Pure Fe and Fe–15Cr single crystals with three different orientations, ,  and , were irradiated in the BR2 reactor of SCK-CEN, at a temperature of 300 °C to a dose of 0.2 displacements per atom. Irradiation-induced microstructure changes were studied by transmission electron microscopy. The size distribution and defect densities were measured and the Burgers vectors and the nature of the loops were determined in detail. In the pure Fe specimens, mainly ah100i edge-type interstitial dislocations loops could be identified. Their average density and size were (4.1 ± 0.4) x 10^21 m^-3 and (8 ± 2) nm, respectively. In Fe–15Cr, on the other hand, no defects could be observed.