Journal: Nuclear Engineering and Technology

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Elsevier

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ISSN

1738-5733

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2016 - 201912020 - 20263
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Publications 1 - 4 of 4
  • An explicit approximation of the central angle for the curved interface in double-circle model for horizontal two-phase stratified flow
    Item type: Journal Article
    Ahn, Taehwan; Jeong, Dongwon; Bak, Jin-Yeong; et al. (2024)
    Nuclear Engineering and Technology
    Stratified flow in horizontal tubes is frequently observed in gas-liquid two-phase flow system. In the two-fluid modeling, it is important to define the interface shape in solving the balance equations to determine the key parameters such as the interfacial transfer terms, void fraction, and pressure drop. A double-circle model is usually introduced to depict the concave-down interface in a horizontal circular tube under the stratified-wavy flow condition. However, calculation of the central angle in the double-circle model, which represents the interfacial curvature, requires an appropriate iterative numerical root-finding scheme to solve the implicit transcendental equation. In this study, an explicit approximate equation has been proposed without requirement of the iterative scheme and numerical instability, which is expected to improve the coding process and computation efficiency in the analysis code with the two-fluid model.
  • Study of a thick CRUD on irradiated fuel rod: correlating thermodynamic calculations and X-ray characterizations
    Item type: Review Article
    Nichenko , Sergii; Schneider , Cloé; Grażyna Makowska , Małgorzata; et al. (2026)
    Nuclear Engineering and Technology
    A significantly elevated layer of so-called CRUD (corrosion deposit) was observed on the surface of a boiling water reactor irradiated fuel rod, potentially leading to hot spots and subsequent cladding rupture. To study this phenomenon, comprehensive investigations were conducted employing two complementary approaches: computer-aided chemical thermodynamic calculations and experimental characterizations. Micro-beam X-ray diffraction (XRD) combined with X-ray fluorescence (XRF) at the Swiss Light Source (SLS) facilitated the identification and localization of phases. Notably, the distinctive presence of Si-rich phases (Zn₂SiO₄ as the main phase and SiO₂ as a minor component) was observed in the thick CRUD sample, while absent in the reference sample. Furthermore, thermodynamic calculations were conducted to simulate CRUD formation at prototypical conditions and scenarios, supplementing the experimental results. These simulations demonstrated that under typical oxidizing conditions, Zn₂SiO₄, Fe₂O₃, ZnO and Zn-ferrites are the predominant phases formed, which is consistent with experimental observations. The synergy between simulations and experimental data improves our understanding of CRUD formation mechanisms and CRUD composition and highlights the predictive capacity of thermodynamic simulations in studying the intricate corrosion phenomena.
  • Bubbly, Slug, and Annular Two-Phase Flow in Tight-Lattice Subchannels
    Item type: Journal Article
    Prasser, Horst-Michael; Bolesch, Christian; Cramer, Kerstin; et al. (2016)
    Nuclear Engineering and Technology
    An overview is given on the work of the Laboratory of Nuclear Energy Systems at ETH, Zurich (ETHZ) and of the Laboratory of Thermal Hydraulics at Paul Scherrer Institute (PSI), Switzerland on tight-lattice bundles. Two-phase flow in subchannels of a tight triangular lattice was studied experimentally and by computational fluid dynamics simulations. Two adiabatic facilities were used: (1) a vertical channel modeling a pair of neighboring subchannels; and (2) an arrangement of four subchannels with one subchannel in the center. The first geometry was equipped with two electrical film sensors placed on opposing rod surfaces forming the subchannel gap. They recorded 2D liquid film thickness distributions on a domain of 16 x 64 measuring points each, with a time resolution of 10 kHz. In the bubbly and slug flow regime, information on the bubble size, shape, and velocity and the residual liquid film thickness underneath the bubbles were obtained. The second channel was investigated using cold neutron tomography, which allowed the measurement of average liquid film profiles showing the effect of spacer grids with vanes. The results were reproduced by large eddy simulation þ volume of fluid. In the outlook, a novel nonadiabatic subchannel experiment is introduced that can be driven to steady-state dryout. A refrigerant is heated by a heavy water circuit, which allows the application of cold neutron tomography.
  • Experimental investigation on bubble behaviors in a water pool using the venturi scrubbing nozzle
    Item type: Journal Article
    Choi, Yu Jung; Kam, Dong Hoon; Papadopoulos, Petros; et al. (2021)
    Nuclear Engineering and Technology
    The containment filtered venting system (CFVS) filters the atmosphere of the containment building and discharges a part of it to the outside environment to prevent containment overpressure during severe accidents. The Korean CFVS has a tank that filters fission products from the containment atmosphere by pool scrubbing, which is the primary decontamination process; however, prediction of its performance has been done based on researches conducted under mild conditions than those of severe accidents. Bubble behavior in a pool is a key parameter of pool scrubbing. Therefore, the bubble behavior in the pool was analyzed under various injection flow rates observed at the venturi nozzles used in the Korean CFVS using a wire-mesh sensor. Based on the experimental results, void fraction model was modified using the existing correlation, and a new bubble size prediction model was developed. The modified void fraction model agreed well with the obtained experimental data. However, the newly developed bubble size prediction model showed different results to those established in previous studies because the venturi nozzle diameter considered in this study was larger than those in previous studies. Therefore, this is the first model that reflects actual design of a venturi scrubbing nozzle.
Publications 1 - 4 of 4