Euradwaste '08 - EU Bookshop - Europa
Euradwaste '08 - EU Bookshop - Europa Euradwaste '08 - EU Bookshop - Europa
which was relatively homogeneous in terms of density and water content and which exhibited a relatively steep and regular slope, although generally the result was more positive for the bentonitebased materials than for the sand-based materials. Based on the above, it was concluded that the test had been a success. Measured results are summarized in Table 3.2-1. The thermal conductivity is relatively low for some cases and probably on the edge of what would be acceptable. The tests did not address the issue of chemical compatibility with the Supercontainer concept. Figure 3.2.3 Granular materials backfill test configuration and nozzle in operation (June-Oct. 2006) Table 3.2-1. Summary of measured operational and materials data in the dry-gun backfill tests Tested material Density [kg/cm3] Pure sand (SiO2) Sand/cement (90 / 10) not measured (but typically 2.1 saturated and 1.6 dry) comparable to pure sand Pure bentonite 1.391 (MX-80) 1.043 (dry) Bentonite/sand 1.442 (75 / 25) 1.092 (dry) Bentonite/cement (85 / 15) Full scale mock-up testing 1.528 1.131 (dry) Water content [%] 246 Thermal conductivity [W/m-°C] not measured not measured (but typically 2.7 saturated and 0.35 dry) Compression strength [MPa] not applicable 7.0 2.944 ± 0.133 not measured (but typically 2 to 5 MPa) 33.4 0.619 ± 0.011 0.200 32.0 0.842 ± 0.017 0.110 35.1 0.653 ± 0.016 0.670
On April 8 th 2008, the grout injection backfill technique was tested on a 30 m long, full-scale mockup of a disposal cell. This time, the heater inside the sand-filled tube was set to obtain an initial average tube surface temperature of 60°C. It took about 6 hours, at an average rate of 15 m 3 /h, to fill up the annular void. It is currently foreseen to investigate the resulting backfill through borehole sampling and cutting a slice of the mock-up (see Figure 3.2-2). It will depend on this investigation whether the test can be called a success. An important lesson already from this test is that the logistical needs behind the backfill operation increase considerably if longer sections of disposal drift are taken. The possibility to satisfy those needs in underground conditions may turn out to be the determining factor in the limitation of the section length. 3.3 Buffer of granular material in horizontal configuration of waste container resting on prefabricated buffer blocks (NAGRA) Disposal concept / design [3] [5] The engineered barrier system foresees a massive steel canister and a bentonite backfill. The bentonite consists of a hybrid system: the canisters are emplaced on a pre-fabricated pedestal of bentonite blocks and the remainder of the emplacement tunnel is backfilled with a bentonite granulate. Underground transport of the waste packages is in the reference case by rail systems using transport casks (shielding) for the disposal canisters. The emplacement is done by specially designed equipment that allows remote handling. Backfilling of the emplacement tunnels is also performed by remote handling. All of the emplacement equipment is on rail tracks and is powered by electric drive and winches since the emplacement tunnels are inclined between 4 and 6% according to the subhorizontal host rock layer. The following figures illustrate the emplacement sequence: • Transfer from surface to the repository level is carried out by common rack locomotives. In the central area at repository level the wagon carrying the transport cask (shielding) is shunted to a tunnel locomotive (Figure 3.3.1, left); • A pedestal of bentonite blocks is positioned on the emplacement trolley at the enlarged branch tunnel of each emplacement tunnel (Figure 3.3.1, right). The branch tunnel is equipped with double track and a lock; • The transport cask with a waste canister is positioned beside the emplacement trolley. After all preparations are completed operators leave the lock. All the subsequent activities will be carried out using remote operations. The canister is now pushed off the transport cask by the hydraulic device 1 (hydraulic wagon) and moved to the emplacement trolley by the transload equipment (Figure 3.3.1, right) • The emplacement trolley is driven by gravity and controlled by a winch locomotive within the lock up to the emplacement position (Figure 3.3.2, left). At emplacement position pedestal and canister are lowered subsequently and the emplacement trolley is pulled back to the lock • After a waste canister has been emplaced, the remaining tunnel is backfilled with bentonite granulate using twin augers and a wagon which is pulled back continuously by winches while backfilling (Figure 3.3.2, right). 247
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which was relatively homogeneous in terms of density and water content and which exhibited a<br />
relatively steep and regular slope, although generally the result was more positive for the bentonitebased<br />
materials than for the sand-based materials. Based on the above, it was concluded that the<br />
test had been a success. Measured results are summarized in Table 3.2-1. The thermal conductivity<br />
is relatively low for some cases and probably on the edge of what would be acceptable. The tests<br />
did not address the issue of chemical compatibility with the Supercontainer concept.<br />
Figure 3.2.3 Granular materials backfill test configuration and nozzle in<br />
operation (June-Oct. 2006)<br />
Table 3.2-1. Summary of measured operational and materials data in the dry-gun backfill tests<br />
Tested material Density<br />
[kg/cm3]<br />
Pure sand<br />
(SiO2)<br />
Sand/cement<br />
(90 / 10)<br />
not measured<br />
(but typically 2.1<br />
saturated and 1.6 dry)<br />
comparable to pure<br />
sand<br />
Pure bentonite 1.391<br />
(MX-80) 1.043 (dry)<br />
Bentonite/sand 1.442<br />
(75 / 25) 1.092 (dry)<br />
Bentonite/cement<br />
(85 / 15)<br />
Full scale mock-up testing<br />
1.528<br />
1.131<br />
(dry)<br />
Water content<br />
[%]<br />
246<br />
Thermal conductivity<br />
[W/m-°C]<br />
not measured not measured<br />
(but typically 2.7<br />
saturated and 0.35<br />
dry)<br />
Compression<br />
strength<br />
[MPa]<br />
not applicable<br />
7.0 2.944 ± 0.133 not measured<br />
(but typically<br />
2 to 5 MPa)<br />
33.4 0.619 ± 0.011 0.200<br />
32.0 0.842 ± 0.017 0.110<br />
35.1 0.653 ± 0.016 0.670
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