Abstract: Abstract: A comparative exergoeconomic analysis is reported of waste heat recovery from a Gas Turbine-Modular Helium Reactor (GT-MHR) using various arrangements of Organic Rankine Cycles (ORCs) to produce electrical power. The organic Rankine cycles considered are: a simple Organic Rankine Cycle (SORC), an ORC with an internal heat exchanger (HORC) and a regenerative Organic Rankine Cycle (RORC). The exergoeconomic analysis is performed based on the specific exergy costing (SPECO) approach. For this purpose, the combined cycles are first analyzed thermodynamically from both energy and exergy perspectives. Then cost balances and auxiliary equations are applied to subsystems and exergoeconomic parameters are calculated for the components and the overall combined cycles. Based on fixed operating conditions for the GT-MHR cycle, the three combined cycles are compared. Finally a parametric study is performed to ascertain the effects on the exergoeconomic performance of the combined cycles of such significant parameters as compressor pressure ratio, turbine inlet temperature and evaporator temperature. The results show that the GT-MHR/RORC achieves the lowest unit cost of electricity produced by the ORC turbine, while the highest unit cost of electricity is observed for the GT-MHR/HORC. In addition, the exergy destruction cost rate is found to be highest for the GT-MHR/RORC and lowest for the GT-MHR/HORC.