Euradwaste '08 - EU Bookshop - Europa

Figure 3.3.1 Emplacement of SF-Canister - Start niche and lock to the emplacement tunnel
(schematic)
Bentonite granulate
Emplacement trolley Bentonite granulate
SF Canister and pedestal of bentonite blocks
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Backfilling device with twin auger
Figure 3.3.2: Emplacement trolley with spent fuel canister at emplacement position (left); Wagon
emplacing bentonite granulate in disposal tunnel after a waste canister has been emplaced (right)
Results within ESDRED
The objectives of Nagra’s bentonite emplacement testing within the EC-supported project ESDRED
were as follows:
• Testing and demonstrating of suitable granular buffer installation techniques on a full scale
in surface facilities;
• Verification if the requirements can be fulfilled.
The general objectives and the experiences from previous experiments lead to an ambitious project
specific target value for the emplacement dry density of about 1500 kg/m 3 . In previous experiments
Nagra executed various tests with different bentonite types for buffer material. Because of its favorable
properties with respect to technical emplacement, bentonite granulate is used in Nagra’s reference
concept. Although small-scale laboratory experiments were performed several years ago, a
large scale test was felt to be advantageous to improve confidence that the required dry density of
emplaced bentonite granulate can actually be reached.
For this project Wyoming bentonite from Amcol Speciality Minerals was used. The sodiumbentonite
MX-80 was delivered in a conditioned, slightly granulated state to improve the pourability
and the granulation. The production of the granulated material was done in the Rettenmaier facilities
in Holzmühle, Germany. During the granulation of the bentonite, an increase of the bulk
grain dry density from 1.17 g/cm 3 to 2.10 g/cm 3 with simultaneous halving of porosity was
achieved.
The built twin auger system (Figure 3.3.3) to emplace the granulated buffer material has a total
length of about 9 m and a weight of 1350 kg. The length of the two auger casings is 7.0 m, the diameter
of the tubes are 0.2 m. The feed rate can be controlled by the auger turning speed. The rotat-