1. Control Rod Nozzle Guide Tubes improved by 4 drilled holes. Model as two coaxial tubes of fluid connected by 4 holes. Two inlets at the bottom from the same body of fluid. One outlet at the top and one blockage 12

2. 2D meshes as a first approximation Model as a cross section through the coaxial tubes coincident with the connecting holes. 3 refinements: very coarse, 2X refinement and 4X refinement.

3. Test of the pressure inlet in Code Saturne. Velocity distribution. Top – reference velocity is used to find the flow. Bottom – the inlet pressures and outlet pressures were read from the results and set as pressure Dirichlet boundary conditions, velocity was a Neumann boundary condition equal to 0.

4. Test of the pressure inlet. Velocity flow feature.

5. Test of the pressure inlet. Pressure distribution and profile across the inlets. Turbulent energy distribution

6. Using the test case pressure inlet boundary conditions Very coarse Coarse Refined Flow feature, much less flowing through the hole so not as dramatic as before. 40.6 bar38.5 bar

7. Velocities across the inlets and outlet Inlets velocity, left – unblocked, right – blocked. Outlet velocity, skewed towards the left. For the refined mesh the inlets and outlet velocities are shown.

8. Mass flows across the inlets and outlet Inner inlet mass flow against refinements 1, 2 and 4. Outer inlet mass flow against refinements 1, 2 and 4. Outlet inlet mass flow against refinements 1, 2 and 4.

9. Semi 3D model. Model as 2 parallel blocks of fluid, an unfurled cylinder. Meshing of the connecting hole. Coarse meshing of the geometry, also created 2X and 4X refinement meshes.

10. Inlets and Outlet velocity profile across the same line as before. Inlets velocity. Left – unblocked, mass flow is 9.34kgs-1, right – blocked, mass flow is 0.03Kgs-1. Outlet velocity, mass flow is 9.37Kgs-1.

11. Inlets and Outlet velocity perpendicular to previous. Very coarse Coarse Inlet Outlet

12. Further investigation Using the refined mesh Testing different turbulence models Further verification and validation investigations Creating and testing a fully 3D model (below)