Asse II: Fraunhofer and Bilfinger develop robots for nuclear waste recovery

The Fraunhofer Institute for Optronics, System Technology and Image Exploitation (IOSB) and the industrial service provider Bilfinger are jointly developing, among other things, recovery robots to retrieve around 126,000 barrels containing approximately 47,000 m³ of radioactive material from the several hundred-meter-deep shaft facility Asse II in the former salt mine in the Wolfenbüttel district. The return of the nuclear waste from the experimental final repository was decided in February 2013 because the safety of the facility is not guaranteed.

From 1967 to 1978, approximately 126,000 barrels of low- and intermediate-level radioactive material were stored in Asse II; high-level radioactive material was not deposited there. The barrels have since been distributed across 13 chambers in the former mine at a depth of up to 750 m. The federal government had acquired the mine in 1965 to research the final disposal of radioactive waste. However, it turned out that Asse II is not suitable for the final disposal of such material. This is because the mine is unstable and has cracks through which saline water enters. The water is currently being collected to prevent it from coming into contact with the partly corroded barrels and causing water contamination.

Due to the potential impact on people and the environment, the Bundestag decided in 2013 to retrieve the nuclear waste from Asse II as quickly as possible. The Federal Company for Final Disposal (BGE) is responsible for planning and implementation and has drawn up a plan on how this can be achieved. In a first step, the nuclear waste is to be recovered, then transferred to a lock and work area, and brought to the surface via a retrieval mine through shaft Asse 5. There, the radioactive material is to be characterized, conditioned, and finally transferred to an interim storage facility.

Robots, Special Machines, and a Digital Twin

Fraunhofer IOSB and Bilfinger are focusing on the very beginning of the retrieval chain: recovery. To this end, the two partners are developing robots, special machines, and assistance functions for the control center, which will be used to recover the partly unordered barrels. Bilfinger is currently developing a special recovery system, which essentially consists of a highly automated multifunctional experimental excavator designed as a test system. With it, the developers intend to determine the necessary handling steps for dealing with the barrels. The robot excavator has various different tools, such as special grippers, milling cutters, and buckets. The excavator must be designed to withstand continuous operation under the prevailing extreme conditions.

For automatic control, Bilfinger relies on the experience of the Fraunhofer IOSB, gained in the competence center “Robots for Decontamination in Hostile Environments” (ROBDEKON), where remote-controlled and autonomous machines are researched and developed. The focus is on sensor fusion, 3D environment perception, and machine automation. This will enable the machines to perform repetitive tasks independently, such as gripping barrels of radioactive material and packaging them in a transport box. For teleoperative tasks, an inverse kinematics system assists the operators. They can operate the machines intuitively, while the precise positioning of the tools is done automatically.

Bilfinger is transferring the entire work area of the recovery facility into a digital twin. This allows recovery steps to be planned and tested in a virtual environment before the actual recovery work begins. Furthermore, the digital twin supports a control center located at a safe distance in carrying out the recovery tasks. This way, the operating personnel cannot be contaminated, and, in addition to optical camera and other assistance systems, the digital twin provides a way to orient themselves spatially better for controlling the processes.

It is unclear how long the first recovery step of the radioactive material from Asse II will take. The BGE cannot make any predictions here – nor about the duration of the entire process up to interim storage. The costs for the preparation of the retrieval alone are estimated by the BGE at around 4.7 billion euros with an uncertainty of 30 percent. An estimate of the total costs for the complete retrieval process and the subsequent decommissioning of the Asse II shaft facility is not currently possible.

(olb)