1. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 1 A PHOENICS model of the hotbox region of an advanced gas-cooled nuclear reactor by G Hulme NNC Ltd

2. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 2 Content of presentation Description of the problem Description of the problem Description of the PHOENICS model Description of the PHOENICS model –mesh –modelling of complex standpipe region Results for three cases are presented Results for three cases are presented Comparison against experimental measurements Comparison against experimental measurements –velocity field –trace gas concentration

3. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 3 The AGR hotbox region Hot gas from reactor fuel channels mixes before entering boilers Hot gas from reactor fuel channels mixes before entering boilers Geometry Geometry –cylindrical –square array of 332 fuel channel standpipes at centre –outer ring of 12 boilers –gas baffle dome NNC 1/8th scale model NNC 1/8th scale model

4. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 4 Side view of NNC 1/8th scale model

5. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 5 Plan view of hotbox

6. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 6 PHOENICS model Cylindrical domain with multi-block mesh Cylindrical domain with multi-block mesh Uses GCV method to solve for Uses GCV method to solve for –pressure, –3 velocity components, –k- turbulence model, –trace gas concentration SMART higher-order scheme for velocities and concentration SMART higher-order scheme for velocities and concentration Initial development on single-quadrant model Initial development on single-quadrant model Extended to 4-quadrant model Extended to 4-quadrant model

7. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 7 Computational mesh Multi-block mesh with body-fitted co-ordinates Multi-block mesh with body-fitted co-ordinates Central square block allows modelling of standpipes Central square block allows modelling of standpipes Outer blocks allow fitting of mesh to boilers and outer shell Outer blocks allow fitting of mesh to boilers and outer shell Single-quadrant 3-block model Single-quadrant 3-block model 4-quadrant 5-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. Mesh is generated by SATELLITE inter-active facility followed by modification of XYZ files by specially written programs.

8. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 8 Single quadrant mesh - block arrangement Boiler 5 Boiler 7 Boiler 6 Block 1 Block 3 Block 2

9. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 9 Mesh in horizontal plane, single quadrant model

10. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 10 Modelling of standpipe region Approximate model of a complex region Approximate model of a complex region Each standpipe modelled by 3 3 array of cells Each standpipe modelled by 3 3 array of cells Mesh areas adjusted to match area of inlet jets Mesh areas adjusted to match area of inlet jets Cross-flow pressure drop modelled by resistance sources with directional magnitude Cross-flow pressure drop modelled by resistance sources with directional magnitude Turbulence modelling Turbulence modelling –source term for k making k~0.28v 2 – set to give length scale based on passage width so that L = 0.1(P-D)

11. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 11 Mesh in vertical plane through standpipe region

12. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 12 Mesh for 4 quadrant model

13. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 13 Calculations performed A1Symmetrical operation with trace gas injection at a single standpipe using single-quadrant model A1Symmetrical 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 A2 Symmetrical operation with enhanced flow from a single empty channel using single-quadrant model B3-quadrant operation using the 4-quadrant model with a coarse mesh. B3-quadrant operation using the 4-quadrant model with a coarse mesh.

14. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 14 Results - Symmetrical operation, Vectors in plane between boilers

15. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 15 Results - Symmetrical operation, Vectors in plane through a boiler

16. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 16 Results - Symmetrical operation, Vectors in horizontal plane below boiler inlet

17. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 17 Comparison of radial velocity profiles in plane between boilers

18. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 18 Comparison of radial velocity profiles in plane through a boiler

19. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 19 Discussion of results - velocity Flow pattern well represented Flow pattern well represented Velocity fields in reasonable agreement with measurements Velocity fields in reasonable agreement with measurements Main discrepancy is underprediction of velocity of jet from top of standpipe region Main discrepancy is underprediction of velocity of jet from top of standpipe region Causes Causes –smearing of velocity distribution downstream of standpipes –modelling of standpipe region flow distribution

20. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 20 Results - Symmetrical operation, Trace gas injection at one standpipe

21. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 21 Comparison of trace gas concentration profiles

22. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 22 Results - symmetrical operation with empty channel flow

23. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 23 Discussion of results - concentration Trace gas plume fairly well modelled Trace gas plume fairly well modelled Main discrepancy Main discrepancy –plume slightly too low –diffusion slightly too weak. Causes 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 Distribution of empty channel flow at boilers is well predicted

24. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 24 Results - asymmetrical 3-quadrant operation

25. Adding value through knowledge © NNC Limited September 2002International PHOENICS User Conference 25Conclusion A PHOENICS model of the AGR hotbox region has been described. A PHOENICS model of the AGR hotbox region has been described. The model uses a multi-block mesh with body-fitted co- ordinates. The model uses a multi-block mesh with body-fitted co- ordinates. An approximate model of the complex standpipe region is used. An approximate model of the complex standpipe region is used. It has been shown that the model gives reasonably good representations of 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. The extension of the model to a four-quadrant asymmetric case has been demonstrated.