MICROSTRUCTURAL INVESTIGATION OF HELIUM AND LITHIUM EFFECTS IN V-TI ALLOYS IRRADIATED IN FFTF BY MEANS OF B-10-DOPING

To study the effect of helium and lithium on cavity formation for V and V-Ti alloys in a fission reactor, V, V-5Ti and V-20Ti (both doped and undoped with 0.014 B-10) were irradiated at 365-degrees-C to 14 dpa (below-core) and at 406/520-degrees-C (level-2) to 42.5 dpa in the FFTF/MOTA. The He/dpa ratio was estimated to be about 22 at 365-degrees-C and 5 at 406 and 520-degrees-C. TEM observations following irradiation indicated that helium and lithium had little effect on swelling in the specimens. Cavity growth was assisted by helium in V-Ti alloys, though the number density for cavities was rather low compared to that of undoped alloys. Agglomeration of small dislocation loops, designated as "rafts", was the main feature observed in V-5Ti, whereas tangling of dislocations was predominant in V-20Ti. Halos containing many cavities were formed around boride precipitates only in V-20Ti-0.014 B-10 at 520-degrees-C, and arose from the effect of lithium.