{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/132595"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/132595","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Investigation of MELCOR and STAR-CCM+ modeling capabilities to accurately predict air ingress rates from small breaks in high temperature gas-cooled reactors","abstract":"In a High Temperature Gas-cooled Reactor (HTGR), the study of postulated accident scenarios is necessary for licensing, deployment, and public perception. One specific scenario of concern is the air ingress following a primary loop break. Recent research has determined that small breaks are more likely than large double-ended guillotine breaks. The primary driving mechanism for the air ingress is the buoyant force due to the density differences of helium and air. This leads to a stratified flow through the break, with the lighter helium flowing above the heavier air. This thesis aims to investigate the modeling capabilities of MELCOR and STAR-CCM+ for small break air ingress events. Initial tests present a generic model to test the effects of forced flow and natural circulation through a break connecting a helium volume with an air volume. These tests range in diameters covering large breaks and sizing down to small breaks. The generic models provide a basis for confidence when modeling experimental results from literature, while testing the impact of break diameter, break length, and break orientation. When modeling the small breaks in MELCOR and STAR-CCM+, good agreement is seen between both codes and experimental values for larger diameters, but both codes show lower accuracy for smaller diameter cases when attempting to replicate the experimental results. To test the reason for disagreement, an investigation into the diffusive effects is carried out. The simulation setup, parameter sensitivity, and current limitations are discussed for both codes. Future work is needed to model the combination of buoyancy and diffusive forces correctly in MELCOR and STAR-CCM+. Further studies should also test the extensibility of MELCOR for cases beyond the current break orientation limit.","abstract_html":"In a High Temperature Gas-cooled Reactor (HTGR), the study of postulated accident scenarios is necessary for licensing, deployment, and public perception. One specific scenario of concern is the air ingress following a primary loop break. Recent research has determined that small breaks are more likely than large double-ended guillotine breaks. The primary driving mechanism for the air ingress is the buoyant force due to the density differences of helium and air. This leads to a stratified flow through the break, with the lighter helium flowing above the heavier air. This thesis aims to investigate the modeling capabilities of MELCOR and STAR-CCM+ for small break air ingress events. Initial tests present a generic model to test the effects of forced flow and natural circulation through a break connecting a helium volume with an air volume. These tests range in diameters covering large breaks and sizing down to small breaks. The generic models provide a basis for confidence when modeling experimental results from literature, while testing the impact of break diameter, break length, and break orientation. When modeling the small breaks in MELCOR and STAR-CCM+, good agreement is seen between both codes and experimental values for larger diameters, but both codes show lower accuracy for smaller diameter cases when attempting to replicate the experimental results. To test the reason for disagreement, an investigation into the diffusive effects is carried out. The simulation setup, parameter sensitivity, and current limitations are discussed for both codes. Future work is needed to model the combination of buoyancy and diffusive forces correctly in MELCOR and STAR-CCM+. Further studies should also test the extensibility of MELCOR for cases beyond the current break orientation limit.","abstract_has_math":false,"creators":["Boyd, Anthony Joel"],"institution":"University of Illinois Urbana-Champaign","degree_name":"M.S.","degree_level":"Thesis","degree_discipline":"Nuclear, Plasma, Radiolgc Engr","degree_department":null,"school":null,"contributors":["Brooks, Caleb S","Grunloh, Timothy P","Kozlowski, Tomasz"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2025,"date_issued":"2025-12","date_published":"2025-12","updated_at":"2026-07-22T22:25:07Z","subjects":["Stratified Flow","Computational Fluid Dynamics","System Analysis"],"languages":["en"],"rights":["Copyright 2025 Anthony Joel Boyd"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/132595","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Brooks, Caleb S","Grunloh, Timothy P","Kozlowski, Tomasz"]},{"key":"dc:creator","label":"Author","values":["Boyd, Anthony Joel"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2025-12","2025-12-09"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Nuclear, Plasma, Radiolgc Engr"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Thesis"]},{"key":"thesis:degree_name","label":"Degree Name","values":["M.S."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Stratified Flow","Computational Fluid Dynamics","System Analysis"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2025 Anthony Joel Boyd"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/132595"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["In a High Temperature Gas-cooled Reactor (HTGR), the study of postulated accident scenarios is necessary for licensing, deployment, and public perception. One specific scenario of concern is the air ingress following a primary loop break. Recent research has determined that small breaks are more likely than large double-ended guillotine breaks. The primary driving mechanism for the air ingress is the buoyant force due to the density differences of helium and air. This leads to a stratified flow through the break, with the lighter helium flowing above the heavier air. This thesis aims to investigate the modeling capabilities of MELCOR and STAR-CCM+ for small break air ingress events. Initial tests present a generic model to test the effects of forced flow and natural circulation through a break connecting a helium volume with an air volume. These tests range in diameters covering large breaks and sizing down to small breaks. The generic models provide a basis for confidence when modeling experimental results from literature, while testing the impact of break diameter, break length, and break orientation. When modeling the small breaks in MELCOR and STAR-CCM+, good agreement is seen between both codes and experimental values for larger diameters, but both codes show lower accuracy for smaller diameter cases when attempting to replicate the experimental results. To test the reason for disagreement, an investigation into the diffusive effects is carried out. The simulation setup, parameter sensitivity, and current limitations are discussed for both codes. Future work is needed to model the combination of buoyancy and diffusive forces correctly in MELCOR and STAR-CCM+. Further studies should also test the extensibility of MELCOR for cases beyond the current break orientation limit.","Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2026-02-19 without embargo terms","The student, Anthony Boyd, accepted the attached license on 2025-12-08 at 20:56.","The student, Anthony Boyd, submitted this Thesis for approval on 2025-12-08 at 21:06.","This Thesis was approved for publication on 2025-12-09 at 09:25.","DSpace SAF Submission Ingestion Package generated from Vireo submission #23107 on 2026-02-19 at 18:30:09"]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Investigation of MELCOR and STAR-CCM+ modeling capabilities to accurately predict air ingress rates from small breaks in high temperature gas-cooled reactors"]}]}],"canonical_facts":{"dc:contributor":["Brooks, Caleb S","Grunloh, Timothy P","Kozlowski, Tomasz"],"dc:creator":["Boyd, Anthony Joel"],"dc:date":["2025-12","2025-12-09"],"dc:description":["In a High Temperature Gas-cooled Reactor (HTGR), the study of postulated accident scenarios is necessary for licensing, deployment, and public perception. One specific scenario of concern is the air ingress following a primary loop break. Recent research has determined that small breaks are more likely than large double-ended guillotine breaks. The primary driving mechanism for the air ingress is the buoyant force due to the density differences of helium and air. This leads to a stratified flow through the break, with the lighter helium flowing above the heavier air. This thesis aims to investigate the modeling capabilities of MELCOR and STAR-CCM+ for small break air ingress events. Initial tests present a generic model to test the effects of forced flow and natural circulation through a break connecting a helium volume with an air volume. These tests range in diameters covering large breaks and sizing down to small breaks. The generic models provide a basis for confidence when modeling experimental results from literature, while testing the impact of break diameter, break length, and break orientation. When modeling the small breaks in MELCOR and STAR-CCM+, good agreement is seen between both codes and experimental values for larger diameters, but both codes show lower accuracy for smaller diameter cases when attempting to replicate the experimental results. To test the reason for disagreement, an investigation into the diffusive effects is carried out. The simulation setup, parameter sensitivity, and current limitations are discussed for both codes. Future work is needed to model the combination of buoyancy and diffusive forces correctly in MELCOR and STAR-CCM+. Further studies should also test the extensibility of MELCOR for cases beyond the current break orientation limit.","Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2026-02-19 without embargo terms","The student, Anthony Boyd, accepted the attached license on 2025-12-08 at 20:56.","The student, Anthony Boyd, submitted this Thesis for approval on 2025-12-08 at 21:06.","This Thesis was approved for publication on 2025-12-09 at 09:25.","DSpace SAF Submission Ingestion Package generated from Vireo submission #23107 on 2026-02-19 at 18:30:09"],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/132595"],"dc:language":["en"],"dc:rights":["Copyright 2025 Anthony Joel Boyd"],"dc:subject":["Stratified Flow","Computational Fluid Dynamics","System Analysis"],"dc:title":["Investigation of MELCOR and STAR-CCM+ modeling capabilities to accurately predict air ingress rates from small breaks in high temperature gas-cooled reactors"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Nuclear, Plasma, Radiolgc Engr"],"thesis:degree_level":["Thesis"],"thesis:degree_name":["M.S."],"thesis:institution_name":["University of Illinois Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:07Z"}