Tome Architecture and management of a geological repository - Andra

5 – B waste repository zone• The radiological protection dual-gate systemThe radiological protection system dual-gate system at the cell head comprises two doors that encloseenough space to accommodate the disposal trolley (Figure 5.4.2).The transfer cask docking port comprises two motorised sliding steel panels 300 mm thick.The door opening onto the handling chamber comprises two full cell-height sliding panels (steel plateabout 300 mm thick); these panels let air through to ventilate the disposal chamber.The dual-gate system has a moving floor that carries the disposal trolley. By rotating through 180° andthrough its sideways sliding capability, it can position the disposal trolley opposite the cask to extractthe packages or opposite one of the rows of packages for the transfer operation in the disposalchamber.• The disposal trolleyThe disposal trolley used to extract the waste packages and place it in the cell is a fork-lift type trolley.A preliminary feasibility study has resulted in an assessment of its dimensions, which areapproximately 2 metres wide, by 4 metres long by 6 metres high. Its mass is about 25-30 tonnes. It canbe powered by on-board batteries.The main structure of the disposal trolley comprises two metal beams fitted with wheels. The twolifting forks slide vertically along a beam that interlinks these two beams. The mast is positioned sothat the forks are at the vertical to the beams. Thus, when handling a waste package, its centre ofgravity is inside the base formed by the wheels.This truck combines translation inside the cell with lifting for package handling. The disposal trolleymoves along rails placed in the grooves built over the whole length of the cell slab floor. In the interestof compactness, this principle has been favoured over a system with tyres.The package is kept at low level throughout the way inside the disposal chamber, to avoid any risk ofdropping and to offer stability to the moving unit.When it approaches the wall of emplaced packages, the disposal trolley gradually slows to a halt tostart package emplacement. The package is lifted to its final deposition height. The disposal trolleymoves slowly forward and positions the package above the placement line formed by the top of theupper package of the row. The package is then lowered onto it very slowly.The positioning precision of the packages when being deposited or eventually removed, raises a majortechnological issue. There are several technologies available to provide a solution. For instance, it ispossible to measure the distance travelled by the disposal trolley using a "laser distance meter", whichis commonly used in industry for ranges of up to 500 metres with a precision level to a fewmillimetres. Use of this type of process is compatible with package-to-cell wall and package-topackagefunctional clearances of about 10 cm.With regards to risk of package drops, the disposal trolley is equipped with safety devices current innuclear equipment design. For example a load lowering velocity reducing device is envisaged in theevent of a malfunction or break of an element of the lifting kinetic process.Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY147/228