State of play: Accelerator-driven Transmutation of High-level waste

Pretreatment of waste by partitioning and transmutation (P&T) is repeatedly mentioned in connection with the search for a deep geological repository for high-level radioactive waste from the civilian use of nuclear energy. This approach promises to significantly reduce the requirements and risks associated with a - still necessary - final repository.

Partitioning separates spent fuel into different material streams such as uranium, plutonium and minor actinides. Selected radionuclides are then converted into other (radio)nuclides by nuclear physical transformations, in particular by nuclear fission (transmutation).

The idea of partitioning and transmutation as a technological solution to the challenge of radioactive waste management is not new. It was proposed decades ago. For various reasons, it has not yet been implemented. Then, as now, the question was not only one of technical feasibility, but also one of potential benefits. Nevertheless, the idea of using accelerator-driven systems to transmute certain components of high-level radioactive waste has recently received new impetus.

To implement a transmutation cycle, suitable fuels, irradiation facilities and reprocessing technologies are required. One possibility is a subcritical, lead-cooled system with appropriate reprocessing and fuel fabrication processes. Looking at the individual components, it is particularly interesting to see how the concept has evolved since the original proposals and what approaches have been proposed to solve known problems. However, there is still a lack of experience with the operation of subcritical systems and the use of lead as a coolant. There has also been little progress in the area of fuel fabrication and qualification with high minor actinide content. The necessary separation technology is also not yet available on the required industrial scale.

At the same time, the benefits of a large-scale P&T approach are still unclear at best. There is no doubt that a repository for high-level radioactive waste is still needed. Some of the promised improvements could be achieved independently of a possible transmutation scheme, provided that the associated drawbacks are accepted. The fundamental problem of certain long-lived radionuclides, the safe containment of which must be ensured, remains according to the present state of science and technology.