Current Status of Beryllium Materials for Fusion Blanket Applications

Beryllium is a promising functional material for several breeder system concepts to be tested within the experimental fusion reactor ITER and, later, implemented in the first commercial demonstration fusion power plant DEMO. For these applications its resistance to neutron irradiation and the detrimental effects of radiogenic gases (helium and tritium) is crucial for fusion reactor safety, subsequent waste management and material recycling. A reliable prediction of beryllium behavior under fusion irradiation conditions requires both dedicated experiments and advanced modeling. Characterization of the reference and alternative beryllium pebble grades was performed in terms of their microstructure and tritium release properties. The results are discussed with respect to their application in fusion blanket systems. The outcomes from the HIDOBE-01 post irradiation experiment (PIE) are discussed to highlight several interesting features manifested by beryllium irradiation at fusion relevant temperatures. Titanium beryllide is presently developed as a possible substitute for beryllium pebbles as it shows better oxidation resistance, higher melting temperature and tritium release efficiency. Pebbles consisting predominantly of Be₁₂Ti phase were successfully fabricated at Rokkasho, Japan. Recent advances in modeling provide new insights on the production of point defects and the behavior of helium and hydrogen impurities in beryllium, improving understanding of the mechanisms of primary damage production, hydrogen's effect on the size and the shape of gas bubbles, and tritium removal from the pebbles. The relevance of the experimental and modeling results on irradiated beryllium for the design of a fusion demonstration reactor is evaluated, and recommendations for future R&D programs are proposed.