Architecture and management of a geological repository - Andra

2 – General DescriptionThe architecture presented is characterised by the following arrangements:- the disposal cells described below are “blind” tunnels,- the groups of cells have a “dead-end” topology. A series of cells is therefore accessed via a smallnumber of close, parallel drifts as shown in Figure 2.4.3,- overall, the repository is itself in a dead-end with all shafts grouped together on a single side of therepository.The multiple seals and the possibility of a dead-end architecture complement the favourablehydrogeological characteristics of the site (low permeability of the studied formation and slighthydraulic head gradients in this and the overlying formations) in limiting the flow rates and velocity ofthe water within the repository in a particularly robust manner.Figure 2.4.3Principle of a series of dead-end cells• A favourable physical and chemical environment for wasteThe design of the disposal cells, particularly the choice of constituent materials, aims to offer afavourable physical and chemical environment to the waste packages. This intends to control theiralteration over time in order to limit the release of radioactive elements in the presence of water [9].In this respect, the concrete planned for the B waste disposal cells is a material which is favourable tothe physical and chemical protection of waste and to the retention of certain radionuclides.In the case of vitrified C waste, the use of concrete is not envisaged in the vicinity of the packages asthe alkaline conditions which it would create could accelerate glass alteration. Only metallic materialshave been considered.• Repository module separationThe repository zones are compartmentalised to reduce the quantity of waste and radionuclides thatcould be affected in a failure or intrusion situation. In this respect, each repository module consistingof a cell or a group of cells can be rendered independent of the others by a sufficient horizontaldistance between modules and by seals closing the access or connecting drifts.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM57/495