Depth profiles of damage accumulation in UO2 and (U,Gd)O-2 pellets irradiated with 100 MeV iodine ions

To study the initial defect formation and accumulation process during fissi on events, sliced pellet specimens of UO2 and (U,Gd)O-2 were irradiated at ambient temperatures below 200 degrees C, with 100 MeV iodine ions over a f luence range of 1.0 x 10(18) - 2.0 x 10(19) ions/m(2). The surface of the s pecimens was analyzed by scanning electron microscopy (SEM) and X-ray diffr actometry (XRD), and then the depth profiles of incident iodine ions and de fect clusters were measured by secondary ion mass spectrometry (SIMS) and t ransmission electron microscopy (TEM), respectively. Lattice parameter chan ge, which is associated with point defect accumulation, increased with ion fluence. Defect clusters of dislocations and dislocation loops were recogni zed, and their depth profiles were in good agreement with the calculated da mage profile. These profiles of iodine ions and dislocation loops in both U O2 and (U,Gd)O-2 were discussed in terms of inelastic and elastic collision s. (C) 1999 Elsevier Science B.V. All rights reserved.