Architecture and management of a geological repository - Andra

Figure 10.4.3Cell filled with B packages after sealing• Cell restoration to workable condition processAfter closing the cell, the package retrieval operation proper is preceded by a phase for characterizingthe condition of the cell and of the packages contained therein. The characterization results are thenutilized to determine the prior work to be undertaken to restore the cell to its workable condition.Checking the cell atmosphereChecking the atmosphere in the cell may be performed by means of a horizontal drilling tube insertedinto the drift entrance and run through the seal down to the internal side of the cell head sectionconcrete fill (Figure 10.4.4). This drilling should be carried out in a neutral atmosphere maintained byan airlock.Once drilling is complete, the cell may be subjected to atmospheric pressure and its atmosphere maybe checked. This check consists in drawing and analysing a gaseous sample from the drilling operationperformed in the seal. Its purpose is to verify the hydrogen and radioactive gas content of the sample.Should the hydrogen content of the cell atmosphere exceed the lower explosive limit (4% ofhydrogen), the cell atmosphere shall be renewed. The atmospheric check shall be performed as closeto the cell as practicable by means of a portable device including a vacuum pump, a safety filter, apressure gauge and a hydrogen detector.Figure 10.4.4Checking the atmosphere of a B cell by drillingCell ventilationWhen drilling is complete, it is recommended–for the purpose of the ensuing operations–to dischargethe hydrogen from the cell (especially for cells containing B2/B3/B4/B6.4 type packages) as well asthe gaseous radionuclides given off by the packages, if any. Ventilation also reduces the temperatureon the access drift wall in the case of cells containing low exothermic packages (B1 and especially B5type packages).DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM422/495