Reliable testing of transport and storage containers for radioactive waste

Containers for radioactive waste must be capable of withstanding extreme stresses, including vibrations and traffic accidents during transport, as well as elevated temperatures during storage. They are therefore subject to strict safety criteria. They are usually made of ferritic cast iron, which is relatively soft, malleable, and has good damping properties. Material stress tests are mandatory for practical applications, but so far they have been very time-consuming and resource-intensive.

Researchers at the Materials Testing Institute (MPA) of the University of Stuttgart, in cooperation with the Federal Institute for Materials Research and Testing (BAM), aim – within the framework of the project “Investigation of the Master Curve for Ferritic Cast Iron with Spheroidal Graphite under Dynamic Loading” (MCGUSS-2) – to transfer an already validated method for the reliable testing of safety-critical steel components to ferritic cast iron materials. The Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMUKN) is funding the project with 840.000 euros. During a visit to the MPA, Parliamentary State Secretary Rita Schwarzelühr-Sutter presented the grant notification to Anna Steiger, Chancellor at the University of Stuttgart; Professor Stefan Weihe, Director of the MPA; and Marcel Holzwarth, Project Manager of MCGUSS-2.

“Germany is actively working to identify a final disposal site for high-level radioactive waste that ensures the highest possible level of safety. We are already closer to solving the nuclear waste problem than many other countries with nuclear power plants. And we are very keen to speed up this process,” says Rita Schwarzelühr-Sutter. “However, if extending interim storage is necessary, safety must of course be the top priority. Through this joint research project, the Stuttgart Materials Testing Institute and the Federal Institute for Materials Research and Testing are helping to characterize the durability of the materials used in the containers in accordance with the highest safety standards."

“For decades, the Materials Testing Institute at the University of Stuttgart has been synonymous with the highest safety standards and practical solutions at the intersection of science, industry, and society. Through their work, the researchers at the MPA are making a substantial contribution to the protection of people and the environment,” says Anna Steiger, Chancellor at the University of Stuttgart. “Projects like MCGUSS-2 demonstrate how we develop specific solutions to societal challenges through scientific excellence and interdisciplinary collaboration. The funding from the Federal Ministry for the Environment motivates us to further advance our research toward even higher nuclear safety standards.”

“At present, there is no validated method for a clear and reliable assessment of brittle fracture in ferritic cast iron,” says Professor Stefan Weihe, Director of the MPA. Extensive stress tests involving real-world scenarios are standard practice. In the process, numerous containers – previously manufactured using energy-intensive methods – are destroyed. “We want to provide a resource-efficient and highly reliable method that requires only a few practical trials.”

Weihe and his team at the MPA aim to adapt the Master Curve method for evaluating brittle fracture in steel to ferritic cast iron. Using this method, the researchers focus primarily on fracture toughness. It provides information about a material's resistance when external forces act upon it. Materials such as glass or ice shatter instantly into a thousand pieces. Steel or cast iron, on the other hand, can withstand this – as evidenced, for example, by cracks in the material. “The main focus of our project is to reliably and unambiguously predict this fracture resistance as a function of temperature,” explains Marcel Holzwarth, who will lead the MCGUSS-2 project.

The Master Curve method not only saves resources and eliminates the need for time-consuming tests, it also allows for a more effective assessment of current high safety standards. The researchers were able to map the relationship between fracture toughness and temperature over a wide range. This is particularly important when it comes to the interim and final storage of radioactive waste, as the containers are exposed to extreme temperatures of several hundred degrees Celsius. “If we succeed in applying the Master Curve to the fracture assessment of ferritic cast irons, that would be an important step toward further developing international standards for nuclear safety research,” says Weihe.

About MCGUSS-2
The MCGUSS-2 project (Investigation of the Master Curve for ferritic ductile cast iron under dynamic loading) is being funded with 840.000 euros from the Federal Ministry for the Environment, Climate Action, Nature Conservation, and Nuclear Safety over a three-year period. As part of the project, researchers are developing a method for the fracture mechanics analysis of ferritic cast iron materials used in transport and storage containers for radioactive waste. The goal is to adapt the proven Master Curve method for fracture analysis of steel to cast iron in order to achieve a more resource-efficient and effective evaluation. The MCGUSS-2 project is led by the Materials Testing Institute (MPA) at the University of Stuttgart, with contributions from the Federal Institute for Materials Research and Testing (BAM). The Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH is project sponsor.