Gas Turbine-Modular Helium Reactor Research Articles

Performance analysis of stirling engine double-effect absorption chiller hybrid system for waste heat utilization from gas turbine modular helium reactor

In this study, a cogeneration system that consists of a Stirling engine, Double Effect H2O/LiBr Absorption Chiller, and Gas Turbine Modular Helium Reactor cycle was examined. The rejected heat from the Gas Turbine Modular Helium Reactor cycle was used as input energy for both, the Stirling engine and the Double Effect Absorption Chiller to produce additional power and chilled water, respectively. A thermodynamic analysis was performed and optimized for the proposed cycle based on the first law of thermodynamics/energy utilization efficiency. The effects of some parameters were studied, including compressor pressure ratio, turbine inlet temperature, the low-pressure compressor inlet temperature, in addition to the operating temperatures of the Stirling engine and the Double Effect Absorption Chiller. Our results indicate that integrating the two systems into the GT-MHR cycle will increase the energy utilization efficiency by 4.73%−5.46%-points at a turbine inlet temperature range of 700–900 °C. Moreover, the results show that the helium mass flow rate of the combined cycle at the same turbine inlet temperature range is lower than that of the standalone Gas Turbine Modular Helium Reactor cycle by 16.1%−17.78%.

Assessment of thermal performance improvement of GT-MHR by waste heat utilization in power generation and hydrogen production

The Gas Turbine Modular Helium Reactor (GT-MHR) uses two compression stages to compress the helium and a pre-cooler and an intercooler to reduce the compressors inlet temperature, that dissipate around 308.36 MWth at the design operational conditions. This dissipated thermal energy can be used as an energy source to produce hydrogen. An energy analysis is conducted for a proposed system that includes GT-MHR combined with Organic Rankine Cycle (GT-MHR/ORC) and a Proton Exchange Membrane (PEM) electrolyzer (GT-MHR/ORC-PEM) for hydrogen production. The optimum operating parameters values of the new cycle are obtained using the Engineering Equation Solver (EES) software. Thermal efficiency has been improved from 48.6% for the simple GT-MHR cycle to 49.8% for the new combined (GT-MHR/ORC-PEM) cycle including hydrogen production at a rate of 0.0644 kg/s at the same operating conditions. However, the thermal efficiency for the combined GT-MHR/ORC was higher and reaches 50.68%. Moreover, a parametric study is carried out over a wide range of some operating conditions such as turbine inlet temperature, Compressor pressure ratio and compressor inlet temperature to investigate their effect on the new cycle performance. Results revealed that increasing the low-pressure compressor inlet temperature increases the amount of hydrogen produced while decreasing thermal efficiencies for the three cycles. Furthermore, increasing compressor pressure ratio reduces the mass flow rate of hydrogen produced util it reaches a minimum value then it starts to increase slightly, on the contrary, an opposite relationship is observed between thermal efficiencies and compressor pressure ratio. Moreover, at low compressor pressure ratio, the rate of hydrogen produced increases with increasing turbine inlet temperature; however, it decreases by increasing the turbine inlet temperature at high compressor pressure ratio. Nevertheless, a direct correlation is noticed between thermal efficiencies and turbine inlet temperature.

Exergoeconomic analysis and optimization of a Gas Turbine-Modular Helium Reactor with new organic Rankine cycle for efficient design and operation

Gas Turbine-Modular Helium Reactor (GTMHR) is a promising option to meet today’s soaring energy demand. A GTMHR combined with organic Rankine cycles (ORCs) can deliver higher performance. This paper presents an exergoeconomic optimization for a combined system comprising a GTMHR and an ORC where the ORC recovers the GTMHR waste thermal energy. The system performance is optimized using a simulation-based optimization method with simultaneous determination of the design parameters as well as selection of the components and their respective compositions for the ORC working fluid. A parametric study is performed to study the effects of the key design parameters on the system performance. Moreover, an off-design simulation procedure is proposed, and the system off-design performance is analyzed. The results show that R134a (100%), R22 and R143a (11.27% and 88.73%), and R134a and R152a (54.54% and 45.46%) are the best ORC working fluid for low, medium, and high helium temperature cases, and their minimum levelized cost per unit exergy are 8.449 $/GJ, 8.116 $/GJ, and 7.862 $/GJ, respectively. Furthermore, helium temperature and pressure ratio are found to have the most significant influences on the system performance. Finally, it is observed that a combined system with higher design parameters exhibits better off-design performance, namely higher power output and efficiency. Therefore, the GRMHR-ROC system should be designed with a relatively high helium temperature if allowed.

Thermodynamic analysis of a Na-O-H thermochemical cycle coupled to a Gas Turbine Modular Helium Reactor (GT-MHR)

Hydrogen (H2) is considered a clean fuel because its combustion releases heat, water and near-zero carbon emissions. This substance can be produced through many routes, including thermochemical cycles in which water molecules are splited into oxygen and hydrogen through specific chemical reactions supported by an appropriate heat source at specific temperature conditions. There are a wide variety of thermochemical cycles under development, many of them require temperatures higher than 1000°C while others, like the cycles U-Eu-Br, Mg-Cl and Cu-Cl can operate below 550°C. The reduction in the temperature levels of a thermochemical process allows the use of various energy options, facilitating H2 production. So, the main aim of the paper is to analyze hydrogen production according to the Na-O-H thermochemical process whose required heat is supplied by a Gas Turbine Modular Helium Reactor (GT-MHR), a nuclear power plant (NPP) with low cost and low carbon emissions. The Na-O-H is a fresh chemical process that can operates at temperatures close to 400°C. The system will be studied in the software Engineering Equation Solver (EES) according to the first and second laws of thermodynamics. The results indicate that such system can produce around 3.654 kg/s of H2 considering a mass flow rate of 500 kg/s of helium coolant at 850°C coming from GT-MHR.

Energy, exergy, economic and environmental analysis and optimization of a novel biogas-based multigeneration system based on Gas Turbine-Modular Helium Reactor cycle

Biogas for supply of power plants can play a paramount role in reducing greenhouse gas emission and extra cost of a fossil fuel based plants. Regarding this aspect of biogas heat source, a novel biogas-based multigeneration system is proposed and modeled under privilege of first and second laws of thermodynamics, economic, and environmental perspectives. Furthermore, multi-criteria optimization of this integrated system is carried out from 4E (energy, exergy, exergoeconomic, and environmental) analysis standpoints. The introduced multigeneration system is able to produce optimum cooling capacity, heating capacity, net power, distilled water, and hydrogen of 123.59 MW, 0.73 MW, 280.35 MW, 18.14 kg/s, and 0.2432 kg/s, respectively. Under this circumstance, the thermal efficiency, exergy efficiency, unit product cost (UPC) of the system, and environmental penalty cost rate are calculated 72.75%, 50.21%, 6.79 $/GJ, and 168 $/h, respectively. Additionally, among all components, reactor core and among different sub-systems, the gas turbine-modular helium reaction (GT-MHR) cycle has the highest contribution to the overall exergy destruction. Finally, a complete sensitivity study based on key thermodynamic, thermoeconomic, and environmental parameters is performed and results are extended and discussed.

Exergetic evaluation of a conceptual design for hydrogen production and seawater desalination using an advanced nuclear reactor as energy source

In this work, a computational model to develop the conceptual design for hydrogen production and seawater desalination based on a modular nuclear reactor as an energy source is presented. The four-step copper-chlorine (Cu-Cl) process is used to produce hydrogen coupled to the gas turbine modular helium reactor (GT-MHR) nuclear system through a Brayton cycle for the electrical energy generation. A fraction of the thermal energy from the GT-MHR system is used to reach and maintain the temperature requirements in the Cu-Cl process. The rejected heat from the oxy-decomposition reaction is used to desalinate seawater through a multi-stage flash (MSF) process. It is employed a chemical process simulator in order to develop a computational model of the proposed system. The global energy and exergy efficiencies of the proposal are 32.47% and 52.20% respectively, producing 0.2190 kg/s of hydrogen and desalinating 4.9492 kg/s of seawater. It is made an estimate of the cost of hydrogen produced using HEEP®, resulting in 2.77 $/kgH2.

Multi-objective optimization of a combined cycle using exergetic and exergoeconomic approaches

A parametric study is conducted for a combined cycle which combines a Gas Turbine-Modular Helium Reactor (GT-MHR) and two Organic Rankine Cycles (ORCs) to reveal the influences of decision parameters on the performance and total cost of the cycle. Two ORCs are operated from GT-MHR waste heat. Also, in order to optimize the system from both thermodynamic and economic aspects, a multi-objective optimization strategy is applied. The purpose of the optimization is to maximize the exergy efficiency and to minimize the total cost rate of the system. The selected decision variables in optimization process are the compressor pressure ratio, temperatures of inlet turbine and evaporators, temperature difference in the evaporator and degree of superheat at the inlet of the ORC turbines. After optimization, the exergy efficiency reaches 50.20% compared to 49.84% of the base case. Furthermore, it approximately reduces the capital expense by 2.4%. Distribution of the decision variables for the Pareto optimal front reveals that the degree of superheat at the inlet of the both ORC turbines has a tendency of being almost lowest value. However, the other variables reveal contrast process on the exchange between thermodynamic and economic aspects.

Thermodynamic analysis of a novel power-hydrogen cogeneration system

In recent decades, hydrogen is considered as a secondary clean energy source, commonly referred to as an energy carrier. Hydrogen can be used to move, store and deliver energy in a form that can be easily used along with many other applications. Due to the significant role of hydrogen, a novel combined system for cogeneration of power and hydrogen is proposed in this paper. The proposed system is integrated from a Gas Turbine-Modular Helium Reactor (GT-MHR) and a biogas steam reforming (BSR) system to produce power and hydrogen, simultaneously. Biogas mixture consists of a considerable amount of methane and carbon dioxide as well as negligible amounts of other gases. A comprehensive thermodynamic modeling (i.e., energy and exergy analysis) of the proposed combined system is carried out. It is found that the proposed combined GT-MHR/BSR system can produce hydrogen and net output power of 0.217 kg/s and 260.13 MW, respectively. In this case, the overall exergy destruction rate, energy efficiency, and exergy efficiency of the combined GT-MHR/BSR system are calculated 329.31 MW, 47.69%, and 51.08%, respectively, showing a considerable enhancement in the efficiency of the basic system (GT-MHR cycle) from first and second laws of thermodynamics viewpoints. Moreover, the results of exergy analysis indicated that among all components, reactor core is accountable for the highest exergy destruction through the system (57.64%). To better understand the effect of various parameters on the performance of system, a comprehensive parametric study of some key thermodynamic parameters on performance criteria is performed. It is concluded that a higher energy and exergy efficiencies can be obtained by increasing the turbine inlet temperature, steam to carbon molar ratio, and turbine pressure ratio or decreasing the carbon dioxide to methane molar ratio and compressor pressure ratio. Last but not the least, it is demonstrated that the performance of the proposed integrated system can be maximized based on the reformer temperature.

An exergoeconomic assessment of waste heat recovery from a Gas Turbine-Modular Helium Reactor using two transcritical CO2 cycles

A comprehensive study is performed on an energy conversion system which combines a gas turbine-modular helium reactor (GT-MHR) and two transcritical CO2 cycles (tCO2). The aim of this study is to assess the energy, exergy and economic behavior of the proposed system, considering five indicators: the energy efficiency, the exergy efficiency, the total exergy destruction cost rate, the overall exergoeconomic factor and the total cost rate. A parametric study is also conducted to evaluate the influence of key decision variables on the GT-MHR/tCO2 performance. Finally, the combined cycle is optimized to minimize the total cost rate. The results show that the energy efficiency of GT-MHR/tCO2 cycle is 7.92% higher than that of the simple GT-MHR cycle at 850°C. The largest exergy destruction rate takes place in the reactor, and after that in the helium turbine and the recuperator. The components in tCO2 cycles have less exergy destruction. When the optimization is conducted based on the exergoeconomics, the overall exergoeconomic factor, the total cost rate and the total exergy destruction cost rate are 55.2%, 20,752$/h and 9292$/h, respectively.

Exergoeconomic evaluation and optimization of a novel combined augmented Kalina cycle/gas turbine-modular helium reactor

A new combined system including Gas Turbine-Modular Helium Reactor (GT-MHR) and an augmented Kalina cycle (AKC) is proposed, analyzed and optimized thermodynamically and economically. The simulation is performed using the conservation of energy, exergy balance and cost equations for each system component. For comparison purposes the previously published data for the combined cycle consisting of the GT-MHR and a conventional Kalina cycle (GT-MHR/KCS34), are also presented. Parametric studies are carried out to show the influences on exergy efficiency and total product unit cost of such decision parameters as compressor pressure ratio, pump pressure ratio, ammonia concentrations at different state points and separator temperature. The results indicate that the maximum exergy efficiency of the proposed system is 8.7% and 0.64% higher compared to the corresponding values for the GT-MHR and GT-MHR/KCS34, respectively. The results also show that the minimum total product unit cost for GT-MHR/AKC is 11.3% and 2.53% lower than the corresponding values for the GT-MHR and GT-MHR/KCS34, respectively. It is observed that, under optimized condition, the helium mass flow rate in GT-MHR is reduced as the system is combined with the AKC. This is significant in reducing the size of system and consequently having more economically efficient system.

Analysis and Assessment of a Gas Turbine-Modular Helium Reactor for Nuclear Desalination

A thermodynamic analysis of the coupling of a reverse osmosis (RO) process with the gas turbine-modular helium reactor (GT-MHR) is presented in which the waste heat is utilized for the generation of steam as it is expanded in a steam turbine. A comprehensive parametric study is carried out to reveal the effect of some parameters such as compression ratio, turbine inlet temperature, recovery ratio, and preheated feed seawater inlet temperature on the exergy efficiencies of the RO process, electricity generation process, electricity generation without steam turbine work output, and overall system. The analysis shows that the exergy efficiency of the electric generation process is increased by 10.3%, if the waste heat from the reactor is utilized. The exergy efficiencies of the RO process, electricity generation process, electricity generation without steam turbine work output, and overall system are found to be 89.0%, 40.0%, 29.7%, and 41.0%, respectively.

Computational fluid dynamics analysis of the initial stages of a VHTR air-ingress accident using a scaled-down model

An air-ingress accident is considered to be one of the design basis accidents of a very high-temperature gas-cooled reactor (VHTR). The air-ingress accident is initiated, in its worst-case scenario, by a complete break of the hot duct in what is referred to as a double-ended guillotine break. This leads to an initial loss of the primary helium coolant via depressurization. Following the depressurization process, the air–helium mixture in the reactor cavity could enter the reactor core via the hot duct and hot exit plenum. In the event that air ingresses into the reactor vessel, the high-temperature graphite structures in the reactor core and hot plenum will chemically react with the air, which could lead to damage of in-core graphite structures and fuel, release of carbon monoxide and carbon dioxide, core heat up, failure of the structural integrity of the system, and eventually the release of radionuclides to the environment.Studies in the available literature focus on the phenomena of the air ingress accident that occur after the termination of the depressurization, such as density-driven stratified flow, molecular diffusion, and natural circulation. However, a recent study shows that flow reversal could occur due to Taylor wave expansion near the end of the depressurization, which could affect subsequent stages of the air ingress accident scenario. Therefore, to properly understand and evaluate the depressurization effects, numerical simulations are performed for the double-ended guillotine break of the Gas Turbine-Modular Helium Reactor (GT-MHR) cross vessel with a computational fluid dynamics (CFD) tool, ANSYS FLUENT.A benchmark and error quantification study of the depressurization shows that the ANSYS FLUENT model can predict the depressurization problem with relatively low uncertainty. In addition, the computational results show that the depressurization of a double-ended guillotine break behaves as an isentropic process. The observed flow oscillations near the end of the depressurization promote mixing of helium gas and air near the break. The results of the CFD analyses also show that the density-driven stratified flow, which is postulated to be the next stage of the air-ingress accident scenario, is strongly dependent on the density difference between the air–helium mixture in the containment and the helium in the reactor vessel. Therefore, the flow oscillations near the end of the depressurization stage may have a minor, yet notable, effect to slow down the air ingress due to density-driven stratified flow by decreasing the bulk density of the gas mixture in the containment through the addition of helium and increasing the bulk density in the reactor vessel through the addition of air.

Investigation of a gas turbine-modular helium reactor using reactor grade plutonium with 232Th and 238U

Utilization of natural uranium (nat-U) and thorium as fertile fuels has been investigated by in a Gas Turbine – Modular Helium Reactor (GTMHR) using reactor grade plutonium as driver fuel. A neutronic analysis for the full core reactor was performed by using MCNP5 with ENDF/B-VI cross-section library. Different mixture ratios were tested in order to find the appropriate mixture ratio of fertile and fissile fuel particles that gives a comparable keff value of the reference uranium fuel. Time dependent calculations were performed by using MONTEBURN2.0 with ORIGEN2.2 for each selected mixture. Different parameters (operation time, burnup value, fissile isotope change, etc.) were subject of performance comparison. The operation time and burnup values were close to each other with nat-U and thorium, namely 3205 days and 176 GWd/MTU for the former and 3175 days 181 GWd/MTU for the latter fertile fuel. In addition, the fissile isotope amount changed from initially 6940.1 kg–4579.2 kg at the end of its operation time for nat-U. These values were obtained for thorium as 6603.3 kg–4250.2 kg, respectively.

Exergoeconomic analysis with reliability and availability considerations of a nuclear energy-based combined cycle power plant

The reliability and availability considerations are introduced in the exergoeconomic investigation of a combined cycle power plant in which an organic Rankine cycle is employed to recover the waste heat from a GT-MHR (Gas Turbine Modular Helium Reactor) power plant. The SPECO (specific exergy costing) theory is employed to investigate the exergoeconomic performance of the system and assess the specific cost of the output power. For the reliability analysis, however, the SSM (state-space method) along with the probabilistic analysis of Markov processes is employed. After conducting a parametric analysis, the performance of the cycle is optimized with respect to the specific cost of output power, with and without reliability considerations. The effects of the system failure and repair rates are examined on the cost of power and availability of the combined cycle by the sensitivity analysis. The optimization results show that, the specific cost of output power for the combined cycle is around 12% lower than that for the stand alone GT-MHR. However, availability of the combined cycle is lower than that of the GT-MHR as the former has more components and a complicated system.

Weapons Grade Plutonium utilization with fertile materials in a Gas Turbine-Modular Helium Reactor

In this study, neutronic performances of the fertile thorium and natural uranium were studied in a Gas Turbine-Modular Helium Reactor using Weapons Grade Plutonium as fissile fuel. In the first step of the calculation procedure, a series of neutronic calculations were made in order to find the proper mixture ratios for these fertile fuel mixtures by using MCNP5 with ENDF/B-VI cross-section library. After the determination of these mixture ratios, in order to compare these fuel mixtures, time dependent neutronic calculations were made by using Monteburns 2.0 with MCNP5 and Origen 2.2. According to the results obtained, different parameters (operation time, burnup value, fissile isotope production, etc.) were compared. Results of the first step showed that, in order to reach the reference keff value, 690.6kg more fissile isotope was used in natural uranium mixture than the thorium mixture. In the second step of this study, time dependent calculations showed that for the natural uranium mixture, operation time and burnup values were found as 1935days and 177.76GWd/MTU, respectively, while these values for thorium mixture were 1925days and 153.95GWd/MTU.

Life-cycle impacts from novel thorium–uranium-fuelled nuclear energy systems

Electricity generated from nuclear power plants is generally associated with low emissions per kWh generated, an aspect that feeds into the wider debate surrounding nuclear power. This paper seeks to investigate how life-cycle emissions would be affected by including thorium in the nuclear fuel cycle, and in particular its inclusion in technologies that could prospectively operate open Th–U-based nuclear fuel cycles. Three potential Th–U-based systems operating with open nuclear fuel cycles are considered: AREVA’s European Pressurised Reactor; India’s Advanced Heavy Water Reactor; and General Atomics’ Gas-Turbine Modular Helium Reactor. These technologies are compared to a reference U-fuelled European Pressurised Reactor. A life-cycle analysis is performed that considers the construction, operation, and decommissioning of each of the reactor technologies and all of the other associated facilities in the open nuclear fuel cycle. This includes the development of life-cycle analysis models to describe the extraction of thorium from monazitic beach sands and for the production of heavy water. The results of the life-cycle impact analysis highlight that the reference U-fuelled system has the lowest overall emissions per kWh generated, predominantly due to having the second-lowest uranium ore requirement per kWh generated. The results highlight that the requirement for mined or recovered uranium (and thorium) ore is the greatest overall contributor to emissions, with the possible exception of nuclear energy systems that require heavy water. In terms of like-for-like comparison of mining and recovery techniques, thorium from monazitic beach sands has lower overall emissions than uranium that is either conventionally mined or recovered from in-situ leaching. Although monazitic beach sands (and equivalent placer deposits) only form 30% of the overall known thorium ore deposits, it is expected that such deposits would generally be utilised first if thorium becomes a viable nuclear fuel. Overall, for these four nuclear energy technologies, the range of CO2(eq) emissions per kWh generated (6.60–13.2 gCO2(eq)/kWh) appears to be low in comparison to the majority of electricity-generating technologies.

A thermodynamic comparison between organic Rankine and Kalina cycles for waste heat recovery from the Gas Turbine-Modular Helium Reactor

A comparative thermodynamic analysis and optimization is presented for waste heat recovery from the Gas Turbine-Modular Helium Reactor (GT-MHR) employing organic Rankine cycle (ORC) and Kalina cycle (KC). Thermodynamic models are developed for the stand alone GT-MHR and the two proposed combined cycles and the effects on the performances of the cycles are investigated of decision variables. The cycles' performances are then optimized based on the first and second law of thermodynamics. The results showed that, employing ORC is more appropriate than KC for GT-MHR waste heat recovery. The first and second law efficiencies of the combined GT-MHR/ORC are higher than those of the combined GT-MHR/KC. In addition, the helium mass flow rate in the combined GT-MHR/ORC is significantly lower than that in the combined GT-MHR/KC. Moreover, the high-pressure level of the ORC is extremely lower than that of the KC under optimized conditions. Furthermore, the superheated vapor at the ORC turbine exit avoids droplet erosion and allows for reliable operation while the stream exiting the KC turbine is a two-phase flow.

On the exergoeconomic assessment of employing Kalina cycle for GT-MHR waste heat utilization

Exergoeconomic concept is applied to compare the performance of the Gas Turbine-Modular Helium Reactor (GT-MHR) plant with a proposed combined GT-MHR/Kalina cycle in which the waste heat from the GT-MHR is recovered by the Kalina cycle for power generation. Thermodynamic and exergoeconomic models are developed to investigate the cycles’ performance and assess the unit cost of the products. A sensitivity analysis is performed prior to the optimization of the cycles’ performances from the view points of thermodynamics and economics. The results indicate that, when the performances of the two cycles are optimized economically, the efficiency and total product unit cost of the combined cycle is 8.2% higher and 8.8% lower than the corresponding values for the GT-MHR. It is interesting to note that, under these conditions, the total investment cost rate for the combined cycle is just slightly higher than that of the stand alone GT-MHR.

A Comparative Exergoeconomic Analysis of Waste Heat Recovery from a Gas Turbine-Modular Helium Reactor via Organic Rankine Cycles

A comparative exergoeconomic analysis is reported for waste heat recovery from a gas turbine-modular helium reactor (GT-MHR) using various configurations of organic Rankine cycles (ORCs) for generating electricity. The ORC configurations studied are: a simple organic Rankine cycle (SORC), an ORC with an internal heat exchanger (HORC) and a regenerative organic Rankine cycle (RORC). Exergoeconomic analyses are performed with the specific exergy costing (SPECO) method. First, energy and exergy analyses are applied to the combined cycles. Then, a cost-balance, as well as auxiliary equations are developed for the components to determine the exergoeconomic parameters for the combined cycles and their components. The three combined cycles are compared considering the same operating conditions for the GT-MHR cycle, and a parametric study is done to reveal the effects on the exergoeconomic performance of the combined cycles of various significant parameters, e.g., turbine inlet and evaporator temperatures and compressor pressure ratio. The results show that the GT-MHR/RORC has the lowest unit cost of electricity generated by the ORC turbine. This value is highest for the GT-MHR/HORC. Furthermore, the GT-MHR/RORC has the highest and the GT-MHR/HORC has the lowest exergy destruction cost rate.

Exergoeconomic assessment and parametric study of a Gas Turbine-Modular Helium Reactor combined with two Organic Rankine Cycles

An exergoeconomic analysis is reported for a combined system with a net electrical output of 299 MW in which waste heat from a Gas Turbine-Modular Helium Reactor (GT-MHR) is utilized by two Organic Rankine Cycles (ORCs). A parametric study is also done to reveal the effects on the exergoeconomic performance of the combined system of such significant parameters as compressor pressure ratio, turbine inlet temperature, temperatures of evaporators, pinch point temperature difference in the evaporators and degree of superheat at the ORC (Organic Rankine Cycle) turbines inlet. Finally the combined cycle performance is optimized from the viewpoint of exergoeconomics. The results show that the precooler, the intercooler and the ORC condensers exhibit the worst exergoeconomic performance. For the overall system, the exergoeconomic factor, the capital cost rate and the exergy destruction cost rate are determined to be 37.95%, 6876 $/h and 11,242 $/h, respectively. Also, it is observed that the unit cost of electricity produced by the GT-MHR turbine increases with increasing GT-MHR turbine inlet temperature but decreases as the other above mentioned parameters increase.