Browsing by Author "Wong, L"

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    Benchmark consolidated results against experimental data from SPERT IV statics
    (International Atomic Energy Agency, 2019-08) Day, SE; Braoudakis, G; Wong, L
    The IAEA CRP (CRP 1496) on ‘Benchmarking, against Experimental Data, of the Neutronic and Thermalhydraulic Computational Methods and Tools for Operation and Safety Analysis for Research Reactors’ provides a unique opportunity to benchmark and compare the accuracy and efficiency of both off-the-shelf and locally developed computational tools to a wide set of experimental research reactor benchmark analysis. In the scope of this project, various analysis groups have evaluated the SPERT IV benchmark analysis – consisting of a variety of commissioning experiments and multiple sets of Reactivity Insertion Accident (RIA) measurements. This report is focused on the commissioning experiments and associated measurements, referred to herein as the ‘Statics’ or neutronic section of the SPERT IV benchmark analysis. It summarizes and compares the analysis methodologies adopted, the code systems employed, and the simulation results generated by the various analysis groups. A comparison of the computational results to available experimental results is also provided in this report. © 2019 The Authors
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    High resolution synchrotron XPS study of L-cysteine and S-benzyl-L-cysteine on platinum: adhesion mechanisms and radiation damage
    (Australian Institute of Physics, 2006-12-07) Wong, L; Yayebjee, M; Stampfl, APJ; Chen, CH; Wang, SC; Huang, ML; Klauser, R
    Key to the development of functional biomaterials and innovative technologies behind medical implants and biosensors is a deep understanding of the interaction between inorganic surfaces and biological systems at the molecular level. Amino acids adhered onto inorganic substrates are model systems which may be analysed at a fundamental level using x-ray photoelectron spectroscopy (XPS) [1]. L-cysteine has been proposed as a potential anchor for larger molecules, e.g. proteins, to adhere onto metals such as Au, due to cysteine’s reactive thiol group [2]. This paper presents a related but unexplored system: in-situ prepared L-cysteine on Pt{111}. Pt{111} is an atomically flat surface and is a relevant material, used in biosensors and medical implants. To compare the adhesion characteristics of small and large molecules, S-benzyl-L-cysteine on Pt{111} is also analysed. Core level binding energies are examined using high resolution XPS at the National Synchrotron Radiation Research Centre (NSRRC) in Taiwan. Analysis of S 2p binding energies indicates cysteine adsorption via the thiol group. Two N 1s peaks in the spectra suggest that cysteine is present in both neutral and zwitterionic forms. Analysis of S-Benzyl-L-Cysteine core level shifts demonstrates similar adhesion characteristics. An important consideration in the application of biosurfaces is the impact of x-ray irradiation. XPS, using an excitation energy of 480eV, is used to examine the damage to each surface, due to exposure from the x-ray beam. The dramatic evolution of the N 1s spectra from both molecules suggests cleavage of the amine group. In addition, C 1s spectra from L-cysteine and S-benzyl-L-cysteine show cleavage of the carboxyl group due to prolonged irradiation. [1] B. Kasemo, Surf. Sci., 500, 2002, 656. [2] O.Cavalleri, L. Oliveri, A. Daccà, R. Parodi and R. Rolandi, App. Surf. Sci., 175, 2001, 357
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    A medium-energy photoemission and ab-initio investigation of cubic yttria-stabilised zirconia
    (AIP Scitation, 2014-03-01) Cousland, GP; Cui, XY; Smith, AE; Stampfl, CM; Wong, L; Tayebjee, M; Yu, DH; Triani, G; Evans, PJ; Ruppender, HJ; Jang, LY; Stampfl, APJ
    Experimental and theoretical investigations into the electronic properties and structure of cubic yttria-stabilized zirconia are presented. Medium-energy x-ray photoemission spectroscopy measurements have been carried out for material with a concentration of 8-9 mol. % yttria. Resonant photoemission spectra are obtained for a range of photon energies that traverse the L2 absorption edge for both zirconium and yttrium. Through correlation with results from density-functional theory (DFT) calculations, based on structural models proposed in the literature, we assign photoemission peaks appearing in the spectra to core lines and Auger transitions. An analysis of the core level features enables the identification of shifts in the core level energies due to different local chemical environments of the constituent atoms. In general, each core line feature can be decomposed into three contributions, with associated energy shifts. Their identification with results of DFT calculations carried out for proposed atomic structures, lends support to these structural models. The experimental results indicate a multi-atom resonant photoemission effect between nearest-neighbour oxygen and yttrium atoms. Near-edge x-ray absorption fine structure spectra for zirconium and yttrium are also presented, which correlate well with calculated Zr- and Y-4d electron partial density-of-states and with Auger electron peak area versus photon energy curve. © 2014, AIP Publishing LLC.
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    Neutronics core optimisation of the Jules Horowitz Reactor
    (European Nuclear Society, 2012-03-18) Wong, L; Pouchin, B
    The Jules Horowitz Reactor (JHR) is a materials testing reactor currently under construction at the Cadarache site of the Commissariat a l‘Energie Atomique et aux Energies Alternatives (CEA). Within the reactor core, it is envisaged that experimental devices will be placed within the vacant positions in the core rack for irradiation under fast flux. Thus, the current configuration of the core has been optimised for a hard neutron spectrum. However, depending on the experimental device loading in the core, this fast flux optimisation in the core may not be necessary. Instead, in this situation, it is more economical to thermalise the flux and increase the cycle duration. A neutronics study using TRIPOLI-4 was performed to locate positions within the JHR core in which neutron moderating materials, beryllium or water, could be placed, in order to increase the reactivity in the core. These positions include the experimental device positions at the centre of the fuel assembly, and interassembly or outer periphery positions which are currently designated to be filled by aluminium cylinders. The impact of these materials on the experimental device performance within the core and in the reflector and the flux distribution within the core was analysed. Operating cycle gains of several full power days were identified.
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    Preliminary thermohydraulics design of LORELEI an experimental device of JHR
    (European Nuclear Society, 2012-03-18) Nitti, FS; Bourdon, S; Gonnier, C; Roux, P; Estrade, J; Bignan, G; Wong, L
    ln the Jules Horowitz Reactor (JHR) experimental facilities will be available, including the Light water One Rod Equipment for LOCA Experimental Investigations (LORELEI) device. ln this work the thermohydraulics design of the LORELEI facility was developed with the code CATHARE-2. The objective of the work was: to define a 3D geometry of the facility and to verify the capacity of the system, under natural circulation, to remove the power generated both by the fuel rod (up to 400 W/cm) and by gamma irradiation heating on the structures, during the re-irradiation phase before the simulation of the high temperature transient. A parametric calculation modifying several geometrical parameters was performed. The parameters that should be varied were evaluate with an analytical approach. A final geometry of the facility, able to work in natural circulation condition up to the maximum power was selected. Further calculation was performed to analyze the correlation between the accumulation of steam and the geometries of device at constant power.
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    Single crystal neutron diffraction on the clathrates of Sr8Ga16Ge30, Ba8Ga16Ge30 and Sr4Ba4Ga16Ge30
    (Australian Institute of Physics, 2006-12-05) Tayebjee, M; Piltz, RO; Yu, DH; Cai, K; Wong, L; Stampfl, APJ
    The key consideration in the development of more efficient thermoelectric materials is to design materials that conduct heat like a glass but maintain good crystal-like electrical conductivities, that is to design so called “phonon glass and electron crystals (PGEC’s), as proposed by Slack [1]. One potential PGEC are clathrates that consist of a cage framework of the group 13/14 elements and alkali, alkaline earth or rare earth atoms trapped within the cages. The properties of such clathrates strongly depend on the details of their structures, the dynamic disorder of the trapped atoms as well as the distribution of framework atoms. The structure of single crystals of Sr8Ga16Ge30, Ba8Ga16Ge30 and Sr4Ba4Ga16Ge30 are characterized by single crystal neutron diffraction. The general gallium-doped germanium cage structure with strontium or barium guest atoms inside is confirmed. The lattice constants are 10.704(1)Å, 10.759(2)Å and 10.757(2)Å for Sr8Ga16Ge30, Ba8Ga16Ge30 and Sr4Ba4Ga16Ge30 respectively. Each unit cell contains two 20-atom cages and six 24-atom cages containing strontium/barium atoms. Analysis of the Sr8Ga16Ge30 cage structure shows that gallium atoms preferentially occupied the 6c site and avoided the 16i site. At the 6d site in the 24-atom cage, large atomic displacement parameters (ADP) from guest-atoms are determined for all structures. Further experiment at low temperature is in progress. [1] G. A. Slack, in CRC Handbook of Thermoelectrics, Edited by D. M. Rowe (CRC Boca Raton, FL, 1995), pp 407-440
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    The structure of yttria-stabilised zirconia: a combined medium energy photoemission and ab-initio investigation
    (Australian Institute of Physics, 2011-02-01) Cousland, GP; Wong, L; Tayebjee, M; Yu, DH; Triani, G; Stampfl, APJ; Cui, X; Stampfl, CM; Smith, AE
    Cubic zirconia-based materials are candidates for use in the nuclear fuel cycle. There are three phases of ZrO2, a room temperature monoclinic phase and higher temperature tetragonal and cubic phases. The cubic phase of zirconia, in comparison to the other phases, exhibits a very low thermal conductivity, allowing the material to be potentially used in high temperature fission and fusion environments. Interestingly, the cubic-phase may be stabilised at room temperature through the addition of small quantities of other oxides for example, Y2O3, CaO and Ce2O3. Recent ab initio calculations for yttria-stablised zirconia (YSZ) predict the atomic geometry for various oxygen-vacancy containing structures [1]. In particular, a set of “rules” is used to establish a structure for 6.25 Mol % [1,2]. This model is extended to a yttria content of 9.375 Mol % and compared with a sample of 9.5 Mol % yttria. Using this model, core-level shifts are estimated as changes in binding energy obtained from density-functional theory (DFT) calculations, due to the different chemical environments. The partial density-of-states of Y atoms differ depending upon whether there are oxygen vacancies at nearest-neighbour sites to the Zr atoms. Experimentally, a number of different core-levels and Auger-lines are acquired across the L-edges of Zr and Y. By measuring through the Y Ledge resonance, three distinct Zr environments and three distinct oxygen environments are observed in photoelectron peaks. The area under each peak is plotted against photon energy.