Architecture and management of a geological repository - Andra

5 – Repository Modules5.1.1.1 Quest for repository compactnessA simple answer as regards regrouping and standardisation of disposal packages has been brought tobear upon the variety of primary packages, regrouping them in parallelepipedic concrete disposalpackages 57 , as described in Chapter 4. At the same time, total B waste package volume involvesdesign of compact repository modules to minimise amounts of rock to be excavated for disposal of theentire inventory.This quest for compactness must nevertheless be compatible with control of rock damage,temperature, and the sub-critical state of some packages.5.1.1.2 Safety during works phaseDesign of B waste disposal cells must allow:- ensurance of mechanical stability of structures during operation,- protection of personnel against radiation,- management of gases which may be emitted by certain packages.• Ensuring mechanical stability of structuresWhen package disposal operations commence, the cell must be inaccessible due to package irradiatingproperties. Any lining maintenance operation therefore requires temporary removal of disposedpackages. In order to simplify disposal management, it has been decided to design lining to ensure cellmechanical stability throughout package emplacement and after, with a view to reversibility. Multicenturydurability is targeted.• Protecting personnel from radiationDuring package emplacement, maintenance and monitoring operations, operating personnel must beprotected against direct radiation from packages and also from radiation caused by the very smallquantities of radioactive gases some of them may emit.• Evacuating gasesMost B waste produces hydrogen by radiolysis of material it contains. As well as the above-mentionedneed to protect personnel against radioactive gases, special attention must be paid to control of risksassociated with the presence of hydrogen in the air inside cells and drifts.5.1.1.3 Long-term safetyRegarding the long-term safety measures described in section 2.1.2, cell design contributes to:- conserving favourable environmental conditions by limiting disturbances due to disposal,- temperature control,- maintenance of sub-critical state for B packages containing traces of fissile elements,- control of water circulation around and within modules and cells,- splitting up of disposal so as to limit radiological effects in certain hypothetical situations,- protection of primary and disposal packages from physico-chemical alterations which couldaccelerate their deterioration,- retention of certain radionuclides.57It is worth mentioning that these disposal packages have no role of biological shielding in the quest for compactness.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM161/495