Multi-dimensional simulation of hydrogen distribution and turbulent combustion in severe accidents

Abstract

The work performed within this project was supported by EC in the 4th Framework Programme. Multidimensionale Simulation von Verteilung und TurbulenterVerbrennung Multidimensional Simulation of Hydrogen Distribution and Turbulent Combustion in Severe Accidents ABSTRACTThe design and assessment of hydrogen mitigating systems in a nuclear power plant needs the detailed simulation with high spatial resolution of the major physical processes including hydrogen source terms, distribution, ignition, and combustion, taking into account local gas conditions. The present project in the 4 1 h EU Framework Programmedeals with the development and verification of physical and numerical models that can be used in multidimensional CFD codes, which solve the general equations of reactive fluid dynamics. The objective of the joint research programme was to develop CFD-models for hydrogen distribution, turbulent combustion, and hydrogen mitigation techniques, which can be applied to risk reduction in current and future nuclear power plants. The work programme consisted, firstly, of an experimental part with tests suitable to provide a data base, secondly, of modeling and Validation work, and thirdly, of application of the validated numerical tools to full-scale demonstration cases.In two small scale facilities at the Lehrstuhl A für Thermodynamik, Technical University of Munich (TUM), experiments provided data over a wide range of flame regimes, including the interaction of the flame front with obstacle configurations. A medium scale test facility at the Forschungzentrum Karlsruhe (FZK) provided data on turbulent combustion in the range of medium fast turbulent deflagrations up to detonation velocity. In inert tests, the conditions after a propagating shock wave through an obstacle path were also investigated. In addition, results of large-scale tests performed in the RUT facility at the Kurchatov Institute (KI) have been used for model verification. It was concluded, that incomplete combustion is not possible for dry mixtures with more than 10.5 vol-% hydrogen and that results depend weakly on obstacle spacing. Further, three phases in the combustion process can be distinguished: a slow acceleration phase is followed by a fast one, later the flame propagates with constant velocity in the tubes with repeated obstacles.The numerical tools involved in this project are COM3D and GASFLOW at FZK, REACFLOW at Joint Research Centre Ispra (JRC), TONUS at Commissariat a !'Energie Atomique (CEA) and models implemented in CFX4.2 at TUM. The codes were verified in a two-step approach. Firstly, each code was tested against standard test cases and against different experiments. Secondly, the codes were used to calculate a common set of experiments. These benchmark calculations allowed a direct comparison of the different numerical models and implementations. Model applications were a) TONUS simulation of H2-steam distribution and combustion in four-compartment geometry, b) GASFLOW simulation of the Battelle Helium injection test Hyjet Jx7 and ...

Advanced Numerical Simulation for the Safety Demonstration of Nuclear Power Plants

“…Nevertheless, selected efforts could be devoted to improving the computation features of the transient parts where the geometry-related effects are widely dominant on the physical uncertainties. In such situations, CFD codes can give interesting results, and in fact they are becoming more and more widely used in problems like the hydrogen repartition and combustion in the containment (TONUS code jointly developed by CEA and IRSN (Bielert et al, 2001)) or the corium pool behavior in the vessel bottom, or the corium spreading and solidification process out of the vessel (CROCO code developed by IRSN (Gastaldo et al, 2006)). The multi-scale approach has tentatively been adopted at IRSN to investigate the physical phenomena in the regions where the solid particles form a porous bed of debris and where the molten materials build up and accumulate, forming a molten pool (Roux et al 2006).…”

Assessment of CFD Codes Used in Nuclear Reactor Safety Simulations

“…There have been many applications of compressible CFD solvers to model detonations in large-scale geometries: for example, the RUT experiments from the Kurchatov Institute [40], also some calculations of fast deflagrations in a simplified EPR (European Pressurised Water Reactor) containment were performed in the framework of the 5 th FWP Project HYCOM [41]. Hydrogen deflagration models and CFD codes were also evaluated in the 4 th EU FWP programme HDC [42].…”

The reactive Riemann problem for thermally perfect gases at all combustion regimes

“…Concluding, our final purpose is the solution of the system of equation (4). The dependent variables are , w, ẽ t , Y j,i ( j = H 2 , O 2 , H 2 O) and .…”