Architecture and management of a geological repository - Andra

2 – General Description• Waste disposal package transfer under radiological protectionDue to their irradiating character, the waste disposal packages are transferred from the surfaceinstallations to the disposal cells by means of devices providing radiological protection for personnel(shielded transfer transfer casks). Docking systems installed at the head of the cell guarantee continuedradiological protection for personnel during waste package emplacement oeperations in the disposalcell. Package handling equipment is designed in such a way that, in the event of a breakdown,assistance can be provided while still assuring this radiological protection.2.4.1.4 Quest for compactness for the underground installationsThe design and dimensioning of the underground installations are conducted with the aim ofcontrolling the total excavated volume and the footprint of the surface stockpile. The compactness ofthe repository is the result of a compromise between thermal and geotechnical requirements (whichgive priority to small, spaced out structures), the technological requirements of disposal in cells (whichlimit the length of the cells) and the quest for repository module separation.Compactness is motivated by:- a reduction of the excavated volume, limiting implementation costs and the volume of crushedrock to be stockpiled on the surface,- optimum use of the underground footprint in the Callovo-Oxfordian,- simplification of the drift network, facilitating the operation.- As a result, the principle of irradiating waste repository chambers with simple geometry has beenselected for B waste, while horizontal cells, in tunnels, are preferred for C waste and spent fuel.2.4.2 Waste disposal packages and cell design2.4.2.1 Waste disposal packages and cells for B wasteThe B waste category covers a highly diverse range of primary packages in terms of conditioning,geometry and radiological and chemical content.The concern with simplifying operating methods has led to the design of standardised disposalpackages which group together one to four primary packages in a parallelepipedal concrete containerweighing approximately 6 to 25 tonnes and measuring from 1.2 to 3 metres – see section 4.1 forfurther details. Radiological protection is not incorporated into the container as it would require anextra thickness of concrete and adversely affect the compactness objective. The contribution ofdisposal package concrete to the limitation of radionuclide release in the long term has been studiedfor exploratory purposes [41].The disposal cells are subhorizontal tunnels limited in length to approximately 270 metres – a detaileddescription is provided in section 5.1. As B waste packages are only slightly exothermic, if at all, theexcavated diameter of the cells is essentially the result of the geotechnical analysis and thecompactness target. It is limited to 12 metres at most.The concrete drift liner gives the engineered structure mechanical stability. Selected first and foremostfor its mechanical qualities and its durability favourable to reversibility, the liner concrete alsoprovides chemical protection for the packages and contributes to radionuclide retention. Its innersection is a rectangular shape and delimits a repository chamber in which the packages are stackedover several levels.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM59/495