Last 50 yrs the conventional Nuclear Power (NP) witnessed several periods of optimistic expectation for NP growth. Nevertheless, no one scenario was completely realized, and periods of high expectation followed by NP stagnation. Apparently, this proves that not only economic but also social and geopolitical environment is at least not fully favorable to the conventional NP. Being nuclear, an Emerging Nuclear System (ENS) inherits this unfavorable environment. The ENS should therefore cope with the sigma of nuclear past and a potential dark side of nuclear future. The paper reviews several international studies of the global nuclear legacy performed last decade and the implication of the legacy on generic perspective of NP. Further, the paper identifies and discusses unresolved problems of nuclear fuel cycle, which can feed threat of proliferation and emerging face of nuclear terrorism. Finally, the paper formulates some recommendations that would help proponents of emerging nuclear energy systems to govern identified problems and thus helps to embed NP in sustainable development.