EFFECTS OF PELLET MICROSTRUCTURE ON IRRADIATION BEHAVIOR OF UO2 FUEL

In-reactor tests and post-irradiation examinations (PIEs) were perform ed for standard and large-grained pellets with and without additives b eing soluble in a matrix and/or precipitated in a grain boundary, to c onfirm the effects of large grain structure on decreasing fission gas release (FGR) and swelling and to evaluate the influence of the additi ves in the matrix/grain boundary on them. The standard and large-grain ed pellets were loaded into small-diameter rods equipped with a pressu re gauge. These rods were irradiated to about 60 GWd/t U at a linear h eat rate of about 30-40 kW/m in the Halden reactor and then subjected to PIEs. Large-grained pellets showed a smaller FGR compared with stan dard pellets. Post-irradiation annealing tests suggested that swelling during transient power was decreased for large-grained pellets, excep t for those with additive enhancing cation diffusion. (C) 1997 Elsevie r Science B.V.