Architecture and management of a geological repository - Andra

10.3.6.1 Selection of representative instrumented structuresIn view of the homogeneity of the host rock and the repetitive character of the repository structures, itis envisaged to select structures considered as representative of different categories (disposal cells forB and C waste, and possibly for spent fuels; shafts and drifts; seals; backfill). The structures selectedin this way will be monitored in a specific manner all through the repository process.At this stage of the studies, the quantity and the distribution of monitored structures can only be givenas a guide. They will be adapted in relation to the results obtained for the first instrumented structures,and management choices will be made at a later date. The knowledge gained will be put to use as therepository progresses and will enable us to specify the precise number of structures to be observed,and to optimise the distribution, and possibly to reduce the amount, of measuring equipment.The disposal cells selected for thorough scrutiny are to be known as "control cells". Other cells, whichwill be greater in number and known as "standard cells", will be measured using lighterinstrumentation equipment, to confirm the behaviour observed in the "control cells" and to transposethe results to the whole of the repository zone concerned.In the B waste repository zone, containing approximately forty cells, several different types of cell canbe identified depending on the packages they contain: bitumised waste packages, low-level exothermicpackages and gas releasing packages. One cell of each type can be chosen as a control cell, andpossibly a second cell to ensure redundancy.The C waste or spent fuel repository zones however, are characterised by a very large number ofidentical cells. Certain control cells will naturally be selected from among the first modules built.Their number, which will necessarily be very low in relation to the total number of cells, can be set ona statistical basis, at less than 10% of cells in the selected module, and at less than 1% of all the cellsneeded for the disposal of all the packages. Within the "control module", the position of the cells willbe adapted in relation to the real conditions foreseen (in particular in relation to the real thermalrelease of the package to be disposed of. Generally speaking, it may be worthwhile distributing thecontrol cells firstly in the centre of the module and secondly on the periphery of the module, so as tobe able to observe any differences in the corresponding behaviours (Figure 10.3.9).DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM400/495