Architecture and management of a geological repository - Andra

4 – Waste disposal PackagesIn addition, some waste can release traces of radioactive gas, such as tritium ( 3 H), krypton-85 ( 85 Kr),chlorine-36 ( 36 Cl), carbon-14 ( 14 C), radon-222 ( 222 Rn), iodine-129 ( 129 I) or argon-39 ( 39 Ar). Referencepackages B1 and B5 are concerned mainly (see 3.2). Dissemination should be prevented as far aspossible. In the event there is no risk of the waste package producing hydrogen by radiolysis (like theB5.2 reference packages especially), the aim is to contain these gases as close to the source aspossible. Some primary containers like the CSD-C (B1 and B5.2) can be made leaktight before beingplaced in the disposal package, by welding a plug to the vent 24 .• Accident situation managementWaste package behaviour in accident situations during emplacement in the repository must also betaken into account. In this respect, the waste disposal package will contribute to limiting the dispersionof radioactive materials during a fall or fire.• Control of long-term chemical interactionsOver the longer term, checks should be made that the chemical interactions between the materialsmaking up the over-pack, the waste itself, and the argillite are controlled.In B2 reference packages, the waste in the form of salts is closely mixed with a bitumen matrix. In thiscase, the radionuclides they contain will be released concomitantly with the uptake of water by thebitumen coating, the solubilisation of the salts and their diffusion in the permeable zone. A pHbetween 7 and 12.5 is sought to encourage the durability of the bitumen coating [40] 25 .For other reference packages, B1, B4, B5, B6 and B7, part of the radionuclides present are the resultof activation of the materials making up the waste. These activation products are found physicallyinside the metal; they are released from the waste concomitantly with the corrosion of the metal. Analkaline pH slows down steel corrosion [40].Overall, an alkaline pH in the cell is favourable to the retention of certain elements (americium,curium), by reducing their solubility.• TemperatureSome B waste has low exothermicity, linked mainly to the activation products. The heat rating ofreference packages B4 and B6 is less than 5 watts per primary waste package when they are placed inthe repository (even very much less for some B3 and B2 in particular). B1 and B5 reference packagesare more exothermic. Their rating can vary between 5 and 15 watts per primary package when beingplaced in the repository. Repository compactness, as related to disposal package design and theirarrangement in the cells, must therefore be checked to ensure that the ensuing is not excessive withrespect to the ability in describing the material changes (see Chapter 5).In this context, the containment capability or B2 waste is linked to maintaining the mechanicalintegrity of the bitumen coating. The rheological characteristics of the bitumen coating, however, areonly preserved if the coating temperature remains below 30°C. Note nevertheless that this criteriononly has a slight actual influence on the disposal package design, given the very low thermal releaseby these packages.2425This can be done when leaving the industrial storage facility or on entering the repository surface facilities; it is suitable given the smallamount of gas produced by radiolysis in these packages (no organic matter).This corresponds to the validity domain of the models adopted to describe the changes in these packages and the release of radioactiveelements.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM108/495