Microstructural evolution in UO under accumulation of ion tracks by high energy fission products

Sonoda, Takeshi*; Ishikawa, Norito   ; Sataka, Masao; Sawabe, Takashi*; Kitajima, Shoichi*; Kinoshita, Motoyasu*

Microstructural evolutions of ion-irradiated UO were observed by use of a 300 kV FE-TEM and a FE-SEM at CRIEPI. For understanding the effects of accumulation of ion tracks in UO, 210 MeV Xe+16 ions irradiation up to a fluence of 1.5 e16 ions/cm were done. At a fluence of 5e14 ions/cm (overlapping num. of tracks: 1e2), elliptical changes of fabricated pores and the formation of dislocations are started. Over 1e16 ions/cm (overlapping num. of tracks: 2e3), the grain sub-divisions are observed and the dislocation density does not tend to increase. These drastic changes in UO indicate that the overlapping of ion tracks will cause the point defects, enhance the diffusion of point defects and dislocations, and form the sub-grains at relatively low temperature.