Browsing by Author "Lu, W"

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    Novel cryogenic engineering solutions for the new Australian Research Reactor OPAL
    (American Institute of Physics, 2008-03-16) Olsen, SR; Kennedy, SJ; Kim, S; Schulz, JC; Thiering, R; Gilbert, EP; Lu, W; James, M; Robinson, RA
    In August 2006 the new 20MW low enriched uranium research reactor OPAL went critical. The reactor has 3 main functions, radio pharmaceutical production, silicon irradiation and as a neutron source. Commissioning on 7 neutron scattering instruments began in December 2006. Three of these instruments (Small Angle Neutron Scattering, Reflectometer and Time-of-flight Spectrometer) utilize cold neutrons. The OPAL Cold Neutron Source, located inside the reactor, is a 20L liquid deuterium moderated source operating at 20K, 330kPa with a nominal refrigeration capacity of 5 kW and a peak flux at 4.2meV (equivalent to a wavelength of 0.4nm). The Thermosiphon and Moderator Chamber are cooled by helium gas delivered at 19.8K using the Brayton cycle. The helium is compressed by two 250kW compressors (one with a variable frequency drive to lower power consumption). A 5 Tesla BSCCO (2223) horizontal field HTS magnet will be delivered in the 2nd half of 2007 for use on all the cold neutron instruments. The magnet is cooled by a pulse tube cryocooler operating at 20K. The magnet design allows for the neutron beam to pass both axially and transverse to the field. Samples will be mounted in a 4K to 800K Gifford-McMahon (GM) cryofurnace, with the ability to apply a variable electric field in-situ. The magnet is mounted onto a tilt stage. The sample can thus be studied under a wide variety of conditions. A cryogen free 7.4 Tesla Nb-Ti vertical field LTS magnet, commissioned in 2005 will be used on neutron diffraction experiments. It is cooled by a standard GM cryocooler operating at 4.2K. The sample is mounted in a 2nd GM cryocooler (4K–300K) and a variable electric field can be applied. © 2008, American Institute of Physics
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    OPAL CNS moderator performance
    (International Group On Research Reactors, 2017-12-03) Lu, W
    Not available.
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    OPAL cold neutron source maintenance, reliability and operational status
    (International Group On Research Reactors, 2010-09-19) Taylor, D; Thiering, R; Lu, W
    Not available
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    Operational experience on the cold neutron source at the OPAL Reactor
    (European Nuclear Society, 2016-03-13) Sah, A; Walsh, P; Tobin, A; Breslin, S; Abraham, R; Lu, W
    The Cold Neutron Source (CNS) at ANSTO’s OPAL Reactor has operated with near perfect reliability since July 2013, supplying cold neutrons to neutron scattering instruments for more than 300 days a year. This recent highly productive and reliable operational period had come after a 16-month rectification program in 2012-2013 that resolved major compressor and turbine faults in the helium cryogenic system. It has been underpinned by a more focussed approach by a team of analysts, engineers and technicians, fully supported by senior management in the organisation. Drawn from the in-house knowledge base developed over the major-fault-affected years, the CNS team has been able to quickly identify the root cause of minor faults and process anomalies and carry out rectification in a timely fashion to ensure the CNS and reactor’s availability. A comprehensive Reliability Centred Maintenance (RCM) strategy has been developed, based on Failure Mode, Effects and Criticality Analysis (FMECA) methodology as part of the asset management program of the entire reactor facility. In this paper, we will share our experience with some examples of operational events. A successful project of upgrading the helium cryogenic system’s PLC in 2014 will also be discussed.
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    Rectification of the OPAL cold neutron source cryogenic system
    (International Group On Research Reactors, 2013-10-13) Lu, W
    The Cold Neutron Source (CNS) at ANSTO’s OPAL Reactor had experienced repeated outages since 2009 due to failures in the cryogenic system. An extensive root cause analysis was initiated in May 2012, led by an ANSTO team that also involved knowledgeable external experts. At the conclusion of the investigation, a set of recommendations was released to address the identified contributing causes. A rectification program was established to implement the solutions. Cryogenic operation of the CNS, providing end users with cold neutrons, successfully returned to service in July 2013. Thanks to the unique stand-by operation mode of the CNS, irradiation activities at the reactor, as well as thermal neutron availability, had not been affected during the year-long investigation/rectification process. Some technical and operational aspects of the investigation, testing and engineering modifications are discussed in this presentation.
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    Small angle and inelastic scattering investigation of nanodiamonds
    (International Conference on Neutron Scattering, 2017-07-12) Osborn, JC; Ersez, T; Lu, W
    Nanodiamond material (~5 nm diameter diamond particles) has the potential to be used in the design of the next generation of cold neutron sources (CNS). It is hoped that a blanket layer of this material surrounding the CNS moderator vessel will reflect very cold neutrons back into the moderator, thus reducing leakage through the vessel wall. In this work nanodiamonds produced by two different techniques have been studied, namely those prepared by the detonation method and by laser ablation of a carbon-hydrocarbon mixture. The analysis of experimental data from USANS, SANS and SAXS measurements performed at Australia’s OPAL reactor suggests that large scale structure such as clustering or aggregation of nanodiamond particles may be determining the scattering. The generalised density of states (GDOS) obtained at 20 K from TOF inelastic neutron scattering measurements showed no low energy states. The GDOS of heated and unheated samples at 300 K are consistent with the proposition that thermal treatment of nanodiamond samples eliminates hydrogen in the form of water absorbed on the nanoparticle surface. Hydrogen bonded to carbon is difficult to remove by thermal treatment.
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    Structure evolution of nanodiamond aggregates: a SANS and USANS study
    (International Union of Crystallography, 2022-02-21) Kabir, II; Osborne, JC; Lu, W; Mata, JP; Rehm, C; Yeoh, GH; Erez, T
    Ultra-small-angle neutron scattering (USANS) and small-angle neutron scattering (SANS) measurements, covering length scales from micrometres to nanometres, were made to investigate the structure of nanodiamonds (NDs) and their suspensions. These nanodiamonds were produced by two different techniques, namely by the detonation method and by the laser ablation of a carbon-hydrocarbon mixture. The (U)SANS results indicated the presence of structures four orders of magnitude larger than the dimensions of a single ND particle, consisting of aggregations of ND particles. This aggregation of the ND particles was studied by employing the contrast variation technique. Two different solvents, namely H2O and dimethyl sulfoxide (and their deuterated counterparts), were used to understand the role of hydrogen in the shape and size of the aggregates. The analysis of experimental data from SANS measurements also reveals the ND particles to have an ellipsoidal structure. Using a defined shape model and the SANS contrast variation technique, it was possible to characterize the non-diamond outer shell of the particles and determine the outer layer thickness. This clarification of the structure of the NDs will allow better preparation of suspensions/samples for various applications. Understanding the structure of NDs at multiple length scales also provides crucial knowledge of particle-particle interaction and its effect on the aggregation structures. © International Union of Crystallography - Open Access CC BY licence.