Tome Architecture and management of a geological repository - Andra

6 – C waste repository zoneFor the concepts studied, a package cooling period is required prior to acceptance by the repository sothat the temperature criterion is not exceeded (cf. § 6.2.2.3). The interim storage period has little to dowith the thermal characteristics of the granites as envisaged in the French context [42].6.4.1 Description of a disposal cellThe reference disposal cell for repository studies in a granite medium comprises a vertical disposalborehole with an engineered barrier. The disposal borehole diameter varies from about 1.80 m(reference packages C02 and C1-C4) to 1.90 m (reference packages C0.1 and C0.3). The depth of sucha disposal borehole for two C packages (C1 to C4) is about 7 m. In the case of a boreholeaccommodating 5 C0 packages, this depth is about 10.2 m. It increases to 11.8 m for the disposal ofC0.2 packages, which are the tallest.A cell comprises two parts:- the useful part of the cell is equipped from the outside inwards, with a 60-cm thick swelling clayengineered barrier and a permanent metal sleeve containing two to five disposal packagesdepending on their heat rating;- the borehole head will accommodate the cell seal, comprising from bottom to top, a 1.5-m highswelling clay plug and 1 m of slightly permeable compacted backfill.Figure 6.4.2General dimensions of C waste cells• The swelling clay engineered barrierThe following main properties are expected of the engineered barrier:- low permeability with a target of about 10-11 m/s;- the highest possible thermal conductivity; over 1.5 W/m/°C in the long term (resaturated material)and 1.2 W/m/°C during the thermal peak (if the material is not yet saturated);- adequate mechanical strength (resaturated material) to prevent that the column of packagespunches the engineered barrier at cell end.Dossier 2005 granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY176/228