AbstractThe behavior of hydrogen isotopes in metals is very important for the future nuclear fusion reactor. To study deuterium influence on helium pre-irradiated nickel, 0–28 MeV He++ and 7 MeV D+ beams were used. Thirty, 100 and 300 appm He pre-implanted samples were D+ (1018 ions per cm2) irradiated and 1, 10, 100 and 1000 h high vacuum annealed (1273 K). After an electrochemical preparation (Struers jet), they were examined by transmission electron microscopy (TEM). Values for He bubbles’ radii and densities depending on He ions’ doses and annealing periods are reported. Two types of bubbles were observed: ‘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 boundaries regions, but even in some dislocations (from 30 nm radius for 30 appm, 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’ bubbles’ radii values is discussed.