The Effect of Radiation Damage and Helium on Hydrogen Trapping in Beryllium

Abstract

The beryllium is a candidate material for the ITER- first wall. At neutron bombardment radiation defects and helium retention, as a result of nuclear reaction ⁹Be(n,2n) → 2He+ 94 keV. will take place. The investigation of radiation defects and helium affect on hydrogen retention in beryllium were carried out. The beryllium samples were irradiated by 2.8 MeV He ions in Van de Graaf accelerator at the temperature 773 K to simulate neutron irradiation. Helium irradiation fluences were lower than blister formation critical dose and were equal 10²⁰, 5 10²⁰ and 10²¹ He⁺/ m². After that 3-keV H⁺ ions were implanted into the samples at temperature 573 K. Hydrogen irradiation doses were 5-10²² H⁺/m² and 10²³ H⁺/ m². The microstructure of the samples was investigated after He⁺ and after He⁺ and H⁺ irradiation. Depth distribution profiles was measured using the elastic by recoil detection technique. The integral hydrogen concentration in beryllium with He⁺ ions induced defects was 2.6-2.8 times large then that in beryllium non-irradiated by He⁺ ions. For specimens depth previously irradiated by He⁺ ions peak in the hydrogen distribution was at about 0.15 μm in comparison with to the place ~ 0.03 μm for specimen implanted only with 3 keV H⁺ ions simultaneously. The joint irradiation by He⁺and H⁺ ions results in small blisters formation. At maximal He⁺ fluence (10²¹ He/m²) the blister caps are broken, hydrogen releases and integral hydrogen content decreases. The observed effects are explained by vacancies and He atoms diffusion and hydrogen trapping by vacancy-helium traps.