Energy demand has increased in recent decades because of gradually increasing energy needs of our society. Urbanization, industrialization and population growthare only some of the reasons rising energy demand.There are also some rapidly developing states with great energy needs.Because of its importance in our lives it is necessary to ensure energy security.However, the combustion of fossil fuels used for the energy production burdens impacts of climate change. Climate change is mainly caused by human activities. The energy industry is one of the greatest causes of air pollutionbecause of CO2emissions, water pollution and global warming. Extreme weather events take placebecause they are the result of climate change. In addition, many people suffer from health problemscaused by pollution. In order to prevent negative health and environmental impacts of climate change, alternative energy resources have to be exploited. Nuclear energy is one of these alternative solutions. It is a form of clean energy with low greenhouse gasemissions. Except from the environmental challenges, nuclear energy can cope the challenge of energy security. It can produce a great amount of energy by a small amount of fuel. It isclaimed that its low fuel costmakesnuclear energy competitive, although it has high investment costs.Despite its advantages, great concerns delay the expansion of nuclear energy. There are significant risks for the environment and public health in case radiation is released because of a nuclear accident. The three great nuclear accidents(Three Mile Island, Chernobyl, Fukushima Daiichi) had devastating impacts and defined public acceptance of nuclear energy. Nuclear waste management is also one of the problems that has to be settled. Furthermore, the proliferation of nuclear weapons causesfear to public opinion. Concerns for international peace and stability rise.There are contradictory opinions whether their proliferation benefits or not international community. These concerns affect nuclear energyexpansionbecause of fear and stress they cause.In the present dissertation the position of nuclearenergy in the energy mix is examined, as clean energy policies are adopted. In chapter 1, the issue of energy security and the impacts of climate change in our livesare examined. In chapter 2, there are references to uses of nuclear energy, its economy and its position in global energy mix. In chapter 3, the advantages and disadvantages of nuclear energy by an environmental aspect, are mentioned. In chapter 4, the greatest concerns of the nuclear energy expansion, thus nuclear accidents, nuclear weapons and nuclear terrorism, are described. Finally, in chapter 5, the example of China is presented, in order to examine if nuclear energy is apreferable alternative energy resource.