Demonstration of gap fill material delivery technology to backfill placement room voids

The placement rooms for long term used fuel storage in the deep geological repository are to be excavated using drill and blast techniques. The rooms are approximately 3.2 m wide and 2.2 m tall to fit one Buffer Box wide, stacked 2 high through the length of the room. Due to the undulating wall profile, the resulting distance between the rock and the Buffer Boxes is expected to range from 100 to 250 mm. The resulting void must be backfilled with Gap Fill Material (GFM) to achieve the required dry density of the bentonite engineered barrier. The GFM is compacted bentonite that is granulated to a specific particle size distribution to efficiently fill the void. The as-placed GFM must meet a minimum dry density requirement of 1410 kg/m³. The method currently being tested by the NWMO to place the GFM is by screw conveyor. Initial bench testing was conducted using commercially available equipment to test GFM delivery into a 1 m x 1 m x 0.15 m test box. Bench testing with an alternate, GFM-like material achieved equivalent as-placed dry densities that exceeded the 1410 kg/m³ requirement. A custom screw conveyor system has been specifically designed and fabricated to test and develop the process for filling the void in a simulated, full size room section. The system is capable of moving the screw conveyor vertically up the walls of the room and horizontally across the top of the buffer boxes. The screw conveyor is designed to withstand a 225 kg axial force to push the GFM into the void and fill all the wall surface irregularities to achieve the required dry density of 1410 kg/m³. (author)