Primary factor in determing the shape of image crystal

Serizawa, Hiroyuki  ; Oishi, Yuji*; Haga, Yoshinori   ; Yamanaka, Shinsuke*; Tsuru, Tomohito   ; Kaji, Yoshiyuki  ; Matsunaga, Junji*; Kashibe, Shinji*

We found that porous UO grain was formed by the precipitation of helium injected by HIP. SEM analysis showed that polyhedral negative crystals were formed in the sample. The shape of the negative crystal changes dramatically with the conditions of helium precipitation. A truncated octahedron-type, an octa-triacontahedron and a pentacontahedron-type negative crystal were observed. The change in the precipitation condition means the variation in the activity of helium in matrix. So, our study implies that the shape of the negative crystal should changes depending on the helium inner pressure enclosed in the negative crystal.