PREPARATION AND PROPERTIES OF LOWER DENSITY UO$sub 2$ PELLETS.

Studies on low-density UO{sub 2} pellets showed that three methods will produce pellets with the required density range between 9.8 and 10.3 g/cm{sup 3}. These methods are: UO{sub 2} powder with reduced sintering activity; UO{sub 2} powder with UO{sub 2} returns; and UO{sub 2} powder with the addition of ammonium uranyl carbonate. Pellets produced by the first two methods had a large percentage of open pores, while those of the last method all had closed porosity. On isothermal annealing, the percentage of open pores of the first two methods decreased or disappeared. The structures from the three methods differed in a characteristic manner in respect of pore size distribution and pore morphology. On plastic deformation the major part of the porosity remained available for matrix swelling.