Detritiation of JET Beryllium and Tungsten

Abstract

During the operation of a fusion reactor, first wall components are exposed to the plasma and therefore tritium, resulting in generation of tritiated materials that would be classified as intermediate level waste (ILW) following their removal from the vessel. Investigations were undertaken into the thermal treatment of beryllium and tungsten representative of the materials used within the Joint European Torus (JET) fusion reactor to assess if tritium from these materials can be removed in the Material Detritiation Facility at the United Kingdom Atomic Energy Authority. This detritiation process may allow the reclassification of these materials as low level waste (LLW). When heated in the presence of oxygen, both tungsten and beryllium readily oxidize as temperature increases. The oxide layers that are formed on tungsten and beryllium surfaces are thought to act as a tritium barrier, reducing the amount of tritium that can be removed by thermal treatment. As such, the generation of oxide layers may need to be minimized for treatment of tungsten and beryllium, potentially via thermal treatment at lower temperatures. Additionally, the formation of beryllium oxide presents health and safety concerns due to its toxicity and physical form. Experiments were undertaken using tungsten and beryllium samples from previous JET campaigns. The samples were heated in a pyrolyzer, and the tritium released was captured in a series of bubblers. The remaining tritium in the material was characterized by acid dissolution to allow for detritiation factors (which are defined as the fraction of tritium inventory in the sample before and after the thermal treatment) to be calculated. Tritium was successfully removed from the samples by thermal treatment in air. Future trials will use samples with larger tritium inventory to confirm obtained results and demonstrate the feasibility of thermal treatment as a detritiation method for tungsten and beryllium on higher-activity samples. This should allow for samples representative of the JET ITER-like wall (current JET configuration) to be detritiated and could demonstrate the ability of the process to reduce the tritium inventory of JET materials and allow reclassification of components from ILW to LLW.