Аt least in the last decade and a half the EU has put strict priorities on decarbonisation and development of carbon-free technologies (mostly based on renewable energy resources) in its energy policy. Achieving this goal consists a challenge for many member-states from Central and Eastern Europe (CEU). That formed a tendency for this countries to defend nuclear power as a tool of decarbonisation. So this countries becomes a "nuclear flank" of the EU and has itd influences on forming outlines of energy and climate policy of the Union. The article describes the origin of nuclear power sector in the countries of the region and basic challenges for the sector during postsocialist transit and EU accesion. This challenges were overcome in building partnership with the players of world nuclear industry. In the same time lasting dependency from russian (soviet) nuclear technologies and general distrust of the EU toward the nuclear projects financed by Russia formed an obstacle for several ambitious projects. Countries of the CEU also coordinated their positions on the role of nuclear sector in the decarbonisation and tried to find poweful allies within the EU (France) to defend their stance.