Numerical modelling of direct contact condensation of steam in BWR pressure suppression pool system Gitesh Patel, Vesa Tanskanen, Juhani Hyvärinen LUT School of Energy Systems/Nuclear Engineering, Lappeenranta University of Technology, Finland Nuclear Science & Technology Symposium - NST2016 Helsinki, Finland, 2-3 Nov. 2016
Outlines Motivation Objective POOLEX facility Numerical models and simulations details Results Summary Current work Gitesh Patel Nuclear Engineering, LUT, Finland 2
Motivation In a BWR, the suppression pool is one of the key safety systems during a loss of coolant accident (LOCA) or safety valve actuation. Suppression pool provides a large pressure and heat sink by condensing vapor into liquid and absoring the energy disharge from a reactor vessel. (a) http://www.tvo.fi/uploads/file/nuclear-power-plant-units.pdf Gitesh Patel Containment (a) Nuclear Engineering, LUT, Finland 3
Motivation (cont.) The sub-cooling of the pool liquid and the mass flux of injected vapor determine the character of occuring of direct contact condensation (DCC). Schematic of typical regions for condensation modes during SRV or LOCA blowdown in BWR (a) Injected steam interacts with pool water by heat transfer, rapid condensation and momentum exchange, inducing hydrodynamics loads to the pool structures. (a) R. Lahey, and F. Moody, (1993). The Thermal-Hydraulics of a Boiling Water Reactor, 2nd edn. American Nuclear Society. Gitesh Patel Nuclear Engineering, LUT, Finland 4
Objective To implement two-phase solver of OpenFOAM CFD code To simulate DCC phenomena appearing in BWR suppression pools Validation of results Gitesh Patel Nuclear Engineering, LUT, Finland 5
POOLEX facility The POOLEX (Condensation Pool Experiment) test facility was a scaled down representation of a suppression pool wetwell. POOLEX (a) (a) Laine, J. and Puustinen, M., (2006), Condensation Pool Experiments with Steam using Insulated DN200 Blowdown Pipe, Research report POOLEX 03/2005, LUT. Gitesh Patel Nuclear Engineering, LUT, Finland 6
POOLEX facility: STB-28 test The STB-28 test was aimed to investigate steam bubble formulation and its condensation at the blowdown pipe outlet as a function of pool water temperature. During the blowdown, seven short time intervals in the range of 12 s to 30 s were recorded with a higher sampling rate. These sub tests were labelled from STB-28-1 to STB-28-7. Gitesh Patel Nuclear Engineering, LUT, Finland 7
Numerical models and simulations details Eulerian-Eulerian two-fluid approach was used in OpenFOAM. (Continuity Eq.) (Momentum Eq.) Flow turbulence was solved by employing the k-ε turbulence model. (Energy Eq.) PIMPLE (PISO-SIMPLE) pressure velocity coupling algorithm was applied. Gitesh Patel Nuclear Engineering, LUT, Finland 8
Numerical models and simulations details (cont.) The interfacial heat fluxes were solved as, Q HTC T S T i, H i, i, HTC Nu L t i, a i, b HTC i, a T T HTC T T S H i, b a H i, a i, b S b (a) Hughes and Duffey (1991) Nu 2 Re t 1 2 Pr Re t bvt L b t 1 3 4 1 L 4 t v t () (a) Hughes, E.D., Duffey, R.B., (1991). Direct contact condensation and momentum transfer in turbulent separated flows. Int. J. Multiphase Flow 17, 599-619 Gitesh Patel Nuclear Engineering, LUT, Finland 9
Numerical models and simulations details (cont.) Test conditions (STB28-4): steam temperature: 379.1 K; water temperature: 340.5 K; steam mass flow rate at inlet: 0.238 kg/s; water in the pool: hydrostatic pressure; steam-water interface at t=0 s: 0.76 m in the pipe. 3D grid 2D-axisymetric grid 2D-axisymmetric grid contains 45626 hexahedral cells. Full 3D grid contains 302796 hexahedral cells. Gitesh Patel Nuclear Engineering, LUT, Finland 10
Results Grid Convergence Index (GCI) method was used. Relative error Extrapolated relative error Grid Convergence Index (GCI) Condensation mass flow rate Interfacial area Gitesh Patel Nuclear Engineering, LUT, Finland 11
Results (cont.) STB-28 experiment STB-28-4 (OpenFOAM) Gitesh Patel Nuclear Engineering, LUT, Finland 12
Results (cont.) 2D results OpenFOAM (incompressible solver) OpenFOAM (compressible solver) NEPTUNE_CFD (V. Tanskanen, 2012) Gitesh Patel Nuclear Engineering, LUT, Finland 13
Results (cont.) 2D results The incompressible is inadequate for chugging simulations. The DCC rate in the OpenFOAM simulations is relatively high than to the DCC rate of NEPTUNE _CFD simulations. Visually, the chugging frequency is higher but the amplitude of interface position in blowdown pipe is lower in the OpenFOAM case than in the NEPTUNE_CFD simulations. Gitesh Patel Nuclear Engineering, LUT, Finland 14
Results (cont.) Penetration of the initial steam jet 3D results Eruption and collapse of the bubble after the steam jet penetration Gitesh Patel Nuclear Engineering, LUT, Finland 15
Current work PPOOLEX simulations (DCC-05-4 test) 2D-axisymetric grid 72089 hexahedral cells. Gitesh Patel Nuclear Engineering, LUT, Finland 16
Summary The suppression pool is one of the key safety systems of BWR containment. Two-phase flow solver of OpenFOAM CFD code was implemented. The HD DCC model based on surface renewal model was employed. As the reference, the steam blowdown tests of the suppression pool test facilities of Lappeenranta University of Technology were used. Previously simulated results of NEPTUNE_CFD code were utilised for the assessment of OpenFOAM simulations. The qualitative and quantitate behavior of the steam-water interface agreed well to the test results in the simulations with the OpenFOAM and NEPTUNE_CFD CFD solvers. An adequate grid size and compressible solver are crusial for chugging simulations. Gitesh Patel Nuclear Engineering, LUT, Finland 17
Acknowledgements The research leading to these results was funded by the Finnish Nuclear Waste Management Fund (VYR) via SAFIR2014 and SAFIR2018, and Doctoral Programme for Nuclear Engineering and Radiochemistry (YTERA). Gitesh Patel Nuclear Engineering, LUT, Finland 18
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