Finland’s radioactive waste management company, Posiva Oy says acceptance tests have been completed in Parkano on the installation and transfer devices of the Buffer Installation System (BIS) for the Onkalo underground used fuel repository near Olkiluoto. The world’s first ever BIS for the final disposal of used nuclear fuel has been under development by Posiva for several years. It is an assembly of several devices for the transfer and installation of the bentonite backfill between the final disposal canister and the rock.
Two special vehicles transported the 14-metre-long devices from Parkano to the Pori testing station for the implementation of system automation and its integration to the control system of the final disposal facility. The acceptance tests of the installation and transfer equipment demonstrated the functionality of the system under manual control. The automation and data transfer systems needed for remote control operation will be built at the Pori testing station. The station provides a simulation environment for testing BIS.
“The system comprises an installation device, a transfer device, and a transport container,” explains Eero Väisänen, Project Manager for Equipment Integration at Posiva. “The transport container is used to transport bentonite blocks and granular bentonite to Onkalo from an above-ground storage. The blocks and the granular material are then carried by the transfer device from the container to the final disposal tunnel where the installation device installs the backfill between the canister and the rock.”
The installation and transfer devices of BIS run on automated guided vehicle (AGV) platforms. The devices navigate independently in the final disposal repository and feature an abundance of technology facilitating remote control and automation, such as machine vision, laser sensors, and cameras. “The devices have been designed as autonomous equipment due to the radiation hazard and reasons of occupational health and safety, Väisänen noted. “The implementation of automation and remote control systems naturally requires a high degree of expertise and testing.”
Solid bentonite blocks are installed underneath and on top of the used fuel canister. The nearest blocks surrounding the canister are like pineapple rings with a hole the size of the canister in the centre. These blocks are installed in the deposition hole to about half the height of the hole before the copper canister that contains the used nuclear fuel is transferred to the final disposal tunnel. The final disposal canister is then deposited in the hole and the installation is completed with bentonite blocks and granulated bentonite. The canister is surrounded by more than 20,000 kilograms of bentonite clay.
Bentonite isolates the final disposal canister from the surrounding rock. It swells when wet, prevents water movement around the canister, and acts as a buffer should any rock movement occur over the long time horizon. The bentonite backfill surrounding the canister is part of the multi-barrier principle applied to the final disposal of used nuclear fuel.
Once the implementation of the automation has been successfully completed at the Pori testing station, the BIS will be transported to Onkalo. The transfer device was designed by Comatec and the installation device by Etteplan. The installation and transfer devices were manufactured by Parkano-based company Supersteel. Comatec also designed the transport container which was manufactured by IS Works.
