Architecture and management of a geological repository - Andra

5 – Repository Modules- The alkaline disturbance transforms smectites (swelling) into illites (non-swelling). It is associatedwith the presence of concrete (retaining plug and access drift lining). It develops axially, from thebearing face of the clay plug. The studies assess its extension as being 0.60 m after 100 000 yearsand under 2 m after a million years95. The disturbance can affect part of the plug but it does notreach the clay buffer of the inside part of the cell [71], [58].• Specific thermal dimensioning characteristics of spent fuel cells and modulesThe short-term thermal dimensioning criterion and calculation procedure remain identical to thoseused for type C waste (see section 5.2.3.3). Like type C cells, the thermal dimensioning of spent fuelcells depends on (i) the age (or the heat rating) of the packages on the date of placing in the repository,(ii) the distance between adjacent cells (inter-axial distance or Px pitch), (iii) the distance between thedisposal cell ends (Dy pitch), (iv) the number of packages per cell (N).However, spent fuels differ from type C waste by their initial high thermal rating, which reduces from7 000 watts to 1 000 watts in 100 years, and by their slow temperature decrease (see figure 3.2-21chapter 3). Furthermore, the concept using buffers introduces the following additional thermal data:- an 800 mm thick buffer whose thermal conductivity is lower than that of the geological medium;- two additional functional clearances around the buffer;- an increase in the minimum pitch between cells which, for geotechnical reasons, is approximately13 meters for type CU2 cells and 16.5 meters for type CU1 cells.As a result, the horizontal footprint and excavated volume of spent fuel modules are larger than thoseof type C waste modules.Results of the thermal dimensioning for the various spent fuel packagesThe repository module architectures described here have been defined for a pre-disposal storage timecorresponding to an earliest package disposal age for the concepts proposed, namely 60 years for typeCU1 packages and 90 years for type CU2 packages. For these pre-disposal storage times, thehorizontal footprints occupied by the type of package disposed in a module are summarised in Table5.3.2. The corresponding cells are shown in Figure 5.3.14.Table 5.3.2Footprint areas required for the disposal of spent fuelsDisposal package modulesLong CU 1 96 Short CU 1 97 CU2Age (years) : pre-disposal storage time 60 60 90Horizontal footprint (m 2 /packagedisposed)385 301 346No. Number of packages per cell 3 4 3Px (m) inter-axial distance between cells 22.5 22.5 24Dy (m) : DistBetween disposal cell ends 20 20 20Lua (m) : Inside length of the cell. 32 32 34.5Pc (m) : Pitch between packages 98 . 7.5 4.2 10.395969798This extension varies by a few decimetres depending on the heat rating released by the packages.Long CU1 = type AFA-2L2 package from 1300/1450 Mwe reactors; length = 5 390 mmShort CU1 = type AFA-2G2 package from 900 Mwe reactors; length = 4,640 mmThe actual pitch between packages will be adjusted according to the effective length of the buffers (constraints associated with handlingequipment, notably the transfer cask)DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM244/495