Browsing by Author "Mokhber-Shahin, L"
Now showing 1 - 19 of 19
Results Per Page
Sort Options
- ItemAnalysis of hot particle characteristics affecting environmental fate and interaction with living organisms(SPERA, 2016-09-09) Johansen, MP; Child, DP; Collins, RN; Hotchkis, MAC; Howell, NR; Payne, TE; Ikeda-Ohno, A; Mokhber-Shahin, LThe 2nd International Conference on the Sources, Effects and Risks of Ionizing Radiation (SERIR-2) and the 14th Biennial Conference of the South Pacific Environmental Radioactivity Association (SPERA-2016) and will be held in Bali, Indonesia 5-9 September 2016. The South Pacific Environmental Radioactivity Association (SPERA), in conjunction with the Indonesian National Nuclear Energy Agency (BATAN) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) made the decision to jointly hold these conferences in one week at the same venue to avoid topical overlap and to strengthen regional participation at both events. SERIR2 will be a 1-day conference (5 September) and deals with the efforts to enhance data collection and disseminate scientific findings related to the issues of sources, effects and risks of the ionizing radiation, as well as to seek ways of communicating with stakeholders (scientific communities, regulatory authorities and general public) on those issues. The 14th Biennial Conference of the South Pacific Environmental Radioactivity Association (SPERA), to be held 6-9 September, provides a platform for discussion and debate among scientists on the occurrence, behaviour, impact and measurement of radioactive species present in the environment through natural processes, or resulting from human activities. This international conference facilitates knowledge sharing on environmental radioactivity and related topics of local and global significance. The joint conference will be held 5-9 September 2016, with a welcome reception on 4 September, at the Sanur Paradise Plaza Hotel in Bali. The joint conference will include a one-day workshop on the 6 September on topic(s) to be decided.
- ItemCapability development for the quantification of Ba-133 in milk powder by gamma-ray spectrometry(South Pacific Environmental Radioactivity Association, 2018-11-06) Van De Voorde, R; Mokhber-Shahin, L; Harrison, JJ; van Wyngaardt, WM; Jackson, TWBarium-133 (Ba-133) is a fission product with a half-life of 10.5 years. It decays to its daughter radionuclide Cs-183 by electron capture, emitting multiple characteristic gamma emissions. The capability to accurately quantify Ba-133 is of importance due to its persistence in the environment. This is enabled by its relatively long half-life and its uptake into the food chain due to its similarity in chemical properties to calcium. Therefore, screening for contamination of calcium-rich foodstuffs such as milk and milk powders, is required following a nuclear or radioactive contamination event. Refining a capability to quantify Ba-138 utilising gamma-ray spectrometry is advantageous due to its requirement of minimal sample preparation and usefulness in screening for a wide range of other radionuclides, therefore providing critical information in a relatively timely manner. in the 2017 IAEA ALMERA proficiency test exercise ANSTO’s Radioanalytical Chemistry Capability group demonstrated its proficiency in quantifying Ba-138 in water, and in quantifying other nuclides such as Cs-187 and Sr-90 in milk powder. However, the activity concentration of Ba-188 in the milk powder matrix was lower than the target value. Therefore, a study was undertaken to optimise a method for accurately quantifying Ba-138 in milk powder by gamma-ray spectrometry, holistically investigating the entire process from sample receipt and storage to counting geometry and interpretation of data. A series of storage and drying experiments were undertaken to optimise a method for determining the moisture content of a variety of supermarket bought milk powders, comparing measured mass changes using both desiccator and benchtop cooling following oven-drying. The impact of storage following unsealing the received sample container on moisture content was investigated and its implications on subsequent internal and cross-laboratory analysis were explored. The milk powders were packed into various geometries and analysed by gamma-ray spectrometry to quantify the naturally-occurring radionuclides present in the milk powder. This data was used to better understand the matrix and investigate the possible interference of naturally-occurring radionuclides in the quantification of Ba-188. Milk powders were also purposefully spiked with known activities of Ba-133 and a comparison of various counting geometries, the impact of sample density and self-absorption on counting efficiency were investigated. The use of a variety of calibration standards of varying geometries and densities was also explored to assess their applicability to the milk powder matrix. This paper will detail the investigation findings and propose recommendations for a more reliable method for the quantification of Ba-133 in milk powder by gamma-ray spectrometry to be hence employed in ANSTO’s Radioanalytical Chemistry Capability laboratory.
- ItemComparison of Be-7 analysis using two gamma spectrometry systems and software packages(South Pacific Radioactivity Association, 2008-11-26) Zawadzki, A; Mokhber-Shahin, L; Fierro, D; Shamnugarajah, K; Ciufici, JNaturally occurring radioisotope, Be-7, can be used to study short term deposition and resuspension cycle of surficial bed sediments. The activity of Be-7 can be determined by gamma spectrometry. Due to Be-7 short half life, samples must be analysed within a few days of collection on several gamma spectrometry systems. To test the precision of Be-7 data from two gamma spectrometry systems and software packages, multiple analysis of a sediment sample was performed over 6 months. A statistical procedure was used to investigate the precision of the analytical data as the activity of Be-7 decreases over time. The sample was prepared from a sediment sample spiked with Be-7 activity, collected from fresh rain water, and counted on High Purity Germanium (HPGe) gamma spectrometry systems from EG&G Ortec and Canberra. Software packages Gamma Vision and Genie-PC were employed to determine peak areas and activity calculations. Calculations were also performed manually by visual determination of the Be-7 peak region of interest and simple gamma spectrometry calculation procedure.
- ItemComparison of radium-228 determination in water among Australian laboratories(Elsevier, 2017-11) Zawadzki, A; Cook, M; Cutmore, B; Evans, F; Fierro, D; Gedz, A; Harrison, JJ; Loosz, T; Medley, P; Mokhber-Shahin, L; Mullins, S; Sdraulig, SThe National Health and Medical Research Council and Natural Resource Management Ministerial Council of Australia developed the current Australian Drinking Water Guidelines which recommend an annual radiation dose value of 1 mSv year−1. One of the potential major contributors to the radiation dose from drinking water is radium-228, a naturally occurring radionuclide arising from the thorium decay series. Various methods of analysing for radium-228 in water have been established and adapted by analytical radiochemistry laboratories. Seven laboratories in Australia participated in analysing radium-228 spiked water samples with activity concentrations ranging from 6 mBq L−1 to 20 Bq L−1. The aim of the exercise was to compare and evaluate radium-228 results reported by the participating laboratories, the methods used and the detection limits. This paper presents the outcome of the exercise. Crown Copyright © 2017 Published by Elsevier Ltd.
- ItemEnvironmental and effluent monitoring at ANSTO sites, 1999(Australian Nuclear Science and Technology Organisation, 2000) Hoffmann, EL; Loosz, T; Mokhber-Shahin, LResults are presented of environmental and effluent monitoring conducted in 1999 at the two sites owned and operated by ANSTO at the Lucas Heights Science and Technology Centre (LHSTC) and the National Medical Cyclotron (NMC). All low-level liquid and gaseous effluent discharges complied with existing discharge authorisations and relevant environmental regulations. Potential effective doses to the general public from LHSTC controlled airborne discharges were estimated for 1999 using the PC-Cream atmospheric dispersion and dosimetry code. The potential effective doses to the public in 1999 were estimated to be less than 0.010 mSv/year for all receptor locations on the LHSTC 1.6 km buffer zone boundary or beyond. This value represents 1% of the I milli sievert (mSv) per year dose limit for long term exposure that is recommended by the National Health and Medical Research Council and 3.3% of the LHSTC site dose constraint of 0.3 mSv/year. It is concluded that there is no impact on the health of the community staff or the environment as a consequence of operations at the Lucas Heights Science and Technology Centre or the National Medical Cyclotron.
- ItemEnvironmental and effluent monitoring at ANSTO sites, 2000(Australian Nuclear Science and Technology Organisation, 2001) Hoffmann, EL; Loosz, T; Mokhber-Shahin, LResults are presented of environmental surveillance and effluent monitoring conducted in the calendar year 2000 at the two sites owned and operated by ANSTO at the Lucas Heights Science and Technology Centre (LHSTC) and the National Medical Cyclotron (NMC). All low-level liquid and gaseous effluent discharges complied with existing discharge authorisations and relevant environmental regulations. Potential effective doses to the general public from LHSTC controlled airborne discharges were estimated for 2000 using the PC-Cream atmospheric dispersion and dosimetry code. The potential effective doses to the public in 2000 were estimated to be less than 0.01 mSv/year for all receptor locations on the LHSTC 1.6 km buffer zone boundary or beyond. This value represents 1 % of the 1 milli sievert (mSv) per year dose limit for long term exposure that is recommended by the National Health and Medical Research Council and 3.3% of the LHSTC site dose constraint of 0.3 mSv/year. It is concluded that there is no impact on the health of the community staff or the environment as a consequence of operations at the Lucas Heights Science and Technology Centre or the National Medical Cyclotron.
- ItemEnvironmental and effluent monitoring at Lucas Heights Science and Technology Centre, 1998(Australian Nuclear Science and Technology Organisation, 1998) Hoffmann, EL; Loosz, T; Farrar, Y; Mokhber-Shahin, LResults are presented of environmental and effluent monitoring conducted in the vicinity of the Lucas Heights Science and Technology Centre (LHSTC) during 1998. All low-level liquid and gaseous effluent discharges complied with existing discharge authorizations and relevant environmental regulations. Potential effective doses to the general public from controlled airborne discharges from HIFAR were estimated utilising the PC-Cream atmospheric dispersion and dosimetry code. The potential effective dose to the public was estimated to be less than 0.010 mSv/year for all receptor locations on the 1.6 km buffer zone boundary around the HIFAR research reactor. This value represents 1% of the 1 mSv/year dose limit for long term exposure that is recommended by the National Health and Medical Research Council and 3.3% of the site dose constraint of 0.3 mSv/year approved by the Nuclear Safety Bureau. It is concluded that there is no impact on the health of the community staff or the environment as a consequence of operations at the LHSTC.
- ItemEstablishing a radioanalytical capability to support cyclotron decomissioning(South Pacific Environmental Radioactivity Association, 2022-11-20) Thiruvoth, S; Harrison, JJ; Bedwell-Wilson, J; Cunynghame, T; Martiniello, J; Mokhber-Shahin, L; Silitonga, AThe 30 MeV cyclotron at the National Medical Cyclotron (NMC) ceased operations in October 2009 after producing medical isotopes for application in nuclear medicine for approximately 20 years. Upon its closure a process of decommissioning commenced. Initially, internal components that make up the cyclotron were removed, leaving behind the vault. The vault is predominantly constructed of concrete and steel reinforcements. Neutron activation of these materials produced radioisotopes that will need to be accurately identified and quantified to support decision making around storage and disposal options of these materials. This is a critical aspect of any cyclotron decommissioning project and has safety, environmental and economic implications. A capability to quantify typical radionuclides found in cyclotron materials is being developed at ANSTO. Cyclotron vault materials that may require assessment are concrete, steel and waters. Radionuclides of interest are typically beta- and gamma-emitting neutron activation products. Non-destructive, high resolution gamma spectrometry will be applied to quantify gamma emitting radionuclides such as 152Eu, 154Eu, 134Cs and 60Co. The complex matrix of some reactor materials will cause attenuation of gamma photons and empirical and/or theoretical corrections will be applied. Beta-emitting radionuclides will require a suite of destructive radioanalytical techniques designed to isolate and quantify beta-emitting radionuclides such as 59Fe and 55Fe. Gross beta counting will assist in identifying which samples will require destructive beta analysis. This presentation will outline the approach taken in identifying a sampling strategy and in the method development for non-destructive and destructive analysis and how this can support future cyclotron decommissioning needs of Australia and our region.
- ItemEstablishing a radioanalytical capability to support reactor decommissioning(South Pacific Environmental Radioactivity Association, 2018-11-06) Harrison, JJ; Martiniello, J; Mokhber-Shahin, L; Rowling, B; Silitonga, AS; Thiruvoth, S; Vardenega, C; Van De Voorde, R; Wilsher, KL; Wong, HKYAustralia’s first reactor, the 1O megawatt High Flux Australian Reactor (HIFAR) vi/as operated between 1958 and 2007. HIFAR was one of six DIDO reactors which were installed in the UK, Denmark, Germany and Australia. HIFAR was a multi-purpose reactor, initially used for nuclear material research followed by production of medical radioisotope; an: neutron diffraction experiments. Atter HIFAR was closed, a process of decommissioning commenced. Initially, internal components such as the fuel and heavy water (which acted as primary coolant and neutron moderator) were removed. Currently, HIFAR is in a “care and maintenance" phase whereby short-lived radionuclides can decay and non-radioactive equipment and instrumentation removed. Approximately 1OO research and power reactors have been decommissioned around the world including two of the DIDO class reactors at Harwell, UK and Risø, Denmark. ANSTO can draw on international experience as we as well as experience gained during decommissioning of its own 100 kilowatt Moata reactor in 2010. Accurate identification and quantification of radioactivity is a critical safety, environmental and economic aspect of any nuclear reactor decommissioning project as it supports decision making around long-term storage of disposal options of reactor materials as well as environmental assessment of the reactor site. A capability to quantify typical radionuclides found in reactor materials and environmental samples is being developed at ANSTO. Reactor materials that may require assessment include concrete, graphite and steel and environmental samples include soils and waters. Radionuclides of interest are predominantly beta- and gamma-emitting fission and activation products. Non—destructive, high resolution gamma spectrometry will be applied to quantify gamma emitting radionuclides such as 60Co, 66Zn, 133 Ba, 137Cs, 152 Eu, and 154Eu. The complex matrix of some reactor materials will cause attenuation of gamma photons and empirical and/or theoretical corrections will be applied. Beta-emitting radionuclides with weak or no gamma emission lines cannot be easily identified or quantified in solid materials using non-destructive techniques. This is due to attenuation of the beta particles, the nature of the beta emission spectrum and interferences from other beta- and gamma-emitting radionuclides. A suite of destructive radioanalytical techniques, designed to isolate and quantify beta-emitting radionuclides such as 3H, 14C, 36CI, 55Fe, 63Ni, 98Sr and 99Tc is being developed. This paper will present the timeline for development and the progress to date of this radioanalytical capability which will support the current and future decommissioning needs of Australia and our region.
- ItemEstimating diffusion in heterogeneous groundwater systems using short-llived radio-isotopes and stable isotopes or bromine(Geological Society of Australia, 2014-07-07) Peterson, MA; Cendón, DI; Andersen, MS; Mokhber-Shahin, L; Wong, HKY; Rowling, BDiffusion is an important and ubiquitous phenomenon in nature, but too often neglected or unmeasured in water resource hydrogeology or solute transport. Diffusion may, in fact, be the dominant process that dictates hydrogeochemistry and affects tracers. Conservative and age tracers are commonly used for water resource or contaminant plume transport estimations, but will give misleading results, if diffusion is ignored. Diffusion of tracers into aquitards, matrix pores of fractured rocks, blind fractures or other low conductivity zones lead to retardation and possible adsorption, exchange, precipitation or decay. This becomes increasingly important as heterogeneity of flow domains increase, for example, in fractured rock aquifers, interlayered sediments or aquifers associated with aquitards. Traditional methods of measuring diffusion coefficients in small slices of heterogeneous rock are unreliable for upscaling, so this study presents an alternative method based on lab-scale drill-core tests and suggests field-scale borehole tracer tests. Fick’s first law shows that diffusion rates are driven by concentration gradients. Short-lived radiotracers soon reach a steady-state concentration gradient with enhanced flux where diffusion rate equals decay, while stable tracers trend towards saturation and ever-decreasing fluxes. We compare diffusion of short-lived radiotracers 131I half-life 8 days) or 82Br (half-life 1.5 days) to their stable equivalent (I or Br) into 45–50 cm lengths of ~60 mm diameter drill core. Five cores were selected from three fractured rock environments: sandstone, limestone and metavolcanics. By regularly sampling and refilling the annulus with tracers around the enclosed core, we are able to discern differential in-diffusion between stable- and radio-tracers. For example, the annulus was sampled and refilled weekly with an (equivalent decayed) 131I activity of 22 Bq/g and within three weeks (2.6 half-lives) each core had reached a characteristic steady state flux. The net fluxes were 7 around 1.0 Bq/cm2/week in the sandstone cores, 0.2 Bq/cm2/week in the metavolcanics, and 0.05 Bq/cm2/week in the limestone. This was compared to stable iodine weekly refills at 2.6 mg/L, which gave ever-diminishing diffusion results. The net fluxes of stable iodine diminished steadily, e.g. over three weeks from 98 to 26 ng/cm2/week for the most porous (medium sandstone ~15%), and from 11 to 7 ng/cm2/week for the least porous (limestone ~2%). Experiments were also performed using 82Br and stable bromine, with sampling and refills performed on a daily (0.68 half-lives) basis. Similar trends were apparent, though the data was noisier due to more frequent refills and less time for diffusion to generate significant changes in the annulus reservoir solutions. This method enables analysis of drill cores for comparative effective diffusion coefficients of different systems. Quantitative interpretation is currently being refined. In principle, the method should be transferrable to single boreholes or tracer tests between multiple boreholes to gain larger scale representation of effective diffusion within a groundwater system. The normally confounding factors, such as dilution, advection, exchange, adsorption and precipitation, are negated by comparing the stable with radio-tracer results, as all isotopes of these elements are identically affected by such processes and losses. © Geological Society of Australia Inc
- ItemMethods for isolating plutonium particles in Maralainga soils(Australian Nuclear Science and Technology Organisation, 2012-10-16) Mokhber-Shahin, L; Johansen, MP; Collins, RN; Payne, TEA combination of density-separation and gamma testing methods was used to isolate a plutonium (Pu)-containing particle from the host Maralinga soils. Such separation is necessary in order to reduce or eliminate interference from other elements in the host soils that may occur during analysis methods (e.g., synchrotron XANES) used for determining physico-chemical information such as compound speciation and oxidation state. Soil samples were obtained from the Taranaki test area, at Maralinga, South Australia, where Pu had been dispersed by high explosive detonation and through burning in the 1950s. Bulk soil samples were first screened using HPGe gamma-ray spectrometer for detection of Am-241 (0.060 MeV gamma emission) which co-exists with the Pu in the dispersed particles at a concentration ratio of approximately 1:7.5 (Am-241 to Pu-239). The sample was sieved (125 μm) to remove large sand particles and debris. Density separation was accomplished by repeated sonification (0.5 in. probe tip sonifier) and centrifugation of mixtures of soil and lithium heteropolytungstate (density of 2.9 g/ml). The various density fractions were tested for Am-241 through gamma counting. This process was repeated until a small mass (<0.01 g) of heavy particles remained. Further isolation was accomplished using microscope, physical separation, and gamma counting. The result of the process was isolation of a small particle, containing Am and Pu isotopes that had been originally part of a non-critical nuclear weapons test. The particle had been dispersed approximately two kilometres through the air pathway, and has been subjected to +60 years of weathering and chemical interaction processes. The isolation process allows for further testing of the Pu, without interference from natural soil elements, to provide a range of pathway, biological uptake, and dose information.
- ItemPlutonium uptake in wildlife at Maralinga, South Australia(Australian Nuclear Science and Technology Organisation, 2012-10-16) Johansen, MP; Child, DP; Collins, RN; Davis, E; Doering, C; Harrison, JJ; Hotchkis, MAC; Payne, TE; Mokhber-Shahin, L; Ryan, B; Thiruvoth, S; Twining, JR; Wilsher, KL; Wood, MDThis study examined accumulation of plutonium (Pu) in wildlife at Maralinga, South Australia, where a 1950s series of experiments dispersed unfissioned Pu onto the landscape. The residual Pu concentrations that remain today are lower than the site clean-up level, but are sufficient to provide a rare opportunity to study wildlife organisms that have been exposed to a food web and soils containing elevated Pu. Analysis was by gamma- and alpha- spectroscopy, and by accelerator mass spectrometry at ANSTO. Uptake of Pu was quantified by concentration ratios, defined as average concentration in the whole-organism, to that of their host soil (CRwo-soil). The geometric mean of CRwo-soil values for all organisms was 0.002 (geometric standard deviation – 4.1E00) with mammals
- ItemPreparation of certified reference materials for gross alpha beta measurement(South Pacific Environmental Radioactivity Association, 2018-11-06) Wilsher, KL; Harrison, JJ; van Wyngaardt, WM; Lee, S; Mokhber-Shahin, LGross alpha beta measurement techniques are used for rapid radioanalytical screening of both solid and liquid samples for environmental, scientific and industrial purposes. A number of gross alpha beta measurement techniques are available depending on the sample matrix and each should report the gross or total alpha or beta radioactivity relative to the alpha or beta emitting radionuclide in the calibration source. To establish measurement accuracy and reliability, certified reference materials (CRMs) which are traceable to a national standard should be used to prepare a calibration source in the same geometry as the sample. it was our aim to develop solid CRMs for gross alpha beta techniques using a quartz mineral spiked with standardised and traceable radiotracer solutions. The quartz mineral was pulverised and then sieved to prepare a starting material which had a narrow particle size distribution range to reduce the likelihood of size fractionation. A standard operating procedure for the Malvern Mastersizer 2000 was developed to assess the adequacy of the starting material with the effect of ultrasonics and pump speed being investigated. The starting material vi/as spiked with either 241Am or spiking 99Sr/90Y to prepare the alpha CRM or beta CRM respectively. The solutions were standardised by ANSTO Radionuclide Metrology to provide direct traceability to the Austral an National Standard tor Radioactivity. Spiking was performed using the acetone bath method. The sieved quartz material was mixed with acetone in a large round-bottom flask and accurately known quantities of radionuclide solution added. The flask was rotated on a rotary evaporator tor a few hours to ensure an even distribution of the radionuclide through the quartz. The acetone was evaporated, the dry spiked quartz material transferred to a poly-ethylene bottle and further homogenised by shaking for a few hours using a Turbula mixer. Homogeneity testing using 10 aliquots from each CRM and radionuclide losses on the rotary evaporator glassware and mixing vessel were established using radiochemical separation and alpha spectrometry tor 24‘Am and Liquid Scintillation Counting (LSC) for 90Sr/90Y. Each sample for testing underwent a separation and purification process that included dissolution, precipitation and re-dissolution and column purification using Eichrom® pre-packed cartridge stack of TEVA®, TRU® and Sr-Spec® resins. Canberra Alpha Analyst and Apex Alpha Counting Software was used tor Alpha spectrometry and 90Sr/90Y was measured on a Packard Tri Carb 3lOOTR LSC. This CRM is intended to be used in gross alpha beta counting instrumentation such as gas flow proportional counters and plastic scintillator detector chambers in accordance with lSO18589-6 Measurement of radioactivity in the environment — Soil Part 6: Measurement of gross alpha and gross beta activities and ultimately to be available tor commercial use.
- ItemRadionuclide bioaccumulation in trees at an Australian legacy low-level waste site: concentration patterns in branches and foliage(American Nuclear Society, 2014-08-24) Wilsher, KL; Johansen, MP; Harrison, JJ; Payne, TE; Howitt, JA; Doran, G; Child, DP; Hotchkis, MAC; Thiruvoth, S; Mokhber-Shahin, L; Twining, JR; Vardanega, CR; Wong, HKYNot available
- ItemRadionuclide bioaccumulation patterns in vegetation at a legacy low-level waste site(Australian Nuclear Science and Technology Organisation, 2012-10-16) Wilsher, KL; Johansen, MP; Howitt, JA; Doran, G; Twining, JR; Child, DP; Dodson, JR; Dore, MJ; Harrison, JJ; Hotchkis, MAC; Mokhber-Shahin, L; Payne, TE; Thiruvoth, S; Wong, HKYThis study focuses on uptake of radionuclides (RN) into trees at a legacy low level radioactive waste site (the Little Forest Burial Ground (LFBG) near Lucas Heights in southern Sydney). Tree species included: Acacia longifolia longifolia; Syncarpia glomulifera; Eucalyptus paniculate; Leptospermum polygalifolium; and Banksia serrata. Branches – (wood and foliage) were sampled, and soil cores were collected around each tree. Analytical techniques included Inductively Coupled Plasma Atomic Emission Spectrometry and Mass Spectrometry, alpha and gamma spectrometry, Accelerator Mass Spectrometry and Cerenkov counting. Anthropogenic RN measured in trees and soils were 90Sr, 137Cs, 233U, 239+240Pu and 241Am. Median concentrations of RN in trees growing on, or near, the trenches (90Sr - 9.855 Bq/kg, 137Cs - 0.220 Bq/kg, 239+240Pu - 0.004 Bq/kg) were significantly higher than background trees (90Sr – 0.001 Bq/kg, 137Cs – n.d., 239+240Pu - 0.002 Bq/kg). Most trees had higher levels in foliage compared to wood. However; there was large variation among branches within the same tree. Uptake of radionuclides was quantified by the concentration ratio (CR), defined as average concentration in the tree to that of the surrounding soil. CR’s for trees growing around the trenches were an order of magnitude higher than for background trees, which is attributed to the trees taking up radionuclides directly from the subsurface. Our results better quantify the bio-available fraction of radionuclides in the environment at the LFBG, and reveal that site trees are bio-monitors of multiple radionuclides sourced from the sub-surface wastes.
- ItemRadionuclide distributions and migration pathways at a legacy trench disposal site(Elsevier B. V., 2020-01) Payne, TE; Harrison, JJ; Cendón, DI; Comarmond, MJ; Hankin, SI; Hughes, CE; Johansen, MP; Kinsela, AS; Mokhber-Shahin, L; Silitonga, A; Thiruvoth, S; Wilsher, KLThis paper examines the distributions of several anthropogenic radionuclides (239+240Pu, 241Am, 137Cs, 90Sr, 60Co and 3H) at a legacy trench disposal site in eastern Australia. We compare the results to previously published data for Pu and tritium at the site. Plutonium has previously been shown to reach the surface by a bath-tubbing mechanism, following filling of the former trenches with water during intense rainfall events. This has led to some movement of Pu away from the trenched area, and we also provide evidence of elevated Pu concentrations in shallow subsurface layers above the trenched area. The distribution of 241Am is similar to Pu, and this is attributed to the similar chemistry of these actinides and the likely in-situ generation of 241Am from its parent 241Pu. Concentrations of 137Cs are mostly low in surface soils immediately above the trenches. However, similar to the actinides, there is evidence of elevated 137Cs and 90Sr concentrations in shallow subsurface layers above the trenched area. While the subsurface radionuclide peaks suggest a mechanism of subsurface transport, their interpretation is complicated by the presence of soil layers added following disposals and during the subsequent years. The distribution of 90Sr and 137Cs at the ground surface shows some elevated levels immediately above the trenches which were filled during the final 24 months of disposal operations. This is in agreement with disposal records, which indicate that greater amounts of fission products were disposed in this period. The surface distribution of 239+240Pu is also consistent with the disposal documents. Although there is extensive evidence of a mobile tritium plume in groundwater, migration of the other radionuclides by this pathway is limited. The data highlight the importance of taking into account multiple pathways for the mobilisation of key radioactive contaminants at legacy waste trench sites. Crown Copyright © 2019 Published by Elsevier Ltd.
- ItemRadionuclide sorption studies of Co, Cs and Sr onto soils from an Australian legacy radioactive waste site(South Pacific Environmental Radioactivity Association, 2012-10-18) Gückel, K; Comarmond, MJ; Payne, TE; Chong, E; Mokhber-Shahin, LThis paper discusses results of radionuclide sorption studies on a soil profile taken from a low level radioactive waste site in South Eastern Australia, known as the Little Forest Burial Ground. Low level radioactive waste was buried at this site in a series of shallow trenches in the 1960s, and the site has been the focus of a field study in recent years. Measurable amounts of Co-60, Sr-90, Cs-137 and traces of actinides have been observed at this legacy waste site in some soils, groundwater and vegetation samples taken in close proximity to the disposal area. The sorption of Co, Cs and Sr was studied at four depth intervals from one corehole located near the trenches using radioactive tracers and a batch sorption method. Strong sorption was observed for Cs over the entire pH range studied, whereas the sorption of Co and Sr on the soils was pH dependent with sorption edges between pH 3 and pH 6. Distribution coefficients (Kd values) for Cs sorption were similar for each soil over the entire pH range, with variations of less than one order of magnitude between samples. However, the Kd values for Sr and Co sorption varied over two and three orders of magnitude, respectively, over the pH range studied. The bulk mineralogy of the soils was found to be similar with quartz, kaolinite and interstratified illite/smectite to be the main mineralogical phases with iron oxides and anatase as minor minerals in some soils. The BET surface areas of the bulk samples varied from 27 m2/g to 47 m2/g and no strong correlation of surface area with sorption was observed. The CEC of the bulk samples range between 10 and 24 cmol/kg. The CEC of the clay fractions were significantly higher, ranging from 21 to 34 cmol/kg and 34 to 55 cmol/kg for the < 2 μm and < 0.2 μm fractions, respectively. Further studies to elucidate the role of the various minerals with respect to sorption are in progress in order to assess the key site characteristics governing contaminant release and transport.
- ItemRadium and strontium binding by a modified bauxite refinery residue – isotope exchange studies of pH-dependence, reversibility and ageing(Geological Society of London, 2019-07-24) Clark, MW; Harrison, JJ; Payne, TE; Comarmond, MJ; Thiruvoth, S; Mokhber-Shahin, LThe pH-dependence and reversibility of radium (Ra) and strontium (Sr) binding to a modified bauxite refinery residue (MBRR), and the effects of sample ageing, were studied in laboratory uptake/leaching experiments. Natural 226Ra and stable strontium (Srnat) were placed in contact with the MBRR for an 8-day loading period (equilibrium pH c. 8.5). Following the addition of exchange isotopes 228Ra and 85Sr, the samples were then leached in pH-dependent experiments, where the pH was decreased incrementally from 9 to 3 over 7 h. A further suite of samples was aged at 4°, 23° and 65°C for 6 months after the initial addition of 226Ra and Srnat and then studied in a similar set of pH-dependent exchange experiments. The relative concentrations of the Ra and Sr isotope pairs (226Ra/228Ra and Srnat/85Sr) provided insights into the adsorption strength, incorporation, reversibility and ageing effects. The Srnat data showed that the amount of bound Sr released from aged MBRR samples as the pH decreases is substantially lower than the unaged sample, showing that Sr has been incorporated in less accessible phases during the ageing period. It appears that the uptake of 228Ra by the higher-temperature aged samples is somewhat stronger than the unaged samples; however, Ra isotope exchange plots for aged and unaged samples are similar. Consequently, the stronger binding of 228Ra by the higher-temperature aged samples is probably driven by translocation to kinetically less-favourable surface sites rather than a significant incorporation of Ra within the mineral solids during ageing. © 2022 Geological Society of London
- ItemUptake and release of radionuclides in wetland plants and soils(South Pacific Radioactivity Association, 2010-08-31) Johansen, MP; Twining, JR; Mokhber-Shahin, LWetland plants and soils can accumulate metals including naturally-occurring and anthropogenic radionuclides, and there has been much research performed on "wetlands as sinks." However, the stability of these wetland sinks, with their elevated concentrations of metals and radionuclides, depends on relatively constant water-supply and inundation conditions. Few studies have been performed to document the release rates of radionuclides from wetlands during hydrologic perturbations including the extended droughts and water diversions occurring in many parts of Australia over the past decade. We performed a scoping study to measure uptake, retention, and release rates of a range of gamma emitters (51Cr, 54Mn, 57Co, 60Co, 59Fe, 65Zn, 75Se, 89Sr, 109Cd, 134Cs) relative to Australian wetland plants and soils. Two types of plants (Phragmites australis and Cyperus exaltus), were grown in ten containers with variation in the root density (i.e., number of root-masses per container), and in the amount of Macquarie Marshes wetland soil mixed with a quartzite-pebble substrate. Constant levels of a tracer-water solution were maintained in all containers over a 30-day growth period, followed by clipping of shoots and draining of the containers. The root-soil combinations were allowed to dry intact at glasshouse ambient temperatures for 7 months to simulate a seasonal drying period, followed by a series of leach tests. Leachate was filtered (μ45) followed by gamma counting and analysed applying gamma-ray spectrometry. Several HPGe detectors with nominal efficiencies ranging from 35% to 50% were used. The results of the first two leach tests (L1 and L2) are available. Tracer activity concentrations in Ieachate samples typically trended lower as the root density in the containers increased. For example, the leachates from containers having four root masses had activity concentrations typically ∼50% lower than those with no roots. This occurred even though the root mass was a small fraction (<0.001) of the mass of the soil-pebble matrix suggesting that roots have a substantial accumulation effect on a per weight basis. The retention of tracers within the root-soil treatments was measured by comparing the ratio of activity concentrations in the "first flush” Ieachate (L1) to that of the second Ieachate (L2). For three tracers (54Mn, 57Co, and 59Fe) the L1/L2 ratios were ∼8-18 fold when roots were absent, but lower (0.4-2.9) when roots were present, suggesting that intact roots increase retention capacity over repeated wet-dry cycles for 54Mn, 57Co, and 59Fe. ln contrast, the L1/L2 ratios of the remaining tracers were relatively constant (1.3-3.9) regardless of the presence or absence of roots, or variation in root density. The increasing amounts (0%. 20%, 35%, and 50%) of organic-rich wetland soils from Macquarie Marshes present in the host soil-quartzite matrix corresponded to up to 100—fold decreases in Ieachate concentrations of 51Cr, 57Co, 60Co, 65Zn, 755e, 89Sr, and 134Cs. ln contrast, 54Mn, 59Fe, and 109Cd concentrations increased 2-12-fold with increasing soil amounts of up to 50%. Further Ieachate results, as well as analysis of concentrations in roots and shoots, are being conducted this year. A larger-scale study is being considered. This scoping study provides radiotracer release rates for wetlands soils subject to a seasonal drying cycle, and suggests that higher tracer release rates occur when plants are not present (no roots in the soil matrix) and that some tracers have order-of-magnitude higher concentrations in the initial leaching as compared with subsequent leaching. The retention of radionuclides by roots has implications of enhancing water quality by maintaining general health of wetland plant communities.