Hydrogen isotopes behavior in nickel in nuclear fusion reactor conditions

The behavior of hydrogen isotopes in metals is very important for future nu clear fusion reactors. To study deuterium influence on helium pre-irradiate d nickel, 0-28 MeV He2+ and 7 MeV D+ beams were used. The He samples pre-im planted at 30, 100 and 300 appm (atomic parts per million) D+ (10(18) ions/ cm(2)) irradiated and annealed (1273 K) in high vacuum for 1, 10, 100 and 1 000 h. After an electrochemical preparation (Struers jet), they were examin ed by transmission electron microscopy (TEM). Values for He bubble radii an d densities depending on He ions doses and annealing periods are reported. Two types of bubbles were observed, namely: "small" bubbles, predominantly in the matrix (from 5 nm radius for 30 appm, 1 h annealing to 35 nm for 300 appm, 100 h annealing), and "large" bubbles, predominantly in the grain bo undary regions, but even in some dislocations (from 30 nm radius for 30 app m, 1 h annealing to 120 nm for 300 appm, 100 h annealing). A unique bubble coarsening mechanism - the Ostwald ripening - is considered. The influence of deuterium on the "small'' and "large" bubble radius values is discussed. (C) 2001 International Association for Hydrogen Energy. published by Elsev ier Science Ltd. All rights reserved.