Optimal power grid development has a special place in countries' planning. WASP software was developed by order of the International Atomic Energy Agency to model, design and compare the production capacity of various thermal and hydro power plants and by using long-term probabilistic modeling, with greater depth and accuracy than other models in a specific capacity period. Provides the required types of power plants in different years. The purpose of this article is to compare the economics of thermal and nuclear power plants. For this purpose, the cost price of each kilowatt of electricity produced by different power plants is modeled and compared. Sensitivity analysis on major parameters shows that the choice of nuclear capacity is highly sensitive to the price of natural gas, discount rate and construction cost. Sensitivity to maintenance costs is moderate and low relative to the price of nuclear fuel. The results of the study show that from the point of view of the national economy, the decision to build about 14,000Mw of nuclear power at the end of the 30-year period of nuclear power plants development has economic justification according to political conditions and international interactions. The best option for the construction of a nuclear power plant is the construction cost of 1,100$/KW, the fuel rate of 4.5$/Mwh and the maintenance cost of 35$/KWyear. In the worst case (long manufacturing period and high discount rate), if the price of gas is 20cents/m3 or more, it has the most economic justification.