Year: 2025
Type: report
Abstract: This report looks at the viability and best approach when producing synthetic fuels using heat and power supplied by advanced nuclear energy systems. The report looks at a low temperature integration pathway with four types of advanced reactors: a pressurized water reactor (PWR), an advanced light water reactor (A-LWR), a sodium fast reactor (SFR), and a high-temperature gas-cooled reactor (HTGR). A failure modes and effects analysis (FMEA) of the coupling system between the nuclear plant and the synthetic fuel systems is performed with the goal of identifying the reliability of such a thermal delivery system. Furthermore, a high temperature pathway is investigated for synfuel coupling to determine if this is more efficient and more cost effective as a coupling approach. The two key feedstocks used in the synfuels production process are hydrogen (H2) and carbon dioxide (CO2). High-temperature steam electrolysis (HTSE) allows the efficient production of the H2 feedstock while the CO2 for this process is obtained from solid-sorbent direct air capture (DAC). Both processes utilize electricity and heat (steam) that can be sourced from advanced reactor systems. Obtaining H2 using HTSE was found to use 18.5 MWe of electricity and 3.8 MWth of heat to produce 0.5 t/hour of H2. Likewise, DAC required 4.6 MWe and 6.6 MWth to produce 3.1 t/hour of CO2. With these supply rates of feedstock, the synfuel system produces 11.9 MWth of fuel. The synthetic fuel process requires 0.96 MWe of electricity but, due to its exothermic reactions, produces 3.8 MWth of heat, which then can be used to provide the HTSE steam requirements without requiring steam from the nuclear system. To supply heat to the DAC process, steam is extracted from the nuclear plant steam turbines. The report provides comprehensive diagrams for each reactor power conversion cycle in consideration and the piping and instrumentation diagrams for the optimized thermal delivery system to the DAC process. For each design, the maximum synfuel production rate is calculated assuming all power and steam from the reactor was provided to the DAC, HTSE, and synfuel system. The SFR was found to give the highest synfuel efficiency with 19.3% of the reactors’ thermal power converted to chemical energy within the product diesel. The HTGR obtained a similar efficiency, reaching 18.8% synfuel production efficiency. The lower electrical efficiencies of the light water reactor (LWR) designs led to synfuel efficiencies of 16.4% for the pressurized water reactor (PWR) and 14.2% for the A-LWR. An FMEA was conducted on the thermal delivery system that supplied heat from the turbine to the DAC plant. Generic failure modes for components were evaluated along with specific failure probabilities taken from literature for each component within the thermal delivery system. Component failure modes were considered arising from load conditions, applied temperatures, external environmental conditions, and wear. Using the failure probabilities from literature, a risk priority number (RPN) was assigned to each component’s most high-risk failure mode. Based on a 30-year operational duration and reactor-specific system demands, it was found that shell-and-tube (S&T) heat exchangers, plate-and-frame (P&F) heat exchangers, the steam drum, and turbine components yielded high RPN values while flow, level, and temperature sensors generally had low RPN values. Aside from the RPN results, a few pump and turbine component failure probabilities were calculated to be higher than 0.5, which significantly impacts the heat extraction design system reliability. Using FMEA diagrams, heat extraction designs were identified as N+0 redundant series-reliability systems and will require future modifications to meet synthetic fuel plant reliability standards of over 99% reliability with no downtime. It was recommended to increase redundancy for highly RPN-ranked components and failure modes containing failure probabilities over 0.002. This report also describes the integration of high-temperature nuclear heat with synthetic fuel production using natural gas reforming. Different coupling options are considered for heat integration, and potential heat delivery fluid loops are evaluated. The requirements of the heat exchange system are provided to document the challenges with high temperature delivery systems. For the heat delivery loop, molten salts are found to outperform gases, but molten salt’s high freezing point requires a high return temperature that affects system efficiency. A significantly higher synfuel production efficiency of 55% is achieved using the high-temperature pathway compared to 19% for the low-temperature pathway. The higher efficiency of the high-temperature pathway translates into a much lower levelized cost of fuel (LCOF) of $66/MWh versus $675/MWh for the low-temperature pathway.
DOI: 10.2172/3399436
Institution: Idaho National Laboratory
Language: English
Subfield: Aerospace Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W7172399541