Containers with high-level radioactive waste - how long are they safe from a technical point of view? And which container is suitable for which repository? The Federal Office for the Safety of Nuclear Waste Management (BASE) has launched two new research projects under the leadership of the Federal Institute for Materials Research and Testing (BAM). Both projects began in April 2023, and will each run for three years.

“For BASE as the licencing authority, safety is paramount for the disposal of nuclear waste. Even after the last reactors have been shut down, the radioactive legacy must be safely stored, first at interim storage facilities above ground, and then at a final repository in deep geological formations. BASE has launched a research programme that examines the safety aspects of the containers in both areas," says Jochen Ahlswede (in German), head of the Research and International Affairs Department at BASE. The promotion of young scientists will also play a role in the projects.

"The safe interim storage of high-level radioactive waste over many decades puts very high requirements on the materials of the transport and storage containers," says Dr Holger Völzke, head of the Department for Storage Container Safety at BAM. "For this purpose, we are investigating, for example, the long-term resistance of the seals to evaluate them for an extended interim storage of more than 40 years. We are also developing requirements and test criteria, which we can use as a benchmark for developing and testing the containers for final storage

Containers remain in interim storage for several decades

Currently, high-level radioactive waste accumulated in Germany is stored in transport and storage containers at 16 German interim storage facilities. The containers are licensed for interim storage for 40 years. The first licences will expire in 2034, and thus before a final repository is available. The operators will therefore have to apply for new licences in good time.

The aim of the research project entitled "Extended long-term investigations of metal seals using continuous force measurement in the compressed state" is to gain additional knowledge about the extent to which the transport and storage containers will continue to safely enclose the high-level radioactive waste over longer periods of interim storage. The focus is on the metal seals of the containers. In this research project, the metal seals are exposed to various thermal and mechanical loads over longer periods of time, and in specially developed test devices. Improved prognosis models for their long-term behaviour can then be developed with the help of the measurement data thus obtained.

"However, one thing is clear: interim storage facilities and the containers stored therein can only guarantee the necessary protection of humans and the environment for a limited period of time. In the long term, the high-level radioactive waste must, in any case, be safely stored in a repository in deep geological formations," explains Ahlswede.

Container system is an important component of the repository

Which repository container is suitable for which rock type of the future geological repository? This is the question investigated by the research project entitled "Specification of requirements for repository containers and development of test concepts". It entails the identification of various requirements that the containers in rock salt, clay or crystalline rock must meet to fulfil the necessary safety functions. The question of which type of rock will be chosen to host a repository in Germany will be carefully answered by means of an elaborate selection procedure, which is based on the Site Selection Act. Suitable container concepts as an essential component of the possible repository concepts must therefore already be developed in the course of the site selection procedure.

The second research project specifies the requirements for the containers themselves, and also develops possible testing and evaluation standards, which can help to decide which container design will ultimately be the most suitable. The researchers will also consider the international development of container concepts.

BASE will evaluate and publish the compiled findings with regard to safety issues in interim and final storage. The final reports of the two projects will be publicly accessible as an open access publication.