computational fluid dynamics (cfd) for nuclear reactor ... carbon energy/nuclear energy... ·...
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Computational Fluid Dynamics (CFD) for nuclear reactor safety assessment
SolutionsVTT offers CFD solutions in a wide range of applications in nuclear reactor safety assessment, including:• Spreading of hydrogen in containment, deflagration and
detonation• Mixing and stratification of hot and cold water in pipelines
and pressure vessel; analysis of thermal fatigue• CFD simulation of steam generators; coupled CFD−
system code simulation of loss of feed water, loss of offsite power, break of steam line etc.
• Fluid-Structure Interactions (FSI), pressure loads and strains caused by pipe breaks
• Behavior of pressure suppression pools of BWRs during large-break LOCA
• Fires in containments, turbine halls or cable tunnels• Modeling boiling, wall and bulk condensation and
direct-contact condensation
ValidationThe codes and models that are used have been validated by participating in international bench-mark exercises and national programmes:• Condensation of vapor in vapor-air mixture on vertical
walls (CONAN & MISTRA experiments, OECD-NEA SARnet programme)
• Erosion of stratification of hydrogen and helium by vertical steam jet (OECD-NEA THAI & HYMERES projects)
• Deflagration of hydrogen (THAI project)• Spray benchmark (SARnet-2 programme)• Pressure drop and pressure rise in steam generators
(PWR PACTEL, LUT Energy)• BWR large-break LOCA experiments (PPOOLEX facility,
LUT Energy)
CodesWe use ANSYS Fluent®, OpenFOAM® and the in-house code PORFLO to solve the flow equations with user-defined submodels for boiling and condensation. The CFD codes can be coupled with FEM and system codes.
Computational Fluid Dynamics (CFD) are increasingly used in Nuclear Reactor Safety (NRS) assessment. Many phenomena in NRS assessment are inherently three-dimensional and one-dimensional solutions are not sufficient. In CFD calculations, proper validation of the numerical methods and experienced users of the codes are essential in obtaining reliable results. VTT has a high level expertise in single phase and multiphase CFD calculations by using numerical tools validated in inter-national OECD-NEA benchmark exercises. The CFD codes can be run in computer clusters with several hundreds of CPU cores.
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Timo Pättikangas, Principal ScientistTel. +358 40 595 [email protected]
Additional information
Mikko Ilvonen, Principal ScientistTel. +358 40 595 [email protected]
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Example: Spreading of hydrogen in a PWR containmentA postulated Loss Of Coolant Accident (LOCA) was ana-lyzed for a PWR. The hydrogen produc-tion in the reac-tor core was calculated by using the severe accident code MELCOR. The sprea-ding of hydrogen and steam including conden-sation were calculated with ANSYS Fluent.
Mole fraction of hydrogen in a PWR containment during a postulated severe accident at two instants of time.
Example: Fluid−Structure Interactions (FSI)The motion and the stresses of the internals of the pres-sure vessel have been calculated during pressure transient caused by pipe break near the pressure vessel. The vali-dation of the two-way coupled CFD-FEM calculations has been done against German HDR experiments.
Stresses and deformations (200) of the internals of the pressure vessel. Two-way coupled CFD-FEM calculation of Large-Break Loss Of Coolant Accident (LB-LOCA).
Example: EPR steam generatorEPR steam generator has been analyzed during postulated Loss Of Offsite Power (LOOP) transient. The behavior of the NPP was first calculated with the Apros system code. The Apros result was used as the boundary condition in the CFD simulation of the secondary side of the steam generator. In the CFD model, the primary tubes were described as porous media.
Void fraction in an EPR steam generator during postulated Loss Of Offsite Power transient. The effects of the isolation of the steam line and opening the relief valve are shown.
Example: CFD-neutronics-system- couplingContinuous development of dedicated in-house codes HEXTRAN (neutronics), SMABRE (plant system) and PORFLO (3D TH / CFD) facilitates coupled multi-disciplinary simulations.
Assembly-wise power profile (left) and RPV coolant tempera-ture (right) of a VVER-440 plant at time 40 s in the AER-7 benchmark transient.
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t = 5.0 s 7.5 s 12.5 s 17.5 s 25.0 s
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0.5
0.75
0.25
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Ilona Lindholm, Key Account ManagerTel. +358 40 593 [email protected]
VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTDwww.vttresearch.com