Browsing by Author "Wilsher, KL"

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    Accelerator mass spectrometry measurements of 233U in groundwater, soil and vegetation at a legacy radioactive waste site
    (Elsevier, 2024-06) Payne, TE; Harrison, JJ; Child, DP; Hankin, SI; Hotchkis, MAC; Hughes, CE; Johansen, MP; Thiruvoth, S; Wilsher, KL
    Low-level radioactive wastes were disposed at the Little Forest Legacy Site (LFLS) near Sydney, Australia between 1960 and 1968. According to the disposal records, 233U contributes a significant portion of the inventory of actinide activity buried in the LFLS trenches. Although the presence of 233U in environmental samples from LFLS has been previously inferred from alpha-spectrometry measurements, it has been difficult to quantify because the 33U and 234U α-peaks are superimposed. Therefore, the amounts of 233U in groundwaters, soils and vegetation from the vicinity of the LFLS were measured using accelerator mass spectrometry (AMS). The AMS results show the presence of 233U in numerous environmental samples, particularly those obtained within, and in the immediate vicinity of, the trenched area. There is evidence for dispersion of 233U in groundwater (possibly mobilised by co-disposed organic liquids), and the data also suggest other sources of 233U contamination in addition to the trench wastes. These may include leakages and spills from waste drums as well as waste burnings, which also occurred at the site. The AMS results confirm the historic information regarding disposal of 233U in the LFLS trenches. The AMS technique has been valuable to ascertain the distribution and environmental behaviour of 233U at the LFLS and the results demonstrate the applicability of AMS for evaluating contamination of 233U at other radioactive waste sites. © 2024 Australian Nuclear Science and Technology Organisation. Published by Elsevier Ltd. This is an open access article under the CC BY license
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    Assessment of radionuclide distributions at an Australian legacy radioactive waste site
    (South Pacific Radioactivity Association, 2010-09-01) Payne, TE; Cendón, DI; Collins, RN; Dore, M; Hankin, SI; Harrison, JJ; Hughes, CE; Johansen, MP; Thiruvoth, S; Twining, JR; Wilsher, KL
    During the 1960s, low level radioactive waste was buried in shallow trenches at a disposal site in south-eastern Australia, known as the Little Forest Burial Ground. This paper discusses preliminary findings of research into the distribution of radionuclides at the site, including soils, groundwater and biota. In particular, we are studying the mobility of radionuclides; and their uptake by plants, insects and small animals. Groundwater monitoring indicates that there has been limited movement of radioactivity, other than a tritium plume that extends at least 100 m. The tritium results are being used to define the groundwater flowpaths, and the effects of seasonal and climatic factors. The pattern of tritium distribution suggests that the source of tritium is predominantly within the waste materials. However, tritium derived from a nearby municipal landfill contributes to tritium concentrations in some groundwaters, with smaller amounts from cosmogenic tritium and atmospheric deposition originating from the nearby HIFAR reactor (shut down in 2007). The tritium data provide a record of water movement against which the relative mobility of other radionuclides can be assessed. There are measurable amounts of 60Co, 90Sr, 137Cs and traces of actinides in some soils, groundwater and vegetation samples taken in close proximity to the disposal area. Isotopic ratios such as δ13C, δ180, δ2H, δ34S and 87Sr/86Sr are being measured in groundwater, in addition to the radioactive isotopes originating from the disposed wastes. Synchrotron EXAFS and XANES studies are being applied to study elemental chemical environments and oxidation states in the soils at the site. We have recently undertaken a major geophysical investigation and drilling program; and installation of an improved array of water sampling boreholes is planned. Therefore, many more samples of groundwater and soils are becoming available for analysis.
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    Challenges in the radiochemical separation of marine samples from the Montebello Islands
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Thiruvoth, S; Child, DP; Harrison, JJ; Johansen, MP; Silitonga, A; Vardanega, CR; Wilsher, KL; Wong, HKY
    The Montebello Islands, located off the North Western coast of Western Australia, was used as a nuclear weapons test site by the British government in the 1950s. Three nuclear tests were conducted around the islands. The first in 1952 (W818) detonated in the hull of the HMS Plym anchored in 12 m of water between Alpha and Trimouille Islands, and the second and third tests (MOSAIC G1 and G2) were detonated on 30 m Aluminium towers in May and June 1956, G1 on the Northern Western tip of Trimouille island and G2, the largest test conducted in Australian territory, on Alpha island. The fallout from these tests deposited long-lived anthropogenic radionuclides on nearby islands and ocean surface, host to an array of animals and plants. Marine sand, marine sediment, algae, fish, turtles and turtle eggs, among others, were sampled from the surrounding zones for dose assessment studies, thirty-nine of which were processed for actinide and strontium analysis. Due to the expected presence of discrete radioactive particles in some matrices a three step digestion method was applied to obtain complete dissolution of sample material. To overcome sample heterogeneity, the digest solution was sub-sampled for actinide and Sr-90 analysis by alpha spectrometry and liquid scintillation analysis, for plutonium isotopic analysis by AMS, and for elemental analysis by ICPAES/MS. The radiochemical separation method developed at ANSTO for Am, Pu, Th, U, and Sr for terrestrial soils and sediments (Harrison et al, 2011) was adapted to samples from the marine environment. However, some sample matrices proved to be challenging in achieving acceptable chemical recoveries of strontium due to the high concentrations of native calcium. This current study will discuss the methods used, and challenges overcome, in radiochemical separation for alpha spectrometry and liquid scintillation analysis for a wide range of sample types.
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    Establishing 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, HKY
    Australia’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.
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    Identification and quantification of 233U at a legacy waste site
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Harrison, JJ; Child, DP; Hotchkis, MAC; Payne, TE; Thiruvoth, S; Wilsher, KL
    The Little Forest Burial Ground (LFBG), located within the Australian Nuclear Science and Technology Organisation (ANSTO) buffer zone, was used to dispose of low level radioactive waste in shallow trenches during the 1960s. Operational records suggest that natural and anthropogenic radionuclides were disposed of, including uranium-233 (233U), a fissile isotope of uranium. This paper outlines how 233U was identified and then quantified in environmental samples from LFBG in the presence of other uranium isotopes. Alpha spectrometry sources were prepared using 232U as a tracer and counted to give a qualitative indication of 233U from the combined 233+234U activity. The primary region of interest (ROI) of 233U is a doublet peak, with emission energies of 4.784 MeV (13%) and 4.824 MeV (84%). This peak, if present in an alpha spectrum, will overlap with the primary ROI of 234U, also a doublet of 4.722 MeV (28%) and 4.775 MeV (71%). Based on alpha spectrometry results, samples thought to contain 233U were then prepared for Accelerator Mass Spectrometry (AMS). AMS was used to measure the 234U/233U isotope ratio. The isotope dilution method, with 236U spike, was not able to be used with samples from this study site as low levels of this anthropogenic isotope have also been detected. Instead, the isotope ratio 234U/233U from AMS was used with the combined 233+234U activity from alpha spectrometry to derive the 233U activity. This combination of techniques enables 233U to be quantified in these types of environmental samples.
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    Identification of sources and processes in a low-level radioactive waste site adjacent to landfills: groundwater hydrogeochemistry and isotopes
    (Taylor & Francis Group, 2014-11-25) Cendón, DI; Hughes, CE; Harrison, JJ; Hankin, SI; Johansen, MP; Payne, TE; Wong, HKY; Rowling, B; Vine, M; Wilsher, KL; Guinea, A; Thiruvoth, S
    Multiple tracer-element and isotope approaches were applied at a 1960s-era low-level radioactive waste burial site located in the Lucas Heights area on the southwest urban fringe of Sydney, Australia. The site is situated among other municipal and industrial (solid and liquid) waste disposal sites causing potential mixing of leachates. Local rainfall contains marine-derived major ion ratios that are modified during infiltration depending on waste interactions. The local geology favours the retention of contaminants by ion-exchange processes within the clay-rich soils and the shale layer underlying the burial site. Local soils experience periodic infiltration and wetting fronts that can fully saturate the waste trenches (bathtub effect) while surrounding soils are mostly unsaturated with discontinuous perched lenses. Within the trenches, the degradation of organic matter results in localised methanogenesis, as suggested by enriched δ2H and δ13CDIC values in adjacent subsurface water. Movement of contaminants from the trenches is indicated by Na+, Br? and I? concentrations, variations in 87Sr/86Sr, enriched δ13CDIC values and evolution of δ34S of dissolved sulfate in perched water bodies above the shale. Although transport is limited by the low transmissivity of the clay-rich soils, migration and mixing processes are indicated by the variation of concentrations with distance from the trenches, disappearance of δ2H enrichments, mixing with other sources of Sr and sulfate isotope fractionations. The depth distribution of waste-derived contaminants (specifically 3H and Be) between the perched water surrounding the trenches, and the underlying shale and sandstone layers, indicates limited downward transport of contaminants. Past removal of the shale layer in an adjacent site, Harrington's Quarry, has facilitated the mixing of some municipal waste leachates (characterised by circum-neutral pH, high alkalinity, low sulfate, high 3H, high Be, enriched δ2H and δ13CDIC) into the underlying groundwater system as suggested by high TDS, Cl?/Br? ratios, Be and 3H found in deeper wells. This study demonstrates the applicability of using trace elements, stable- and radio-isotopes to document the existing geochemistry and the contaminant transport from the waste trenches. The multiple tracer approach addresses the complexities of transport at the site and differentiates various municipal, industrial and radioactive waste sources. © 2014 Informa UK Limited
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    Influence of dissolved silicate on rates of Fe(II) oxidation
    (American Chemical Society, 2016-10-05) Kinsela, AS; Jones, AM; Bligh, MW; Pham, AN; Collins, RN; Harrison, JJ; Wilsher, KL; Payne, TE; Waite, TD
    Increasing concentrations of dissolved silicate progressively retard Fe(II) oxidation kinetics in the circum-neutral pH range 6.0–7.0. As Si:Fe molar ratios increase from 0 to 2, the primary Fe(III) oxidation product transitions from lepidocrocite to a ferrihydrite/silica-ferrihydrite composite. Empirical results, supported by chemical kinetic modeling, indicated that the decreased heterogeneous oxidation rate was not due to differences in absolute Fe(II) sorption between the two solids types or competition for adsorption sites in the presence of silicate. Rather, competitive desorption experiments suggest Fe(II) was associated with more weakly bound, outer-sphere complexes on silica-ferrihydrite compared to lepidocrocite. A reduction in extent of inner-sphere Fe(II) complexation on silica-ferrihydrite confers a decreased ability for Fe(II) to undergo surface-induced hydrolysis via electronic configuration alterations, thereby inhibiting the heterogeneous Fe(II) oxidation mechanism. Water samples from a legacy radioactive waste site (Little Forest, Australia) were shown to exhibit a similar pattern of Fe(II) oxidation retardation derived from elevated silicate concentrations. These findings have important implications for contaminant migration at this site as well as a variety of other groundwater/high silicate containing natural and engineered sites that might undergo iron redox fluctuations. © 2016 American Chemical Society
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    Installation of a pilot experimental trench at the Little Forest legacy site
    (Australian Nuclear Science and Technology Organisation, 2018-07-30) Payne, TE; Kinsela, AS; Rowling, B; Hankin, SI; Cendón, DI; Comarmond, MJ; Bligh, MW; Hughes, CE; Anderson, D; Wilsher, KL
    During 2017, a pilot experimental trench was constructed at the Little Forest Legacy Site (LFLS). The objective of installing this trench was to facilitate experimental field-work aimed at further characterising the site, in particular the hydrology of the excavated trenches and of the near-surface layers in which the trenches are located. The test trench is of similar depth to the waste disposal trenches at the legacy site (3 metres) and extends 6 m in length. However, unlike the disposal trenches, the experimental trench contains no waste materials of any kind. Instead, the trench contains a number of sampling points and other instrumentation, and is back filled with river gravel to provide a uniform composition and maintain structural stability. It is intended that the pilot trench will be followed by other trenches with specific experimental objectives. The purposes of this report are to discuss the background, rationale for, and implementation of the facility; to provide a detailed description of the pilot trench; and to compile information and photographs documenting the excavation process. Although some preliminary hydrological data and comparisons with the legacy trenches are presented, the scientific data will be fully discussed and interpreted in future scientific reports.
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    Installation of an experimental trench at the Little Forest Legacy Site
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Payne, TE; Kinsela, AS; Bligh, M; Anderson, D; Rowling, B; Hughes, CE; Hankin, SI; Cendón, DI; Wilsher, KL; Comarmond, MJ
    During 2017, a pilot experimental trench was constructed at the Little Forest Legacy Site (LFLS), a 1960s era disposal site for low-level radioactive waste. The objective of installing this trench was to facilitate experimental field-work aimed at further characterising the site, in particular the hydrology of the excavated trenches and of the near-surface layers in which the trenches are located. The test trench is of similar depth to the waste disposal trenches at the legacy site (8 metres) and extends 6 m in length. However, unlike the disposal trenches, the experimental trench does not contain waste materials. instead, the trench contains a number of sampling points and other instrumentation, and is back filled with river gravel to provide a uniform composition and maintain structural stability. in this paper, the excavation of the trench is described, together with observations made during the excavation. in addition, some preliminary hydrological data and comparisons with the legacy trenches are presented.
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    Methodology improvement: separation and measurement of uranium, thorium, americium, plutonium and strontium in large mass environmental samples
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Harrison, JJ; Thiruvoth, S; Wilsher, KL
    This paper outlines recent method modifications implemented for the radiochemical analysis of large volume groundwater, soil and ashed tree samples. The issues addressed include the formation of silica gel, interference of polonium-210 (210Po) with the uranium-232 (232U) tracer peak in U spectra, and broadening of alpha peaks in thorium (Th) and americium (Am) spectra due to chemicals derived from separation resins. A silica gel forms in evaporated groundwater samples that increases co-precipitate volumes and sample load solution volumes. If not effectively removed, this silica gel will clog the separation resin cartridges. The addition of polyethylene glycol (PEG) followed by high speed centrifugation and filtering after co-precipitation enables the removal of this silica gel. 210Po, present in some ashed vegetation samples with activities up to 500 Bq/kg, was sometimes found in the U fraction. The 210Po alpha emission peak overlaps the 232U tracer peak, preventing accurate chemical yield determination. An additional wash step between Am and U elution was implemented to remove 210Po from the U fraction. Organic compounds from the TEVA TM and TRU TM separation resins are leached into the Th and Am fractions respectively, resulting in broad alpha peaks. Evaporation and dilution of the fractions prior to alpha source preparation or the use of an Eichrom Pre-filter cartridge during elution is required.
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    Methods for the determination of U-238, Pu-239, Pu-240 and Am-241 from Little Forest Legacy Site (LFLS) groundwater using on-line SeaFast pre-concentration coupled to ICPMS
    (South Pacific Environmental Radioactivity Association, 2018-11-06) Rowling, B; Wong, HKY; Harrison, JJ; Wilsher, KL; Payne, TE
    Analyses of groundwaters within Little Forest Legacy Site in eastern Australia have been performed using a number of techniques. Uranium concentration has been analysed using a combination of ICPMS and alpha spectrometry whilst plutonium and americium activity measurements have been performed using alpha spectrometry and accelerated mass spectrometry (AMS). The SeaFAST is an automated on-line lCPMS sample introduction system without sample preparation required for the determination of ultra-trace metals in undiluted water samples. The use of sample pre-concentration and procedural blanks eliminates matrix effects whilst improving reliability. This system is often applied to swiftly analyse for rare earth elements as well as uranium and thorium in surface and groundwater systems. The development of a method which could be used to analyse for plutonium and americium could extend the application of the SeaFAST-ICPMS system whilst also providing a complementary or quick screening technique. This paper presents the significant steps in developing and validating the SeaFAST-lCPMS method as well as reporting isotope ratio results.
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    Plutonium 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, MD
    This 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
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    Preparation 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, L
    Gross 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.
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    Radionuclide 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, HKY
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    Radionuclide 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, HKY
    This 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.
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    Radionuclide 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, KL
    This 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.
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    Solution speciation of plutonium and americium at an Australian legacy radioactive waste disposal site
    (ACS Publications, 2014-08-15) Ikeda-Ohno, A; Harrison, JJ; Thiruvoth, S; Wilsher, KL; Wong, HKY; Johansen, MP; Waite, TD; Payne, TE
    During the 1960s, radioactive waste containing small amounts of plutonium (Pu) and americium (Am) was disposed in shallow trenches at the Little Forest Burial Ground (LFBG), located near the southern suburbs of Sydney, Australia. Because of periodic saturation and overflowing of the former disposal trenches, Pu and Am have been transferred from the buried wastes into the surrounding surface soils. The presence of readily detected amounts of Pu and Am in the trench waters provides a unique opportunity to study their aqueous speciation under environmentally relevant conditions. This study aims to comprehensively investigate the chemical speciation of Pu and Am in the trench water by combining fluoride coprecipitation, solvent extraction, particle size fractionation, and thermochemical modeling. The predominant oxidation states of dissolved Pu and Am species were found to be Pu(IV) and Am(III), and large proportions of both actinides (Pu, 97.7%; Am, 86.8%) were associated with mobile colloids in the submicron size range. On the basis of this information, possible management options are assessed. © 2014, American Chemical Society.
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    Trench 'bathtubbing’ and surface plutonium contamination at a legacy radioactive waste site
    (American Chemical Society, 2013-11-20) Payne, TE; Harrison, JJ; Hughes, CE; Johansen, MP; Thiruvoth, S; Wilsher, KL; Cendón, DI; Hankin, SI; Rowling, B; Zawadzki, A
    Radioactive waste containing a few grams of plutonium (Pu) was disposed between 1960 and 1968 in trenches at the Little Forest Burial Ground (LFBG), near Sydney, Australia. A water sampling point installed in a former trench has enabled the radionuclide content of trench water and the response of the water level to rainfall to be studied. The trench water contains readily measurable Pu activity (∼12 Bq/L of 239+240Pu in 0.45 μm-filtered water), and there is an associated contamination of Pu in surface soils. The highest 239+240Pu soil activity was 829 Bq/kg in a shallow sample (0–1 cm depth) near the trench sampling point. Away from the trenches, the elevated concentrations of Pu in surface soils extend for tens of meters down-slope. The broader contamination may be partly attributable to dispersion events in the first decade after disposal, after which a layer of soil was added above the trenched area. Since this time, further Pu contamination has occurred near the trench-sampler within this added layer. The water level in the trench-sampler responds quickly to rainfall and intermittently reaches the surface, hence the Pu dispersion is attributed to saturation and overflow of the trenches during extreme rainfall events, referred to as the ‘bathtub’ effect. © 2013 American Chemical Society
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    Using hydro-geochemistry and isotopes to trace groundwater flow from Little Forest Burial Ground and surrounding landfills
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Cendón, DI; Hughes, CE; Harrison, JJ; Hanklin, SI; Johansen, MP; Payne, TE; Wong, HKY; Rowling, B; Vine, M; Wilsher, KL; Guinea, A; Thiruvoth, S
    Multiple tracer-element and isotope approaches were used to study groundwater near a legacy low-level radioactive waste burial site surrounded by municipal and industrial waste sites. The interaction of rainfall, with its marine-derived major ion ratios, and waste from the sites is apparent, however, clay-rich soils and shale at the site tend to retain many contaminants via ion exchange and other processes. High permeability of the disposal trenches provides a pathway for groundwater recharge, with discontinuous perched groundwater lenses found in their vicinity. Within the trenches, the degradation of organic matter results in localised methanogenesis, as suggested by enriched δ2H and δ13CDIC in adjacent subsurface water. Movement of contaminants from the waste sites is indicated by Na+, Brˉ and Iˉ concentrations, variations in 87Sr/86Sr, enriched δ13CDIC and evolution of δ34S of dissolved sulfate in perched water bodies above the shale. There is clear evidence of a tritium plume from the LFBG trenches, although the adjacent landfills provide an additional tritium source. Waste burial records show that over 1000 kg of Be (mostly BeO) were disposed in the LFBG trenches. However, beryllium concentrations in groundwaters near the trenches are quite low, and appear more likely to be controlled by the host lithologies and the other sources of contamination in the vicinity, rather than by leaching of Be from the LFBG waste. Past removal of the shale layer in an adjacent site, Harrington’s Quarry, has led to the mixing of municipal waste leachates into the underlying groundwater system as suggested by high TDS, Cl−/Br− ratios, Be, and 3H found in deeper wells. The multiple tracer approach addresses the complexities of transport at the site and differentiates various municipal, industrial, and radioactive waste sources