DEFECT PRODUCTION AND ACCUMULATION UNDER HYDROGEN AND HELIUM ION IRRADIATION

The 316L stainless steel (316L SS) is a candidate material for the fir st wall of a fusion reactor, which will be irradiated with 14 MeV neut rons and escaped ions. This will produce helium and hydrogen in the ma trix, which come both from the transmutation production and escaped io ns of the plasma. The synergistic action of high-energy cascades nad h elium induces important damage, such as swelling, blistering and heliu m embrittlement. The hydrogen combines with the radiation defects to p roduce dense tiny bubbles (or voids) and substitutes for gaseous impur ities (such as soluted oxygen, nitrogen, sulfur and phosphorus) which react with other composites Fc. Cr, Ni and Mo to form new phases. such ns Cr2O3, (CrFe)(2)O-3, (Fe3C2)28N, (CrMo)N, (Fe2Mo)12H and (FeNi)(9) S-8. These induce mechanical property changes. The hydrogen combined w ith helium and high energy cascades will induce mure serious damage th an that of helium alone. To exhibit the synergistic action of helium a nd hydrogen, the 316L SS specimens were bombarded with helium, hydroge n and mixed ion beam with energy ranging from 27 to 38 keV Eo ii dose of 10(17)-8 x 10(18) ions/cm(2) at 573 K. The results indicate that (a ) for the helium ion irradiation, the threshold dose fur blistering in thr energy range 27-100 keV is higher than that for the 1.0 MeV heliu m ion irradiation. The surface effects play an important tote in the b listering. (b) When specimens bombarded with the mixed bi am of helium and hydrogen ions of 27 keV reached the same helium dose (6.4 x 10(17 ) He+/cm(2)), the diameter and density of bubble on surface increase a t a ratio of the hydrogen to helium increase. The more hydrogen ions i mplanted, the easier and more serious the blister is. (c) When the kin etic energy of the mixed beam decreases in the range 10-30 keV, the ac tion of hydrogen ions on the blistering appears more evident. It seems that the hydrogen plays an important role in bubble formation and gro wth. (C) 1997 Elsevier Science B.V.