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Tracking of bubbles using intersection marker (ISM) method
(University of Melbourne, 2016-12-05) Sharif, SA; Ho, MKM; Yeoh, GH; Timchenko, V
In this paper, one of the applications of the InterSection Marker (ISM) method is presented. The ISM method - a hybrid Lagrangian–Eulerian front-tracking algorithm specifically crafted for multi-phase flow simulation, was used to track an air bubble rising in quiescent water under the influence of buoyancy and surface tension forces. Computed bubble terminal velocity and bubble shape of 1 mm size bubble are discussed. The results compared well against the past works, and has laid foundation for the future application of the ISM method in more complex multiphase flow simulation. © The Authors.
Coupled CFD-DEM analysis of molten salt-cooled pebble-bed reactor experiment
(Americian Nuclear Association, 2017-06) Mardus-Hall, R; Ho, MKM; Yeoh, GH; Timchenko, V
The development of new nuclear reactor designs is an area of ongoing investigation, and a focus of dedicated work for various laboratories around the world. Despite the steadfast and reliable service of Light Water Reactors (LWR), the ideal power reactor, with a combination of high operational temperature, passive safety, proliferation resistance, economic build and waste minimization remains elusive. One promising design that might address these diverse, and at times contradictory requirements, is the Molten Salt Reactor (MSR). In its most radical form, a liquid fueled (LF) MSR has the nuclear fuel dissolved in the molten-salt primary coolant itself, as demonstrated by Oak Ridge National Lab (ORNL) in 1965 to 1969. An alternative fuel arrangement is to retain conventional, solid fuel elements. A proposed method is to implement pebble fuel elements, as have been used in previous gas-cooled reactors, with the gas coolant being replaced with a molten salt. This is referred to as pebble-bed, molten-salt reactor (PB-MSR). The spherical fuel pebbles used within PB-MSRs contain TRISO particles dispersed throughout the pebble’s graphite matrix. Many pebbles are constrained to form a porous bed within the core region of a reactor. Coolant molten-salt passes through the pebble bed to remove heat produced due to the nuclear fission taking place within the fuel pebbles’ TRISO particles. Various benefits are apparent with the PB-MSR design. When considering the choice of fuel elements, they are a geometry that has been produced and utilized in a similar way in the past, within gas-cooled reactors. The fuel pebbles are also able to be added to, and removed from, the core during operation, enabling on-line refueling. When considering the coolant choice, molten-salts have much higher boiling points (1703K at 1 atm. for FLiBe) than conventional coolants such as water (630K at 150 atm.), and are capable of reaching these temperatures at atmospheric pressure. This in turn removes the need for high pressure containment that is present in light water reactors and gas cooled reactors. The future implementation of new reactors, and the search for improvements in efficiency and safety in current designs, require the advancement of simulation tools, which this work ultimately aims to address.
Coupled CFD-DEM analysis of bouyant pebble bed experiment
(Americian Nuclear Association, 2017-05) Mardus-Hall, R; Timchenko, V; Yeoh, G; Ho, M
This study investigates the flow dynamics between a dense fluid and less dense solid pebbles, within a scaled experiment of a pebble bed, molten salt-cooled reactor (PB-MSR). Compared to gas-cooled pebble bed reactors there are differing flow dynamics, particularly of the pebbles themselves due to them being buoyant in the surrounding coolant, and of the fluid due to the much higher density and viscosity, combined with lower flow velocities. Utilising coupled Computational Fluid Dynamics-Discrete Element Methods (CFD-DEM), the packing structure of the pebbles, and the characteristic fluid flow structures through the packed pebble bed are investigated. The current analysis is of the pebble recirculation experiment (PREX) conducted at UC Berkeley, in which polypropylene spheres are used in conjunction with water to simulate a scaled pebble-bed reactor core’s pressure drop and packing structure. Current CFD-DEM results have shown the methods and models used within the simulation are capable of effectively describing the experimental pressure drop results of PREX, with simulation results in agreement with experimental results. The analysis extends to include the localized flow structures that are expected to be observed in flow through a packed bed experiencing spatially varying packing fractions due to wall effects. The coupled nature of the method employed includes the pebble-pebble, and pebble-fluid exchange of physical quantities for the 8,300 discrete pebbles used in the original experiment. This work will build into an effective analysis tool for PB-MSRs, and will later be expanded to incorporate heating profiles determined via neutronic modeling for heat transfer modelling of planned demonstration reactor designs such as the TMSR-SF1. © (2017) by NURETH-17
CFD-DEM analysis of heated pebble bed geometry
(Association for Iron and Steel Technology, 2018-05-18) Mardus-Hall, R; Ho, MKM; Yeoh, GH
Not available
Uranium adsorption on weathered schist – intercomparison of modelling approaches
(De Gruyter, 2004-11-01) Payne, TE; Davis, JA; Ochs, M; Olin, M; Tweed, CJ
Experimental data for uranium adsorption on a complex weathered rock were simulated by twelve modelling teams from eight countries using surface complexation (SC) models. This intercomparison was part of an international project to evaluate the present capabilities and limitations of SC models in representing sorption by geologic materials. The models were assessed in terms of their predictive ability, data requirements, number of optimised parameters, ability to simulate diverse chemical conditions and transferability to other substrates. A particular aim was to compare the generalised composite (GC) and component additivity (CA) approaches for modelling sorption by complex substrates. Both types of SC models showed a promising capability to simulate sorption data obtained across a range of chemical conditions. However, the models incorporated a wide variety of assumptions, particularly in terms of input parameters such as site densities and surface site types. Furthermore, the methods used to extrapolate the model simulations to different weathered rock samples collected at the same field site tended to be unsatisfactory. The outcome of this modelling exercise provides an overview of the present status of adsorption modelling in the context of radionuclide migration as practised in a number of countries worldwide. © 2004 Oldenbourg Wissenschaftsverlag GmbH

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