Matrices for waste streams immobilization

The ASOF project (Advanced Separation for Optimal management of spent Fuel) investigates the development of new techniques for the separation, conversion and conditioning of irradiated spent nuclear fuel and the related waste management aiming at an optimization of the disposal concepts. In the followed approach U, Pu and the minor actinides would be recycled or transmuted. One of the objectives is to study the added value of extracting Cs and Sr from the reprocessed waste stream and of immobilizing these fission products, responsible for heat generation, in a durable matrix, which needs to be stored for at least a century in a cooling facility to have a significant reduction of the thermal output. The waste remaining after the extraction of Cs and Sr would then be immobilized in a waste form of category B instead of category C (heat emitting). Many types of matrices such as glass, glass ceramic, ceramic, crystalline ceramic, or alkali-activated material can immobilize radionuclides. This state-of-the-art report presents an overview of the possible waste forms, based on a literature study. It was written in the framework of ASOF WP3, Conditioning of waste groups originating from a partitioning scenario. The focus is on the immobilization of Cs and Sr, but most waste forms can be also used to immobilize the radionuclides of the rest fraction. Some technologies that can be used to produce the waste forms are also described, with a focus on the hot isostatic pressing process, which is a promising technology allowing an important volume reduction.