The influence of trivalent dopants (rare-earths, RE) on the structure, composition and electrochemical reactivity of UO2 has been investigated using scanning electron microscopy (SEM/XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and cyclic voltammetry (CV). This was achieved by comparing the behavior of undoped UO2.002, a slightly doped 1.5 at% SIMFUEL, and two rare-earth doped 1102 (6 wt% Gd-UO2 and 12.9 wt% Dy-UO2) specimens. The reactivity decreased in the order UO2.002 > SIMFUEL > Dy-UO2 > Gd-UO2, showing that this decrease is a consequence of RE Ill doping. Raman spectroscopy showed this could be attributed to the formation of REIII - oxygen vacancy clusters whose formation decreases the availability of the vacancies required to accommodate the injection of oxygen interstitials during anodic oxidation. The behavior of SIMFUEL is complicated by the simultaneous formation of REIII- oxygen vacancy clusters and Zr-O-8 clusters. (C) 2013 The Electrochemical Society. All rights reserved.