Nuclear energy is a very important thermal energy source. As the cost of conventional sources of energy (i.e., coal, lignite, and fuel oil) increases, nuclear energy becomes the primary alternative. Many nuclear power reactors are in operation and most are built for the single purpose of producing electrical energy. According to the Rankine cycle process, ∼60% of the heat produced in a reactor core is released into the atmosphere as waste heat. Obviously, this unused energy decreases total thermal efficiency and increases the cost of generating electricity. The minimum possible investment necessary for an existing plant to utilize its waste heat is investigated.