Helium swelling behavior for neutron multipliers after irradiation with He ions at high temperatures

Abstract

Beryllides as beryllium intermetallic compounds are the advanced multiplier materials as candidate materials for fusion demonstration power plant (DEMO) due to having good properties such as low swelling rate and stable chemical properties.Under DEMO operation environment, the generated He amounts in beryllium are estimated around 20,000 appm He. This study was evaluated the effect of He fluence and irradiation temperature on the bubble behaviors in Be12Ti and beryllium. The irradiation of He ion was carried out using an In-situ transmission electron microscope equipped with an ion gun by implantation up to 25,000 appm He. For comparison, beryllium was carried out in similar experiments.Bubbles were observed in Be12Ti at 873 K after the implantation of 15,000 appm He, while in Be at the same temperature, their appearance occurred post-implantation of 4,500 appm He. In addition, growth of bubbles in beryllium was observed with increase of He ion fluence. Sizes and densities of bubbles in Be12Ti and beryllium were evaluated irradiated in 25,000 appm He at 673 and 873 K.In the case of Be12Ti, fine bubbles were observed in a high density state, and it was found that the swelling rate was a few percent. By contrast, bubbles in beryllium had a diameter in the range from tens to several tens nanometers, and growth of these bubbles were observed. The swelling rate of beryllium was approximately 18 %.