{"id":{"repo_id":"gatech","oai_identifier":"oai:repository.gatech.edu:1853/81529"},"canonical_url":"https://search.dev.ndltd.org/etd/gatech/oai:repository.gatech.edu:1853/81529","repository":{"repo_id":"gatech","name":"Georgia Tech","base_url":"https://repository.gatech.edu/server/oai/request"},"display":{"title":"LEU+ Fuel Cycle Investigation of the BWRX-300 Design Using Neutronic and Two-Phase Thermal Hydraulic Analyses","abstract":"Of the many advanced reactor concepts proposed, small modular reactors (SMRs) are of particular interest due to their relatively low upfront capital cost, scalability, and enhanced safety features. Of SMR concepts, General Electric Hitachi Nuclear Energy’s (GEH) BWRX-300 design is one of the most promising, with several countries strongly considering its viability. The BWRX-300 is a 300 MWe boiling water reactor (BWR) utilizing a typical direct cycle balance of plant (BOP); this reactor concept greatly reduces the complexity of earlier BWRs, has robust passive safety systems, and has vast operational experience due to the prevalence of BWR type reactors across the world. Part of this reduction of complexity of the BWRX-300 is the use of natural circulation rather than the forced circulation employed by the previous generation of BWRs. This does, however, also remove the ability to extend the cycle by increasing mass flow rate at the end of the cycle, a practice utilized by previous and current BWR fleets. Removing such a means of control of the fuel cycle may prove disadvantageous for the fuel cycle performance. Recent trends specifically applied for pressurized water reactors (PWRs) focus on utilizing low enriched uranium plus (LEU+) fuel to further improve the cycle length and subsequent economics of the current fleet of reactors and other PWR concepts ([1], [2]). These considerations and trends justify the need for current research on adopting LEU+ for the BWRX-300 design and the subsequent economic impact. To analyze the economics behind this adoption, many different tools and methods must be utilized. Monte Carlo (MC) and computational fluid dynamics (CFD) codes are considered to have the highest accuracies of modeling tools available to represent neutronic and thermal hydraulic conditions respectively. When performing coupled calculations between these two codes, large computational cost is seen, especially in neutronic burnup calculations in three dimensions. The main challenge when performing coupled neutronic burnup calculations in BWRs is the accurate capture of the thermal fields, which can greatly change the results of subsequent neutronic calculations. In areas of the core where boiling occurs, the density of the coolant decreases, leading to lower moderation and different depletion results. This work investigates the implementation of a loose coupling scheme and the subsequent analysis of the neutronic results to achieve more economical cycle length calculations via LEU+ fuel. In this case, representative thermal hydraulic (TH) fields are generated via a manual coupling sequence with MC neutronic analysis on the typical low enriched uranium (LEU) fuel cycle. TH results obtained from this manual coupling sequence are then utilized as input parameters for LEU and LEU+ MC burnup calculations, in which the results will be used with a non-linear reactivity model (NLRM) to perform analysis and sensitivity studies on the economics of the fuel cycle. The goal of this methodology is to utilize a simplified manner to obtain coupled results for highly heterogeneous, time dependent systems without the need for complicated and computationally expensive tightly coupled analysis. The results obtained from this work show good agreement between generated TH fields from the reduced order solver further developed as part of this work and licensed industry TH codes; burnup calculations and subsequent economic analysis on the overall fuel cycle shows a net benefit of increasing enrichment when compared to a benchmark case using LEU fuel enrichment, reducing total costs of operation by up to 11.29% when considering the costs of fuel and outages.","abstract_html":"Of the many advanced reactor concepts proposed, small modular reactors (SMRs) are of particular interest due to their relatively low upfront capital cost, scalability, and enhanced safety features. Of SMR concepts, General Electric Hitachi Nuclear Energy’s (GEH) BWRX-300 design is one of the most promising, with several countries strongly considering its viability. The BWRX-300 is a 300 MWe boiling water reactor (BWR) utilizing a typical direct cycle balance of plant (BOP); this reactor concept greatly reduces the complexity of earlier BWRs, has robust passive safety systems, and has vast operational experience due to the prevalence of BWR type reactors across the world. Part of this reduction of complexity of the BWRX-300 is the use of natural circulation rather than the forced circulation employed by the previous generation of BWRs. This does, however, also remove the ability to extend the cycle by increasing mass flow rate at the end of the cycle, a practice utilized by previous and current BWR fleets. Removing such a means of control of the fuel cycle may prove disadvantageous for the fuel cycle performance. Recent trends specifically applied for pressurized water reactors (PWRs) focus on utilizing low enriched uranium plus (LEU+) fuel to further improve the cycle length and subsequent economics of the current fleet of reactors and other PWR concepts ([1], [2]). These considerations and trends justify the need for current research on adopting LEU+ for the BWRX-300 design and the subsequent economic impact. To analyze the economics behind this adoption, many different tools and methods must be utilized. Monte Carlo (MC) and computational fluid dynamics (CFD) codes are considered to have the highest accuracies of modeling tools available to represent neutronic and thermal hydraulic conditions respectively. When performing coupled calculations between these two codes, large computational cost is seen, especially in neutronic burnup calculations in three dimensions. The main challenge when performing coupled neutronic burnup calculations in BWRs is the accurate capture of the thermal fields, which can greatly change the results of subsequent neutronic calculations. In areas of the core where boiling occurs, the density of the coolant decreases, leading to lower moderation and different depletion results. This work investigates the implementation of a loose coupling scheme and the subsequent analysis of the neutronic results to achieve more economical cycle length calculations via LEU+ fuel. In this case, representative thermal hydraulic (TH) fields are generated via a manual coupling sequence with MC neutronic analysis on the typical low enriched uranium (LEU) fuel cycle. TH results obtained from this manual coupling sequence are then utilized as input parameters for LEU and LEU+ MC burnup calculations, in which the results will be used with a non-linear reactivity model (NLRM) to perform analysis and sensitivity studies on the economics of the fuel cycle. The goal of this methodology is to utilize a simplified manner to obtain coupled results for highly heterogeneous, time dependent systems without the need for complicated and computationally expensive tightly coupled analysis. The results obtained from this work show good agreement between generated TH fields from the reduced order solver further developed as part of this work and licensed industry TH codes; burnup calculations and subsequent economic analysis on the overall fuel cycle shows a net benefit of increasing enrichment when compared to a benchmark case using LEU fuel enrichment, reducing total costs of operation by up to 11.29% when considering the costs of fuel and outages.","abstract_has_math":false,"creators":["Monaghan, John Annas"],"institution":"Georgia Institute of Technology","degree_name":null,"degree_level":"Masters","degree_discipline":null,"degree_department":"Mechanical Engineering","school":null,"contributors":[],"advisors":["Kotlyar, Dan"],"committee_chairs":[],"committee_members":["Ghiaasiaan, S.","Petrovic, Bojan"],"year":2025,"date_issued":"2025-04-23","date_published":"2025-04-23","updated_at":"2026-07-27T19:49:34Z","subjects":["Fuel Cycle","Neutronic Analysis","Thermal Hydraulic Analysis","Coupled Analysis","LEU+"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/1853/81529","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Kotlyar, Dan"]},{"key":"dc:contributor.committeemember","label":"Committee Member","values":["Ghiaasiaan, S.","Petrovic, Bojan"]},{"key":"dc:contributor.department","label":"Department","values":["Mechanical Engineering"]},{"key":"dc:creator","label":"Author","values":["Monaghan, John Annas"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-05-21T20:40:53Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-05-21T20:40:53Z"]},{"key":"dc:date.issued","label":"Date","values":["2025-04-23"]},{"key":"dc:publisher","label":"Institution","values":["Georgia Institute of Technology"]},{"key":"dc:type","label":"Dc Type","values":["Text"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Masters"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Fuel Cycle","Neutronic Analysis","Thermal Hydraulic Analysis","Coupled Analysis","LEU+"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://hdl.handle.net/1853/81529"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Of the many advanced reactor concepts proposed, small modular reactors (SMRs) are of particular interest due to their relatively low upfront capital cost, scalability, and enhanced safety features. Of SMR concepts, General Electric Hitachi Nuclear Energy’s (GEH) BWRX-300 design is one of the most promising, with several countries strongly considering its viability. The BWRX-300 is a 300 MWe boiling water reactor (BWR) utilizing a typical direct cycle balance of plant (BOP); this reactor concept greatly reduces the complexity of earlier BWRs, has robust passive safety systems, and has vast operational experience due to the prevalence of BWR type reactors across the world. Part of this reduction of complexity of the BWRX-300 is the use of natural circulation rather than the forced circulation employed by the previous generation of BWRs. This does, however, also remove the ability to extend the cycle by increasing mass flow rate at the end of the cycle, a practice utilized by previous and current BWR fleets. Removing such a means of control of the fuel cycle may prove disadvantageous for the fuel cycle performance. Recent trends specifically applied for pressurized water reactors (PWRs) focus on utilizing low enriched uranium plus (LEU+) fuel to further improve the cycle length and subsequent economics of the current fleet of reactors and other PWR concepts ([1], [2]). These considerations and trends justify the need for current research on adopting LEU+ for the BWRX-300 design and the subsequent economic impact. To analyze the economics behind this adoption, many different tools and methods must be utilized. Monte Carlo (MC) and computational fluid dynamics (CFD) codes are considered to have the highest accuracies of modeling tools available to represent neutronic and thermal hydraulic conditions respectively. When performing coupled calculations between these two codes, large computational cost is seen, especially in neutronic burnup calculations in three dimensions. The main challenge when performing coupled neutronic burnup calculations in BWRs is the accurate capture of the thermal fields, which can greatly change the results of subsequent neutronic calculations. In areas of the core where boiling occurs, the density of the coolant decreases, leading to lower moderation and different depletion results. This work investigates the implementation of a loose coupling scheme and the subsequent analysis of the neutronic results to achieve more economical cycle length calculations via LEU+ fuel. In this case, representative thermal hydraulic (TH) fields are generated via a manual coupling sequence with MC neutronic analysis on the typical low enriched uranium (LEU) fuel cycle. TH results obtained from this manual coupling sequence are then utilized as input parameters for LEU and LEU+ MC burnup calculations, in which the results will be used with a non-linear reactivity model (NLRM) to perform analysis and sensitivity studies on the economics of the fuel cycle. The goal of this methodology is to utilize a simplified manner to obtain coupled results for highly heterogeneous, time dependent systems without the need for complicated and computationally expensive tightly coupled analysis. The results obtained from this work show good agreement between generated TH fields from the reduced order solver further developed as part of this work and licensed industry TH codes; burnup calculations and subsequent economic analysis on the overall fuel cycle shows a net benefit of increasing enrichment when compared to a benchmark case using LEU fuel enrichment, reducing total costs of operation by up to 11.29% when considering the costs of fuel and outages."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["M.S."]},{"key":"dc:format.mimetype","label":"Dc Format Mimetype","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["LEU+ Fuel Cycle Investigation of the BWRX-300 Design Using Neutronic and Two-Phase Thermal Hydraulic Analyses"]}]}],"canonical_facts":{"dc:contributor.advisor":["Kotlyar, Dan"],"dc:contributor.committeemember":["Ghiaasiaan, S.","Petrovic, Bojan"],"dc:contributor.department":["Mechanical Engineering"],"dc:creator":["Monaghan, John Annas"],"dc:date.accessioned":["2026-05-21T20:40:53Z"],"dc:date.available":["2026-05-21T20:40:53Z"],"dc:date.issued":["2025-04-23"],"dc:description.abstract":["Of the many advanced reactor concepts proposed, small modular reactors (SMRs) are of particular interest due to their relatively low upfront capital cost, scalability, and enhanced safety features. Of SMR concepts, General Electric Hitachi Nuclear Energy’s (GEH) BWRX-300 design is one of the most promising, with several countries strongly considering its viability. The BWRX-300 is a 300 MWe boiling water reactor (BWR) utilizing a typical direct cycle balance of plant (BOP); this reactor concept greatly reduces the complexity of earlier BWRs, has robust passive safety systems, and has vast operational experience due to the prevalence of BWR type reactors across the world. Part of this reduction of complexity of the BWRX-300 is the use of natural circulation rather than the forced circulation employed by the previous generation of BWRs. This does, however, also remove the ability to extend the cycle by increasing mass flow rate at the end of the cycle, a practice utilized by previous and current BWR fleets. Removing such a means of control of the fuel cycle may prove disadvantageous for the fuel cycle performance. Recent trends specifically applied for pressurized water reactors (PWRs) focus on utilizing low enriched uranium plus (LEU+) fuel to further improve the cycle length and subsequent economics of the current fleet of reactors and other PWR concepts ([1], [2]). These considerations and trends justify the need for current research on adopting LEU+ for the BWRX-300 design and the subsequent economic impact. To analyze the economics behind this adoption, many different tools and methods must be utilized. Monte Carlo (MC) and computational fluid dynamics (CFD) codes are considered to have the highest accuracies of modeling tools available to represent neutronic and thermal hydraulic conditions respectively. When performing coupled calculations between these two codes, large computational cost is seen, especially in neutronic burnup calculations in three dimensions. The main challenge when performing coupled neutronic burnup calculations in BWRs is the accurate capture of the thermal fields, which can greatly change the results of subsequent neutronic calculations. In areas of the core where boiling occurs, the density of the coolant decreases, leading to lower moderation and different depletion results. This work investigates the implementation of a loose coupling scheme and the subsequent analysis of the neutronic results to achieve more economical cycle length calculations via LEU+ fuel. In this case, representative thermal hydraulic (TH) fields are generated via a manual coupling sequence with MC neutronic analysis on the typical low enriched uranium (LEU) fuel cycle. TH results obtained from this manual coupling sequence are then utilized as input parameters for LEU and LEU+ MC burnup calculations, in which the results will be used with a non-linear reactivity model (NLRM) to perform analysis and sensitivity studies on the economics of the fuel cycle. The goal of this methodology is to utilize a simplified manner to obtain coupled results for highly heterogeneous, time dependent systems without the need for complicated and computationally expensive tightly coupled analysis. The results obtained from this work show good agreement between generated TH fields from the reduced order solver further developed as part of this work and licensed industry TH codes; burnup calculations and subsequent economic analysis on the overall fuel cycle shows a net benefit of increasing enrichment when compared to a benchmark case using LEU fuel enrichment, reducing total costs of operation by up to 11.29% when considering the costs of fuel and outages."],"dc:description.degree":["M.S."],"dc:format.mimetype":["application/pdf"],"dc:identifier.uri":["https://hdl.handle.net/1853/81529"],"dc:publisher":["Georgia Institute of Technology"],"dc:subject":["Fuel Cycle","Neutronic Analysis","Thermal Hydraulic Analysis","Coupled Analysis","LEU+"],"dc:title":["LEU+ Fuel Cycle Investigation of the BWRX-300 Design Using Neutronic and Two-Phase Thermal Hydraulic Analyses"],"dc:type":["Text"],"thesis:degree_level":["Masters"]},"updated_at":"2026-07-27T19:49:34Z"}