Planning the future development of nuclear power generation requires studies into the assessment of economic efficiency of nuclear power plants in comparison with other types of power plants and that such studies should be based on reasonable technical and economic indicators (TEI). Despite the importance of the problem and the availability of numerous studies on the subject, the results of such assessments are associated with inhomogeneous and uncertain inputs having a large spread of values, which influences the choice of the best-suited option for the development of the power generation mix and, consequently, the development of the power generation industry. In order to enable more informed decisions for nuclear power industry development, the TEI need to be further refined. This paper analyses the cost structure of nuclear power plants (NPPs) generally accepted in global practice. A study of capital investments in Russia and abroad is made and its outputs serve as the basis for a comparative evaluation of the efficiency of NPPs and gas-fired fossil fuel power plants, taking into account the environmental factors. When considering a conventional approach to evaluating the efficiency of different types of power plants it appears that combined cycle power plants (ССPP) are far more preferable than NPPs. Additional factors are considered, including the impact on the environment, handling and storage of spent nuclear fuel contributing to the cost of nuclear power, as well as decommissioning costs. The additional factors considered for CCPPs are limited to the emissions of carbon dioxide (CO2) which are recognized as the most sizable ones and are subject to quotas unlike other indicators. With the additional aspects fully weighed and taken into account, nuclear and fossil fuel power plants become comparable in efficiency.