Nuclear energy has been long considered by policy makers as a low carbon energy source. However, current trends in national policies indicate threats to nuclear energy’s favoured position as a preferred driver of clean energy transition. This thesis aims to examine the status of nuclear power in the energy transition policies in France, Germany and the UK. It investigates the legal and policy framework for nuclear power as directed by the Euratom Treaty and the Lisbon Treaty. The work also investigates decommissioning of nuclear plants in three European countries (France, Germany, and the United Kingdom (UK) in the context of their liabilities and obligations. Two of these (France and Germany) are Member States of the European Union (EU) and the UK, is a former Member State. The thesis uses comparative and historical methodology to critically consider international covenants, the multi-national aquis of the EU (which body of law holds legal primacy across the bloc), and both national legal and policy frameworks to explore nuclear energy’s potential role in the energy transition. The work also investigates the role of state in a liberalised EU market for promotion of nuclear energy as a clean source of power. The works finds out that EU law does not bar adoption of preferential national choice in favour of nuclear power, and the recent jurisprudence on the EU competition law also permits Member State measures to adopt nuclear power as a preferential source of energy subject to their compliance with both EU state-aid rules and environmental law.