Reduction of the open porosity of UO2 pellets through pore structure control

Abstract A powder mixture was prepared by mixing uranium-dioxide (UO 2 ) powder ex-AUC with its milled powder and was pressed into compacts. The UO 2 pellets were sintered under hydrogen. The compact density increased with the content of milled powder, since the particles of the milled powder might fill the interstices between the particles of the UO 2 powder ex-AUC during pressing. A mechanism for the formation of flake-like pores was proposed on the basis of the microstructures of the powder, the compact, a partially sintered pellet and a final pellet. The open porosity of a sintered pellet decreased with increasing content of the milled powder, and the reduction of open porosity could be mainly attributed to the decrease in the number of flake-like pores whose shapes deviate greatly from roundness.