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A PHOENICS model of the hotbox region of an advanced gas-cooled nuclear reactor

A PHOENICS model of the hotbox region of an advanced gas-cooled nuclear reactor. by G Hulme NNC Ltd. Content of presentation. Description of the problem Description of the PHOENICS model mesh modelling of complex standpipe region Results for three cases are presented

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A PHOENICS model of the hotbox region of an advanced gas-cooled nuclear reactor

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  1. A PHOENICS model of the hotbox region of an advanced gas-cooled nuclear reactor by G Hulme NNC Ltd International PHOENICS User Conference

  2. Content of presentation • Description of the problem • Description of the PHOENICS model • mesh • modelling of complex standpipe region • Results for three cases are presented • Comparison against experimental measurements • velocity field • trace gas concentration International PHOENICS User Conference

  3. The AGR hotbox region • Hot gas from reactor fuel channels mixes before entering boilers • Geometry • cylindrical • square array of 332 fuel channel standpipes at centre • outer ring of 12 boilers • gas baffle dome • NNC 1/8th scale model International PHOENICS User Conference

  4. Side view of NNC 1/8th scale model International PHOENICS User Conference

  5. Plan view of hotbox International PHOENICS User Conference

  6. PHOENICS model • Cylindrical domain with multi-block mesh • Uses GCV method to solve for • pressure, • 3 velocity components, • k- turbulence model, • trace gas concentration • SMART higher-order scheme for velocities and concentration • Initial development on single-quadrant model • Extended to 4-quadrant model International PHOENICS User Conference

  7. Computational mesh • Multi-block mesh with body-fitted co-ordinates • Central square block allows modelling of standpipes • Outer blocks allow fitting of mesh to boilers and outer shell • Single-quadrant 3-block model • 4-quadrant 5-block model • Mesh is generated by SATELLITE inter-active facility followed by modification of XYZ files by specially written programs. International PHOENICS User Conference

  8. Single quadrant mesh - block arrangement Boiler 5 Boiler 6 Block 3 Boiler 7 Block 2 Block 1 International PHOENICS User Conference

  9. Mesh in horizontal plane, single quadrant model International PHOENICS User Conference

  10. Modelling of standpipe region • Approximate model of a complex region • Each standpipe modelled by 33 array of cells • Mesh areas adjusted to match area of inlet jets • Cross-flow pressure drop modelled by resistance sources with directional magnitude • Turbulence modelling • source term for k making k~0.28v2 •  set to give length scale based on passage width so that L = 0.1(P-D) International PHOENICS User Conference

  11. Mesh in vertical plane through standpipe region International PHOENICS User Conference

  12. Mesh for 4 quadrant model International PHOENICS User Conference

  13. Calculations performed • A1 Symmetrical operation with trace gas injection at a single standpipe using single-quadrant model • A2 Symmetrical operation with enhanced flow from a single empty channel using single-quadrant model • B 3-quadrant operation using the 4-quadrant model with a coarse mesh. International PHOENICS User Conference

  14. Results - Symmetrical operation, Vectors in plane between boilers International PHOENICS User Conference

  15. Results - Symmetrical operation, Vectors in plane through a boiler International PHOENICS User Conference

  16. Results - Symmetrical operation, Vectors in horizontal plane below boiler inlet International PHOENICS User Conference

  17. Comparison of radial velocity profiles in plane between boilers International PHOENICS User Conference

  18. Comparison of radial velocity profiles in plane through a boiler International PHOENICS User Conference

  19. Discussion of results - velocity • Flow pattern well represented • Velocity fields in reasonable agreement with measurements • Main discrepancy is underprediction of velocity of jet from top of standpipe region • Causes • smearing of velocity distribution downstream of standpipes • modelling of standpipe region flow distribution International PHOENICS User Conference

  20. Results - Symmetrical operation, Trace gas injection at one standpipe International PHOENICS User Conference

  21. Comparison of trace gas concentration profiles International PHOENICS User Conference

  22. Results - symmetrical operation with empty channel flow International PHOENICS User Conference

  23. Discussion of results - concentration • Trace gas plume fairly well modelled • Main discrepancy • plume slightly too low • diffusion slightly too weak. • Causes • velocity field in jet from standpipe region • turbulence level in flow leaving standpipe region • Distribution of empty channel flow at boilers is well predicted International PHOENICS User Conference

  24. Results - asymmetrical 3-quadrant operation International PHOENICS User Conference

  25. Conclusion • A PHOENICS model of the AGR hotbox region has been described. • The model uses a multi-block mesh with body-fitted co-ordinates. • An approximate model of the complex standpipe region is used. • It has been shown that the model gives reasonably good representations of • the velocity field • the trace gas concentration fields. • The extension of the model to a four-quadrant asymmetric case has been demonstrated. International PHOENICS User Conference

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