Energy security has been implemented by the nuclear energy for the last 30 years in South Korea. S Korea still requires the ambitious plan to sustainably supply inexpensive and domestic or semi-domestic energy regardless of the geo-political instability around the world. Even though the national Government supports all endeavors to actively introduce many different green energy resources such as solar and wind power in S Korea, still nuclear energy is the practical option to meet the national energy challenges. For the last three decades S Korea has enjoyed the stable supply of SEU from major international suppliers. However, that does not necessarily mean the stable long term supply for new reactors to be deployed in the future in S Korea for the rest of their life time. In addition, S Korea has experienced social tensions over the issues of radioactive waste management including used nuclear fuel. In the short term, the proper at or away from the reactor site storage option is the best approach to management used fuel. But in the longer term, proliferation resistant recycling of used fuel which can assure the stable supply of fresh fuel to the nuclear energy system while minimizing the burden of final disposal will be the best measure for S Korea which becomes one of the world leaders in the nuclear industry. To accomplish that mission, it is important to focus on the fundamental but innovative research on used fuel recycling which can ensure the safety, security, and safeguardability of the fuel cycle system. In addition, especially after the Fukushima event, it is highly recommended to review what would be the optimum option for future energy in S Korea and the best way for the technology development to accomplish it throughout active dialogues among stakeholders domestically and internationally.