As energy issues are at the top of the policy agenda worldwide, policy-makers increasingly need better decision-supporting processes to assist them in fostering a sustainable energy future. This paper reflects on the interpretation of sustainable development, and links these reflections with the theory and practice of impact assessment applied on energy issues. An analysis of existing impact assessment approaches with regard to their contribution to sustainable development leads to a set of principles for 'sustainability assessment'. Through a study of a participatory impact assessment supporting the development of a radioactive waste management plan in Belgium, the interpretational limits of sustainable development in a nuclear energy context are discussed. This paper sheds light on the complex context in which impact assessment exercises must contribute to sustainable energy development, with a focus on the nuclear energy-(un)sustainability nexus. (C) 2011 Elsevier Ltd. All rights reserved.