Architecture and management of a geological repository - Andra

The purpose of this chapter is to describe the disposal management principles with the aim of ensuringreversibility. As indicated in Chapter 2, reversibility is not dependent on purely technical factors. Itaims to meet the social expectations of retaining freedom of choice. This chapter illustrates thetechnical provisions that make it possible to offer this possibility. These provisions must thus allowchanges to be made, when desired, in waste management.The chapter starts by describing the paradigm of a progressive waste disposal process, which consistsof constructing, operating and closing the repository by means of a succession of stages, the durationof which is not pre-determined. The fact is underlined that this progressivity makes it possible, over aperiod of several centuries, to manage the disposal process with a flexibility similar to that offered bya storage facility, i.e. so as to be able to retrieve waste packages from disposal if necessary or desired.This progressivity also allows the closing of the repository to be controlled in an adaptable, flexiblemanner whilst retaining the option of reversing the process. It is also stressed that this progressivityoffers the ability of changing the design of the repository and allows to baskfill from experiencegained during the initial construction.The chapter then goes on to describe the principal phenomena that characterise the various key stagesof the process. It analyses their impact on the condition of the packages and the argilite from the pointof view of reversibility and the possible options available in terms of process management. It alsounderlines the ability to take action on the disposal process.It provides a description of the resources available for monitoring phenomena throughout the disposalprocess. It stresses the extent to which advantage can be taken of monitoring experience feedbackfrom operators of major public works. It shows that at each stage, reliable, durable measuringtechniques can thus enrich knowledge and provide additional elements, particularly in decisionmakingwhen moving from one stage to the next.Finally, this chapter proposes an outline of the technological resources that could be brought into playif it was decided to reverse the previous stages of the disposal process and retrieve the waste packages.It demonstrates the technical feasibility of such an eventuality.10.1 Stepwise managment of the disposal processThis section identifies the various stages of the disposal process, from receipt of the first packagesthrough to closing of the entire repository.10.1.1 Progressive operation of the repositoryThe industrial commissioning of the installation begins with the on-site receipt of the first wastepackages and their placing in the repository in the first disposal cells constructed. At the same time asthese cells are being brought into use, the construction of new modules could progressively begin.Thanks to the design of the infrastructures, using separate shafts and drifts for construction anddisposal activities, it is possible for both types of activity to co-exist and for them to progressindependently of each other.All type B cells could be progressively constructed and operated over a period of 40 years at a rate ofone new module annually. All type C modules could be built and operated over a period ofapproximately 50 years at a rate of one new operating unit initiated every two years.If spent fuel were to be placed in the repository, the rate of progress could be one operating unitapproximately every two years for type CU2 spent fuel and one per year for type CU1. The overallconstruction and operating periods would then be approximately 35 years for type CU1 spent fuel andapproximately 30 years for type CU2.Thus, in order to resorbe all the waste packages under reasonable technical and economic conditions,the disposal period would be at least several decades and could last on the other of a century. Thisestimate, based on the inventory of French waste packages, is of the same order of magnitude in otherEuropean countries.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM366/495