Effect of high dose helium ion irradiation on the surface microstructure of a new neutron multiplying Be−W alloy

A neutron multiplier must be employed to obtain the proper tritium breeding rate and ensure the self-sustaining combustion of deuterium and tritium in fusion reactors, which represents a new and powerful solution for the energy problem. Several researchers have proposed the use of beryllium, an outstanding nuclear metal, as a promising solid neutron multiplier in the helium-cooled ceramic breeder (HCCB) test blanket module (TBM) of the Chinese TBM program. In this module, beryllium will be subjected to high-dose irradiation with high-energy neutrons during services in reactor to produce a large number of helium ions and significant irradiation damage resulting in extreme performance degradation. Unfortunately, the metal’s low melting point and poor irradiation swelling resistance at high temperatures limit its usage in the DEMO reactor. Thus, finding or developing a new neutron multiplier with a higher melting point and better ability to resist irradiation swelling than beryllium in advanced fusion reactors is an important undertaking. Knowledge of the characteristics of the microstructural changes of beryllium and/or beryllium alloys under irradiation is an important factor contributing to the understanding of the degradation of their physical-mechanical properties. In this study, a new beryllium tungsten alloy (Be₁₂W) with a high melting point was proposed and fabricated by hot isostatic pressing. The phase composition and surface structure of Be₁₂W were then analyzed by X-ray and scanning electron microscopy. The Be₁₂W alloy was irradiated with 30 keV He⁺ ions at room temperature at a dose of 1×10¹⁸ ions·cm⁻² and ion fluence of 0.2 μA. Microstructural changes and the types of helium gas-filled blisters that developed on the surface of the alloy after irradiation were subsequently investigated. Blisters with an average size of 0.8 μm and in-plane number density of 2.4×10⁷ cm⁻² initially develops, followed by blisters with an average size of about 80 nm and in-plane number density of 1.28×10⁸ cm⁻².