Browsing by Author "Ho, M"

Now showing 1 - 5 of 5
  • No Thumbnail Available
    Item
    CFD-DEM analysis of realistically heated pebble bed geometry
    (American Nuclear Society, 2019-08-18) Mardus-Hall, R; Yeoh, GH; Ho, M
    Pebble-bed, molten salt cooled reactors (PB-FHR) are a prominent reactor design and stepping stone between current generation reactors and Gen IV liquid fuelled molten salt reactor designs. They utilize spherical fuel elements as used in previous gas cooled pebble-bed reactors, while the coolant is a molten salt capable of much higher temperatures than conventional light-water reactors with the advantage of remaining at atmospheric pressure. This study implements a realistic power distribution, determined from a neutronic analysis, on to a packed bed of fuel pebbles. Utilizing coupled computational fluid dynamics (CFD) and discrete element methods (DEM) it is possible to observe the fluid and pebble flow and heat transfer characteristics in such PB-FHR systems. Previous work by the authors considered an isothermal case and a uniform power distribution across the pebble bed. The inclusion of a realistic power distribution allows for realization of accurate temperature profiles throughout the coolant fluid and fuel pebbles. The coupled nature of the method includes the pebble-pebble, pebble-fluid, and fluid-pebble exchange of momentum and energy. Current results are for a PB-FHR geometry at steady state adapted from a pebble recirculation experiment. The pebbles within the core are all assumed to be fuel pebbles, with no dummy graphite or absorber pebbles present. Analysis has demonstrated the strongly non-uniform power distribution present in the fuel pebbles in such a reactor. This non-uniformity is exacerbated at the near wall region due to the moderator effect where fuel pebbles have a marked increase in power. © 2019 The Authors.
  • No Thumbnail Available
    Item
    Energy-based approach for the evaluation of low cycle fatigue behaviour of 2.25Cr-1Mo steel at elevated temperature
    (Elsevier, 2010-08-20) Callaghan, MD; Humphries, SR; Law, M; Ho, M; Bendeich, PJ; Li, HJ; Yeung, WY
    The energy-based approach for the evaluation of low cycle fatigue behaviour of 2.25Cr–1Mo steel at elevated temperature has been investigated and detailed analyses discussed. Plastic strain energy was determined per cycle and found to characterise both crack initiation and propagation to failure regimes. At cyclic stabilisation, average plastic strain energy may be used as a suitable damage parameter and correlations between experimental and predicted data determined. The fatigue toughness to failure of the material was established and the development of a fatigue toughness to crack propagation analysis is presented. © 2010, Elsevier Ltd.
  • No Thumbnail Available
    Item
    Predictive study of condensing vapour bubble in subcooled boiling flow using intersection marker method
    (American Nuclear Society, 2019-08-18) Sharif, SA; Timchenko, V; Ho, M; Yeoh, GH
    The InterSection Marker (ISM) method, a hybrid Lagrangian-Eulerian numerical method which can model an arbitrary 3D surface within an array of cubic control-volumes, was explicitly devised to simulate multiphase phenomena, such as bubbly flows. In this work, the ISM method was used to simulate single vapour bubble condensation in a vertical rectangular channel in subcooled boiling flow condition. The vapour bubble was condensing while rising in quiescent water under the influence of the buoyancy and the surface tension forces. Coupling between the ISM interface tracking method and an in-house variable-density and variable-viscosity single-fluid flow solver was achieved by means of the immersed boundary method. In order to simulate the condensing bubble, the source terms were modelled in the CFD governing equations to account for heat and mass transfers from the bubble. During the simulation, the condensing bubble properties such as bubble history, shape, and velocity were predicted for various initial bubble sizes and liquid subcooling values. The results obtained from the ISM simulation were then compared against the past works and found to be in good agreement. The interfacial (convective) heat transfer coefficient depends on the bubble velocity. As such, bubble velocity as well as liquid subcooling play an important role in the bubble condensation rate. Bubble deforms at a higher rate for larger bubble sizes. With the increase of liquid subcooling, rise velocity of the condensing bubble decreases for continuous loss of mass (reduced buoyancy force) and for deformed bubble shape (increasing drag force). © The Authors.
  • Thumbnail Image
    Item
    A review on the development of nuclear power reactors
    (Elsevier, 2019-02) Ho, M; Obbard, EG; Burr, PA; Yeoh, GH
    Nuclear power can solve the energy trilemma of supplying baseload, clean and affordable power. However, a review of nuclear power plant (NPP) builds show mixed results, with delays in Finland and in the US offset by successes in China, South Korea and the UAE. In the West, financing for new builds has been difficult in the face of a deregulated energy market, billion-dollar upfront investments, long build times and in the case of the US historically low gas prices. We explore how the nuclear industry is innovating in facing these challenges through a review of nuclear power developments in the past, present and future. Early developments in nuclear power in the 1950s resulted in a variety of designs, out of which the pressurised water reactor (PWR) became dominant for its compactness and overall economy. Over the next 10 years, several PWR-based small modular reactor (SMR) designs are expected to come online within an eight-year timeframe. Their modular construction and fabrication in a controlled factory setting aims to shorten build times from 8 to 3 years. However, the lack of established regulatory approval pathways may be a time-limiting challenge that needs to be overcome by the first fleet of SMRs. The passive safety and a smaller fuel loading of SMRs will allow them to be deployed at more potential sites, including brownfield replacements of old coal-fired power plants or power unconventional, remote or islanded grids. Some SMRs are also designed to load follow which will allow them to work harmoniously with intermittent renewables sources with the promise of an affordable, truly carbon-neutral grid. In the longer term, advanced nuclear reactors in the form of sodium cooled, molten salt cooled, and high temperature gas cooled reactors hold the promise of providing efficient electricity production, industrial heat for heavy industry as well as the generation of hydrogen for synthetic fuel. © 2019 The Author(s). Creative Commons Published by Elsevier Ltd.
  • No Thumbnail Available
    Item
    Specimen-size dependency and modelling of energy evolution during high-temperature low-cycle fatigue of pressure vessel steel
    (Elsevier Ltd., 2011-08-01) Callaghan, MD; Humphries, SR; Law, M; Ho, M; Yan, K; Yeung, WY
    High-temperature low-cycle fatigue testing was conducted on pressure vessel steel using standard and miniature specimen sizes and the fatigue toughness required for macrocrack propagation was investigated. A definite specimen-size dependency was observed for both the threshold cumulative plastic strain energy and cycles required for macrocrack propagation, which was explained to be influenced by geometric conditions. An analytical modelling prediction was developed that accounted for specimen-size dependency and was successfully applied to predict fatigue toughness to macrocrack propagation. (C) 2011 Acta Materialia Inc.