NEPTUNE_CFD is a code based on a 3D transient Eulerian two-fluid model. One of the main application targets is the two-phase Pressurized Thermal Shock (PTS), which is related to PWR Reactor Pressure Vessel (RPV) lifetime safety studies, when sub-cooled water from Emergency Core Cooling (ECC) system is injected into the possibly uncovered cold leg and penetrates into the RPV downcomer. Five experiments were selected for the validation. A co-current smooth and wavy airwater stratified flow in a rectangular channel with detailed measurements of turbulence and velocities allows to validate the dynamic models. A co-current smooth and wavy steam-water stratified flow in a rectangular channel with measurements of the steam flow rates allows to validate the condensation models. Two experiments dealing with a water jet impingement on a water pool free surface in air environment allow to validate the dynamic models in the situation of a jet impinging a pool free surface. Finally, the COSI experiment allows to validate all the models involved in the reactor conditions. The calculations are done with the same set of Large Interface Method (LIM) models and a RANS (k-ε) approach for turbulence. They substantiate the application of the tool to PTS studies.
A new 3-D model has been developed to describe the interaction between a transferred electric arc and a liquid metal bath, and has been used to simulate a pilot axisymmetrical transferred arc furnace operating in the EDF Research and Development laboratory.This model enables calculations of the flow patterns, temperature distribution and electromagnetic fields in both the arc and the bath. The Navier-Stokes equation coupled with the electromagnetic relations are solved in each domain using a finite volume method. The source term in the radiative energy equation is modeled using the radiative transfer method in order to take into account the strong temperature variations in the electric arc. The transport and condensation of metal vapour in the arc domain are considered by solving a conservation equation for the vapour mass fraction. The arc flow calculation at the bath surface uses a one-dimensional sheath model taking account of the metal vapour, in order to ensure the coupling between the plasma and the bath by evaluating the boundary conditions at the arc/bath interface. The calculations were performed for an arc length of 0.25 m.Realistic predictions are obtained for the electrical, dynamic and thermal behaviour of the plasma and liquid metal, and also for the arc voltage. The results indicate that the effects of the arc impact and Lorentz forces are not sufficient to induce effective mixing throughout the metal bath, leading to a marked thermal stratification in the liquid metal. In the bath, the liquid/solid interface has been determined by calculations.
The multifield computational fluid dynamics (CFD) code NEPTUNE_CFD is applied to carry out a numerical study of the steady-state subchannel test-case of the OECD/NRC NUPEC PWR subchannel and bundle tests (PSBTs) international benchmark, focusing on the simulation of a subset of five selected experimental runs of the centered subchannel configuration. First, using a standard choice for the physical models and a constant, predetermined bubble diameter, the calculated void fraction is compared to experimental data. Besides, the mesh sensitivity of the calculated void fraction is investigated by performing simulations of three grid levels, and the propagation of the experimental uncertainties on the input parameters of the simulations is also studied. Last, calculation results with devoted models for the bubble-size distribution are analyzed. Their impact is visible on the subcooled run, giving void fraction closer to experiments than those obtained with a fixed bubble-size. Void-fraction distribution with bubble-size models is also shown to come closer to experiment for another run with a higher equilibrium quality.
The Atmospheric Radiation field has seen the development of more accurate and faster methods to take into account absorption. Modelling fog formation, where Infrared Radiation is involved, requires accurate methods to compute cooling rates. Radiative fog appears under clear-sky condition due to a significant cooling during the night where absorption and emission are the dominant processus. Thanks to High Performance Computing, high resolution multi-spectral approaches to solving the Radiative Transfer Equation are often used. Nevertheless, the coupling of three-dimensional radiative transfer with fluid dynamics is very computationally expensive. Radiation increases the computation time by around fifty percent over the pure Computational Fluid Dynamics simulation. To reduce the time spent in radiation calculations, a new method using analytical absorption functions fitted by Sasamori on Yamamoto's radiation chart has been developed to compute an equivalent absorption coefficient (spectrally integrated). Only one solution of Radiative Transfer Equation is needed against N band × N gauss for an N band model with N gauss quadrature points on each band. A comparison with simulation data has been done and the new parameterization of Radiative properties proposed in this article shows the ability to handle variations of gases concentrations and liquid water.
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