Magnetic field effects on liquid metal free convection

International audienceWe provide a numerical analysis of three-dimensional free convection of a liquid in a Rayleigh-Bénard configuration,subject to a steady and uniform magnetic field, using the finite volume code Jadim. The influence of the Hartmann andRayleigh numbers are studied. We compare our results to several experimental works. As suggested by previousexperiments, the magnetic field tends to lower the heat transfer at the walls. This is caused by a significant alteration ofthe flow structures, due to the Lorentz force. For slightly overcritical Rayleigh numbers, two-dimensional rolls appearbut the flow structure rapidly becomes three-dimensional as we increase the Rayleigh number. The magnetic field tendsto destroy those structures and the transition to a 3D flow is delayed to higher values of the Rayleigh number, when theHartmann number is increased. We show that the averaged heat transfer at the walls decreases, although it remains ofthe same order of magnitude. However the local structure of heat transfer is altered

Investigating a Chalcolithic gold bead from Mehrgarh (Balochistan). Hammering or casting process tracked by neutron diffraction texture analysis

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Hydrodynamic numerical simulations of a prototypical oxide-metal corium melt representative of fukushima 1-F1 severe accident conditions

International audienceIn the frame of Severe Accident studies, the VULCANO-facility at PLINIUS-platform (CEA - Cadarache) is devoted to the understanding of the interaction of corium with a concrete containment pit (Molten Corium Concrete Interaction-MCCI) [1]. The VULCANO VF-U1 experiment was designed to be closer as possible of the MCCI conditions possibly occurring in the Fukushima F1 reactor considering the coexistence of two dispersed phases (metallic liquid droplets and gaseous bubbles) in a continuous phase (oxide melt liquid).A MCCI industrial code was used to perform predictive calculation of the VF-U1 experiment, being closer as possible of Fukushima 1-F1 MCCI conditions. The results shown that the axial ablation is 8 times higher than the radial one. Then, a multiplicative factor of 8 for the axial heat exchange coefficient must be applied to find the final cavity shape. VULCANO VF-U1 Post-Test Analyses have shown that the metallic phase is preferably close to the vertical concrete walls and at the bottom of the test section whereas a stratification due to density difference between the oxide and the metallic phase is expected (as modeling by the MCCI code). Regarding to the real coupling physical effects in the integral the VULCANO-ICB test and the difficulties for the MCCI code to reproduce experimental behaviors, numerical simulations were conducted. For this purpose, a multiphase Volume Of Fluid (VOF) code at AMU (MADIREL) has been developed . In these calculations, the corium has been modelled numerically under isothermal conditions as a two-dimensional dispersed medium with multiple metal drops and gas bubbles. The results showed a possible hydrodynamic re-localization matching to experimental results

Towards an European consensus on possible causes of MCCI ablation anisotropy in an oxidic pool

International audienceOne of the most disputed issues raised by molten corium concrete interaction (MCCI) is how the 2D cavity ablation in an oxidic pool evolves why is the ablation anisotropic with siliceous concretes and isotropic with carbonaceous concretes. The work performed in the frame of the SARNET2 WP6 group during the last 4 years has enabled significant progress on this topic. This paper summarizes this progress using the analysis of recent 2D real material experiments in an oxidic pool and from analytical simulant experiments on 2D heat convection in a bubbling pool, including calculations and recalculations with MCCI codes available in Europe. Firstly, the effective heat transfer coefficients from the bulk pool to the bottom and lateral pool interfaces deduced from MCCI experiments lead to a range of a few 100 W/m2/K. By contrast, a detailed review of possible 2D convection mechanisms shows that the individual heat convection mechanisms (without taking a crust into account) such as gas bubbling convection and solutal convection overestimates the overall heat transfer coefficient, and does not account for the main trends of 2D ablation deduced from MCCI tests, which are very dependent on the composition of concrete components and aggregates. This fact, in turn, points to the effect of more complex pool/concrete interface structures. On the basis of a thorough interpretation of the experimental database and of a detailed comparison of MCCI code predictions, a set of the most realistic and consistent assumptions are identified and major remaining uncertainties are listed. © 2014 Elsevier Ltd