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Variation in the surface morphology of polycrystalline UO$$_{2}$$ powder induced by helium precipitation

Serizawa, Hiroyuki  ; Matsunaga, Junji*; Shirasu, Noriko  ; Nakajima, Kunihisa  ; Kashibe, Shinji*; Kaji, Yoshiyuki  

This report addresses the precipitation of helium in polycrystalline UO$$_{2}$$, which deforms the morphology of the grains and their surfaces Helium was injected into pulverized UO$$_{2}$$ particles at 1473 K by hot isostatic pressing (HIP). The specific surface area measured by volumetric gas adsorption instrument implied that small pores should exist on the as-helium-treated sample surface. Field-emission scanning electron microscopy observations showed that numerous shallow basins (approximately 500 nm in radius) with hexagonal fringe were formed on the surface. The basin resembles a ruptured blister whose lid has been forced open. SEM observations showed a uniform polygonal-shaped section of the gas bubble on the fracture surface; this implies that precipitated helium forms a negative crystal in the grain.

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