Nuclear reactor systems present a promising sustainable energy source for the future. Simply, a nuclear reactor heats a coolant that powers a turbine to create electricity. The coolant then can either be re-cooled or can be used for process heat applications. By utilizing the heat off the reactor less energy is wasted. A few of the proposed uses of the wasted heat are water desalination, hydrogen production, or pyrolysis. Nuclear power plants most often provide baseload power and are very inflexible. One way to address this is to use nuclear hybrid energy systems. The goal of this research is to create a system that mimics the waste heat from a reactor, demonstrates how to utilize that heat, and shows that when energy demand is low the reactor does not need to reduce power; the energy can be directed elsewhere to create goods. We have developed an Energy Conversion Loop to act as a testbed for experimentation of the aforementioned processes and test the possibility of nuclear hybrid energy systems. The current design consists of a series of heat exchangers that transfer heat between hot air 427 °C (800 °F) and room temperature water. Each loop of the system mimics a type of process that can be tested with a waste heat application. Early models show the system is capable of producing air temperatures near 427 °C (800 °F) and steam temperatures of 154.4 °C (310 °F). These temperatures match needed process heat temperatures for pyrolysis, multi-effect distillation, and multi-stage flash distillation and can be used to simulate other processes for lab scale testing of wasted process heat. Physical testing will be completed in the future to confirm these results.

Results of a system evaluation and lifecycle cost analysis are presented for a commercial-scale high-temperature electrolysis (HTE) central hydrogen production plant. The plant design relies on grid electricity to power the electrolysis process and system components, and industrial natural gas to provide process heat. The HYSYS process analysis software was used to evaluate the reference central plant design capable of producing 50,000 kg/day of hydrogen. The HYSYS software performs mass and energy balances across all components to allow optimized of the design using a detailed process flow sheet and realistic operating conditions specified the analyst. The lifecycle cost analysis was performed using the H2A analysis methodology developed by the Department of Energy (DOE) Hydrogen Program. This methodology utilizes Microsoft Excel spreadsheet analysis tools that require detailed plant performance information (obtained from HYSYS), along with financial and cost information to calculate lifecycle costs. The results of the lifecycle analyses indicate that for a 10% internal rate of return, a large central commercial-scale hydrogen production plant can produce 50,000 kg/day of hydrogen at an average cost of $2.68/kg. When the cost of carbon sequestration is taken into account, the average cost of hydrogen production increases by $0.40/kg to $3.08/kg.

A high temperature gas reactor, HTGR, can produce industrial process steam, high-temperature heat-transfer gases, and/or electricity. In conventional industrial processes, these products are generated by the combustion of fossil fuels such as coal and natural gas, resulting in significant emissions of greenhouse gases such as carbon dioxide. Heat or electricity produced in an HTGR could be used to supply process heat or electricity to conventional processes without generating any greenhouse gases. Process heat from a reactor needs to be transported by a gas to the industrial process. Two such gases were considered in this study: helium and steam. For this analysis, it was assumed that steam was delivered at 17 MPa and 540°C and helium was delivered at 7 MPa and at a variety of temperatures. The temperature of the gas returning from the industrial process and going to the HTGR must be within certain temperature ranges to maintain the correct reactor inlet temperature for a particular reactor outlet temperature. The returning gas may be below the reactor inlet temperature, ROT, but not above. The optimal return temperature produces the maximum process heat gas flow rate. For steam, the delivered pressure sets an optimal reactor outlet temperature based on the condensation temperature of the steam. ROTs greater than 769.7°C produce no additional advantage for the production of steam.

Results of analyses performed using the UniSim process analyses software to evaluate the performance of both a direct and indirect supercritical CO 2 Brayton power plant cycle with recompression at different reactor outlet temperatures are presented. The direct supercritical CO 2 power plant cycle transferred heat directly from a 600 MW t reactor to the supercritical CO 2 working fluid supplied to the turbine generator at approximately 20 MPa. The indirect supercritical CO 2 cycle assumed a helium-cooled Very High Temperature Reactor (VHTR), operating at a primary system pressure of approximately 7.0 MPa, delivered heat through an intermediate heat exchanger to the secondary indirect supercritical CO 2 recompression Brayton cycle, again operating at a pressure of about 20 MPa. For both the direct and indirect power plant cycles, sensitivity calculations were performed for reactor outlet temperature between 550°C and 850°C. The UniSim models used realistic component parameters and operating conditions to model the complete reactor and power conversion systems. CO 2 properties were evaluated, and the operating ranges of the cycles were adjusted to take advantage of the rapidly changing properties of CO 2 near the critical point. The results of the analyses showed that, for the direct supercritical CO 2 power plant cycle, thermal efficiencies in the range of approximately 40 to 50% can be achieved over the reactor coolant outlet temperature range of 550°C to 850°C. For the indirect supercritical CO 2 power plant cycle, thermal efficiencies were approximately 11–13% lower than those obtained for the direct cycle over the same reactor outlet temperature range.

NASA has been evaluating closed-loop atmosphere revitalization architectures that include carbon dioxide (CO 2 ) reduction technologies. The CO 2 and steam (H 2 O) co-electrolysis process is one of the reduction options that NASA has investigated. Utilizing recent advances in the fuel cell technology sector, the Idaho National Laboratory, INL, has developed a CO 2 and H 2 O co-electrolysis process to produce oxygen and syngas (carbon monoxide (CO) and hydrogen (H 2 ) mixture) for terrestrial (energy production) application. The technology is a combined process that involves steam electrolysis, CO 2 electrolysis, and the reverse water gas shift (RWGS) reaction. Two process models were developed to evaluate novel approaches for energy storage and resource recovery in a life support system. In the first model, products from the INL co-electrolysis process are combined to produce methanol fuel. In the second co-electrolysis, products are separated with a pressure swing adsorption (PSA) process. In both models the fuels are burned with added oxygen to produce H 2 O and CO 2 , the original reactants. For both processes, the overall power increases as the syngas ratio, H 2 /CO, increases because more water is needed to produce more hydrogen at a set CO 2 incoming flow rate. The power for the methanol cases is less than pressure swing adsorption, PSA, because heat is available from the methanol reactor to preheat the water and carbon dioxide entering the co-electrolysis process.

High temperature electrolysis (HTE) involves the splitting of steam into hydrogen and oxygen at high temperatures. The primary advantage of HTE over conventional low temperature electrolysis is that considerably higher hydrogen production efficiencies can be achieved. Performing the electrolysis process at high temperatures results in more favorable thermodynamics for electrolysis, more efficient production of electricity, and allows direct use of process heat to generate steam. This paper presents the results of process analyses performed to evaluate the hydrogen production efficiencies of an HTE plant coupled to a 600 MWt Modular Helium Reactor (MHR) that supplies both the electricity and process heat needed to drive the process. The MHR operates with a coolant outlet temperature of 950 C. Approximately 87% of the high-temperature heat is used to generate electricity at high efficiency using a direct, Brayton-cycle power conversion system. The remaining high-temperature heat is used to generate a superheated steam / hydrogen mixture that is supplied to the electrolyzers. The analyses were performed using the HYSYS process modeling software. The model used to perform the analyses consisted of three loops; a primary high temperature helium loop, a secondary helium loop and the HTE process loop. The detailed model included realistic representations of all major components in the system, including pumps, compressors, heat exchange equipment, and the electrolysis stack. The design of the hydrogen production process loop also included a steam-sweep gas system to remove oxygen from the electrolysis stack so that it can be recovered and used for other applications. Results of the process analyses showed that hydrogen production efficiencies in the range of 45% to 50% are achievable with this system.