Installation equipment for clay components
Underground final disposal involves several different pieces of transfer and installation equipment for clay components: AGVs (automated guided vehicles), buffer installation system (BIS) and granular backfill installation system (GBIS).
The AGVs, which are autonomously navigating and moving vehicles, serve as vehicle technology for both the buffer and deposition tunnel granular backfill installation systems.
Buffer block installation system
The task of the buffer installation equipment is to install the buffer blocks into the deposition hole. The buffer installation is done in two parts. In the first phase, solid blocks are installed at the bottom of the hole, followed by blocks with a hole in the centre to accommodate the canister. After the installation of the canister, the topmost buffer blocks are installed on top of the canister. Both of these phases also involve filling the empty space with fine-grained bentonite to seal the buffer. The installation of the buffer around the disposal canister requires therefore high precision from start to finish.
Tunnel backfill installation system
In 2019, Posiva decided that the deposition tunnels will be filled with a granule mixture, consisting of bentonite pellets crushed to different sizes. Previously, the idea was to fill the tunnels with blocks and pellets made of bentonite clay. However, this was considered to be challenging from the point of view of feasibility, which is why Posiva started to explore an alternative that would be at least as safe but financially more affordable and more industrial in terms of material manufacture and installation.
The idea of the final disposal backfill solution has been adapted from the canister-surrounding buffer solution of the Swiss National Cooperative for the Disposal of Radioactive Waste, NAGRA. The granular backfill solution ensures the functioning of the buffer surrounding the canister so that the buffer cannot rise from around the canister into the deposition tunnel.
The main task of the tunnel backfill installation machine is to transfer the granular material into the deposition tunnel filling it from the floor to the ceiling. When backfilling the tunnel, the machine is slowly reversed until the entire tunnel is filled.