum annular space is required between the sleeve and the ground. The maximum value, ofabout one centimetre at the radius, corresponds to a conservative recommendation from civilengineering and mining companies and includes a margin to prevent jamming at excavation. Thisannular space will have to be adjusted to the conditions observed (on-site tests will be necessary).Whatever its initial value, this annular space will eventually close up owing to subsequent deformation(or creep) of the ground.Functional clearance between package and sleeve allows handling to take place. A clearance of a fewcentimetres (3 cm at the diameter) is currently adopted by the studies. This is compatible withhandling of the packages by pushing on sliding runners.The sleeve could be inserted into the cell in sections 76 , about 2.5 to 3.0 metres in length. The length ofthese sections must be as great as possible in order to minimise the number of connections. A 3 mlength is today considered to be the maximum allowable given the dimensions of the access drift.The joins between sections must not generate any excess thickness either on the exterior of the sleeves(so that the sleeve can be more easily pushed in) nor on the interior (so that the packages can be moreeasily inserted into the sleeve). Screwed, clamped and welded joins are the techniques currentlyavailable and that comply with this requirement.Spacers are placed between the packages when the heat rating so demands. A spacer consists of ametal envelope fitted with handling devices identical to those of the packages, and an internal matrix.The nature of this internal matrix has not yet been defined and will have to offer a compromisebetween good thermal conductivity, chemical compatibility and mechanical strength.• Description of the cell head equipment (before sealing)The diameter and thickness of the temporary sleeve are identical to those of the permanent sleeve. Thejoin between the permanent and temporary sleeves could be an unwelded force-fit to facilitatedismantling.The function of the metal plug is to act as a shield against the β, γ and neutron radiation produced bythe packages. It is installed in the permanent sleeve after the last package has been emplaced in therepository (see section 5.2.6).At the head of the cell, a shielded trap door consisting of a metal frame sealed into the access driftliner and a vertical sliding gate, provides radiological protection when closed as well as docking of thehandling devices for package emplacement. The shielded trap door is designed to be partly recoveredand reused on other cells. It is then replaced by a leaktight cover isolating the cell before it is closed, inorder to limit gaseous exchanges and create conditions favourable to controlling corrosion within thecell.5.2.3.2 Description of the access driftThe access drift is first of all determined by the package handling needs during their emplacement inthe cell.On this basis, we used pessimistic design scenarios based on the available knowledge of the site. Oncemore detailed knowledge is acquired from actual sites, more favourable scenarios could be adopted.The exercise carried out shows that these drifts are technically feasible, even with the pessimisticscenarios considered. It results in a useful access drift width of about 6.40 m at mid-height, 4.50 m atslab level and a useful height of 4.50 m. The roof support laid at excavation of the drift comprises rockbolts 4 m long 77 and a 20 cm thickness of shotcrete. The lining, laid 6 months to one year afterexcavation of the drift, consists of concrete (B60) about one metre thick.7677The section in the dead-end (the first one inserted) could be equipped with a drive shoe. This shoe would be used for excavation and leftin-situ. See section 5.2.6.The bolting diagram could be modified at the cell locaitons. In any case, the size of the anchor bolts would be less than the length of theconcrete plug in the sealing zone.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM203/495