Several ways to overcome dependence on fossil fuels/energy sources of petroleum for national energy procurement have been performed, such as replacing petroleum with liquid coal/gas, and other renewable energy such as hydrogen. This has been stated in the Government Regulation no. 79 of 2014 on National Energy Policy and Law no. 17 of 2007 on the 2005-2025 National Long-Term Plan. To support national energy growth, the government has enacted the use of new and renewable energy contributing to more than 23% of total energy consumption and that the use of oil should be reduced to less than 25%. Experimental Power Reactor or called Reaktor Daya Eksperimental (RDE) is built to demonstrate for electricity generation or cogeneration purpose, which utilizes nuclear heat for producing electricity and for providing process heat for an industry, for example desalination. Cogeneration system can also improve the economical benefit of the RDE by thermal utilization. Seawater desalination is an attractive solution, of which the technologies have been well established over the past 50 years. The two most commonly used desalination technologies are multistage flash (MSF) and reverse osmosis (RO) systems. Basically, almost all PLTUs in Indonesia have applied desalination technology to supply the process water needs, but they still use fossil energy to supply heat. In order to overcome electricity deficiency and water scarcity in some areas of Indonesia, then to accommodate a government regulation on energy mix, it is necessary to study nuclear heat utilization for desalination (Nuclear Desalination) through cogeneration system. The Nuclear Desalination is conducted by coupling the RDE with desalination units, so it can simultaneously produce electricity and freshwater. An intermediate heat exchanger is incorporated between the nuclear reactor and the desalination unit to ensure no radioactive contamination in secondary system or to protect the desalinated water. The objective of study is to choose the most optimum options of the steam extraction points that will be used for desalination process. The result of this study showed that heat can be extracted in the heat application line before the steam turbine (coupling option 1) and the downstream of steam turbine (coupling option 2). For coupling option 1, the steam (0.94 kg/s) with the temperature of 520°C can be extracted to produce a 27 m3/h fresh water. Meanwhile, using the low-pressure steam rejected from turbine (coupling option 2), the fresh water of 16.5 m3/h (396 m3/d) flow rate can be produced from the desalination unit.