Technical and economic analysis of a pebble bed modular reactor with nitrogen coolant

High-temperature nuclear reactors (HTR) could benefit from using the gas turbine in tandem with a steam turbine; this is the principle of combined cycles using natural gas. HTRs have the characteristic that the turbine works in high-temperature conditions. The flue gas could feed a steam generator to produce additional electricity improving system efficiency. The current study assesses the likeliness of having a combined cycle from a Pebble Bed Modular Reactor using nitrogen as a coolant. The balance of the plant and the corresponding configuration to meet this goal are given; the results show an efficiency of 53.56% of electrical generation compared to 42% reported by the HTR-PM. The share cost for turbine plant equipment represents 8.9%-14.0% of the total cost of the power plant. Three scenarios are contemplated to assess the economic impact of the additional generation where an increase in the overnight cost is considered, 9.99%, 12.41%, and 15.73% because of the additional cost of the steam turbine and associated equipment. Assuming a 4500 US$/kW cost for installed capacity for the HTRPM reactor, for a 10% discount rate, the electricity total levelized cost is 95.56 US$/MWh. For the proposed combined cycle using nitrogen as a coolant, the electricity total levelized cost is 89.78 US$/MWh, assuming a 10% discount rate when the higher overnight cost is taken into account (5208 US$/kW). Using nitrogen under this alternative will produce an additional electricity production of 425,742 MWh annually. It leads to an electricity cost reduction of 5.78 US$/MWh even in the higher cost for the nitrogen combined cycle here considered, and a 10% discount rate compared with the HTR-PM steam cycle reported data, showing the technical and economic feasibility of using nitrogen as a coolant gas.