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Abstract
The severe reactor accident at Fukushima Daiichi Nuclear Power Plant (2011) has confirmed the need to understand the flow and transport processes of steam and combustible gases inside the containment and connected buildings. Over several years, Computational Fluid Dynamics (CFD) models, mostly based on proprietary solvers, have been developed to provide highly resolved insights; supporting the assessment of effectiveness of safety measures and possible combustion loads challenging the containment integrity. This paper summarizes the design and implementation of containmentFOAM, a tailored solver and model library based on OpenFOAM®. It is developed in support of Research & Development related to containment flows, mixing processes, pressurization, and assessment of passive safety systems. Based on preliminary separate-effect verification and validation results, an application oriented integral validation case is presented on the basis of an experiment on gas mixing and H2 mitigation by means of passive auto-catalytic recombiners in the THAI facility (Becker Technologies, Eschborn, Germany). The simulation results compare well with the experimental data and demonstrate the general applicability of containmentFOAM for technical scale analysis. Concluding the paper, the strategy for dissemination of the code and measures implemented to minimize potential user errors are outlined.
Highlights
The containmentFOAM package consists of primarily two major parts, the tailored solver (Section 2.1) and model library (Section 2.2), which are summarized in the following
Besides passive auto-catalytic Hydrogen recombiners (PAR), there are other safety relevant technical components to be considered in a containment-scale application, e.g., the opening of pressure relief flaps and doors is modeled on basis of an arbitrary mesh interface (AMI), which opens depending on a differential pressure condition
The dedicated Computational Fluid Dynamics (CFD) simulation tool containmentFOAM for the analysis of transport and mixing phenomena inside the containment and connected buildings of a nuclear reactor is developed based on the open source CFD toolbox OpenFOAM®
Summary
The local formation of a flammable gas mixture can result in dynamic combustion loads, which may challenge the integrity of the containment, its internal structures, and safety systems To assess both pressurization paths, the 3D distribution of steam and non-condensable gases needs to be analyzed. The density difference causing buoyant flows are either due to mass concentration gradients of the multicomponent gas mixture or temperature gradients due to conjugate heat transfer (convection and wall condensation), thermal radiation, local heat sinks, and sources (e.g., decay heat by aerosol transport, bulk condensation) Besides these physical phenomena, safety systems, e.g., passive auto-catalytic Hydrogen recombiners (PAR) or containment coolers interact with the surrounding containment atmosphere and introduce density differences.
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