Architecture and management of a geological repository - Andra

4 – Waste disposal PackagesFor emplacement of the waste packages in the cell, the search for simplicity and reliability anticipatestwo conditions: (i) reduced flux of objects to be handled and (ii) little physical difference in the objectsintroduced into the same cell.The residual voids in the cells after emplacement of the waste packages also need to be minimised orfilled. Indeed, the ultimate resorption of these voids is likely to cause deformation to the argillite,which should be limited in order to contain the extent of a potentially fissured argillite zone in thevicinity of the cell.Large packages with simple, regular geometry and just enough clearances for handling purposescontribue to preventing the need for filling; this simplifies operations in the cell whilst controllingdeformations in the argillite.Lastly, simple emplacement processes and not having to fill the residual voids between the packagesare two particularly favourable factors in reversibility, making it easier to retrieve the disposedpackages.Overall, the B primary waste packages do not unite these conditions for compactness and repositoryreversibility. Firstly, they come in large numbers and at a high flux rate (B waste represents around200,000 primary packages, for a volume of 80,000 cubic metres, see Section 3.4 and [3]). Secondly,given their diverse origins and the history of the facilities producing them, the B primary wastepackages have very different characteristics (see Section 3.2 and [3]). By way of example, the primarypackages vary in diameter and height from 0.4 m to 1.6 m and from 0.7 m to 1.7 m respectively. Theyweigh between 0.3 and 9 tonnes. Package materials are as diverse as carbon steel, stainless steel andconcrete. Lastly, more than ten gripping systems specific to each origin facility exist, including somethat are incompatible with the objective of limiting handling clearances.Thus the first interest in waste over-packing is to simplify waste disposal and its possible retrieval andmake both more reliable: firstly, grouping smaller primary waste packages in higher-capacity disposalpackages reduces the flow of objects being transferred in shafts and drifts, then handled into the cells;secondly, over-packing standardises the dimensions and handling methods of these objects. In order tolimit long term deformations in the argillite, it minimises the residual empty spaces in the cell andtherefore avoids having to filling in situ residual clearance around the primary packages. Lastly, it cancontribute to reversibility through the choice of materials unlikely to alter greatly in repositoryconditions, which will facilitate the eventual retrieval in a period of at least one hundred years.4.1.1.2 Other issues relating to waste disposal package designA variety of questions linked to operational and long-term safety must be taken into account in theover-packing design.• Waste produced gas managementThe organic matter contained in some waste, the bitumen coating on the B2 packages (see § 3.1.2) andthe water used in mixing mortar and cement of a large number of primary packages (see § 3.2)undergo a radiolysis phenomenon. This phenomenon is triggered by radiation issued by theradionuclide content in the waste; it slowly produces gas, mainly hydrogen. This productionphenomenon exists in reference packages B2, B3, B4, B5.1, B6.4, B7.1, B8.1 and B8.2. Anaccumulation of the hydrogen produced must therefore be prevented in the disposal package. Toachieve this, the disposal package must be capable of evacuating the hydrogen produced by the wastein question.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM107/495