There is no general chapter in the EU treaties on energy, but Art. 3 u TEC quotes energy as one of the fields in which the Union can act to achieve its objectives.
The EU has also power over ("competence") energy policy under the normal community rules for the development of the internal market, trans-european networks, the social and economic cohesion and environmental policy.
Notes
Nuclear energy is part of the Euratom Treaty.
The future
The EU Constitution proposes that energy become a shared competence - EU law would therefore suppress member states' existing legislation and right to legislate in this area. The choice of energy source will remain a national competence.
The EURATOM Treaty will be annexed to the Constitution as a protocol, even though it would cease to be in force in 2007 if not renewed. The treaty promotes the use of nuclear energy, but neither the existing treaties nor the proposed EU Constitution can force countries to accept nuclear power plants in their territories.