Browsing by Author "Thiruvoth, S"
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- ItemAccelerator 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, KLLow-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
- ItemAccumulation of plutonium in mammalian wildlife tissues following dispersal by accidental-release tests(Elsevier, 2016-01-01) Johansen, MP; Child, DP; Caffrey, EA; Harrison, JJ; Hotchkis, MAC; Payne, TE; Ikeda-Ohno, A; Thiruvoth, S; Beresford, NA; Twining, JR; Davis, EWe examined the distribution of plutonium (Pu) in the tissues of mammalian wildlife inhabiting the relatively undisturbed, semi-arid former Taranaki weapons test site, Maralinga, Australia. The accumulation of absorbed Pu was highest in the skeleton (83% ± 6%), followed by muscle (10% ± 9%), liver (6% ± 6%), kidneys (0.6% ± 0.4%), and blood (0.2%). Pu activity concentrations in lung tissues were elevated relative to the body average. Foetal transfer was higher in the wildlife data than in previous laboratory studies. The amount of Pu in the gastrointestinal tract was highly elevated relative to that absorbed within the body, potentially increasing transfer of Pu to wildlife and human consumers that may ingest gastrointestinal tract organs. The Pu distribution in the Maralinga mammalian wildlife generally aligns with previous studies related to environmental exposure (e.g. Pu in humans from worldwide fallout), but contrasts with the partitioning models that have traditionally been used for human worker-protection purposes (approximately equal deposition in bone and liver) which appear to under-predict the skeletal accumulation in environmental exposure conditions. © 2015, Elsevier Ltd.
- ItemAnthropogenic radionuclides persist in marine sediment at the Montebello Islands nuclear legacy site in Western Australia(South Pacific Environmental Radioactivity Association, 2022-11-28) Williams-Hoffman, M; Johansen, MP; Lavery, P; Thiruvoth, S; Serrano, O; Masqué, PIn 1952 and 1956 the UK government conducted three atmospheric nuclear fission tests in the Montebello Islands, an archipelago approximately 100 km off the coast of northern Western Australia. Radioactive contamination from the tests was deposited locally across the archipelago in both terrestrial and marine environments but was investigated minimally in the decades that followed. This is particularly true for the marine environment which is composed of various distinct ecosystems – from mangroves to open marine channels and is home to a diverse trophic web of marine organisms. To understand the extent and persistence of anthropogenic radionuclides introduced by the tests into this region, we aim to establish the distribution of anthropogenic radionuclides in the marine surface sediments throughout the archipelago. Here we present the results on activity concentrations and distributions of 90Sr, 137Cs, 238 Pu, 239&240Pu and 241Am due to their long half lives and their potential to impart radiological dose to organisms existing at the sediment-water interface. Quantification of anthropogenic and naturally occurring radionuclides in surface and core samples was completed by alpha spectrometry, Cherenkov counting and gamma spectrometry. Activity concentrations of 90Sr, 137Cs, 238 Pu, 239&240Pu and 241Am were highest around the detonation locations in the north of the archipelago in surface sediment samples. Observable activity concentrations also persist in the north-west of the detonation locations, reflecting the direction of the original fallout plumes from the weapons. One additional location showed higher activity concentrations of 90Sr, 137Cs, 238 Pu, 239&240Pu and 241Am in comparison to other locations within the archipelago (121 Bq/kg, 1.6 Bq/kg, 80 Bq/kg, 402 Bq/kg and 28 Bq/kg respectively). This sample was collected 26 km south of the nearest detonation site and was originally selected as an environmental control outside of the state marine park boundaries, suggesting migration of anthropogenic radionuclides has occurred in the 70 years since the detonations took place. Sediment cores were also taken from different marine environments of the region, including at the bottom of the crater created by Operation Hurricane, which involved the detonation of a naval ship in shallow water in 1952. 210Pb was analysed to assess the sedimentation rates over the last century across the cores. In most instances, mixing dominated throughout the sediment core profiles. This reflects the highly dynamic and turbulent nature of the region, subject to seasonal cyclones and fast-moving tides within the archipelago. The exception to this observed mixing was found in a single core, the ‘Hurricane Core’, taken in the bottom of the Operation Hurricane crater. 137Cs and 241Am activity concentrations of this core showed a clear peak in activity at 50 cm depth; an order of magnitude above those found in similar parts of the region within surface sediments. The maximum activity concentrations of 180 Bq/kg and 66 Bq/kg for 137Cs and 241Am respectively were established in the core at 50 cm depth, with the closest surface sediment activity concentrations established at 56 Bq/kg and 20 Bq/kg.
- ItemThe application of radiochronometry during the 4th collaborative materials exercise of the nuclear forensics international technical working group (ITWG)(Springer Nature, 2018-02-06) Kristo, MJ; Williams, R; Gaffney, AM; Kayzar-Boggs, TM; Schorzman, KC; Lagerkvist, P; Vesterlund, A; Ramebäck, H; Nelwamondo, AN; Kotze, D; Song, K; Lim, SH; Han, SH; Lee, CG; Okubo, A; Maloubier, D; Cardona, D; Samuleev, P; Dimayuga, I; Varga, Z; Wallenius, M; Mayer, K; Loi, E; Keegan, EA; Harrison, JJ; Thiruvoth, S; Stanley, FE; Spencer, KJ; Tandon, LIn a recent international exercise, 10 international nuclear forensics laboratories successfully performed radiochronometry on three low enriched uranium oxide samples, providing 12 analytical results using three different parent-daughter pairs serving as independent chronometers. The vast majority of the results were consistent with one another and consistent with the known processing history of the materials. In general, for these particular samples, mass spectrometry gave more accurate and more precise analytical results than decay counting measurements. In addition, the concordance of the 235U–231Pa and 234U–230Th chronometers confirmed the validity of the age dating assumptions, increasing confidence in the resulting conclusions. © 2018 U.S. Government
- ItemAssessment 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, KLDuring 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.
- ItemChallenges 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, HKYThe 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.
- ItemDecoding an unexpected mystery at the Montebello Islands(South Pacific Environmental Radioactivity Association, 2022-11-30) Williams-Hoffman, M; Johansen, MP; Lavery, PL; Thiruvoth, S; Serrano, O; Masqué, PDuring the 1950’s three nuclear tests were conducted in the Montebello Islands in Western Australia by the UK government. The tests introduced a radioactive legacy into the surrounding marine environment but were investigated minimally immediately after and in the decades that followed. Work is currently underway to quantify the persistence and migration of anthropogenic radionuclides within the island archipelago’s marine sediments. Activity concentrations of studied radionuclides (137Cs, 238Pu, 239&240Pu and 241Am) in surface sediments so far have concentrated within a 5 km radius of the three ground zero locations and in the north-west of the islands inline with the original fallout plume trajectories. However, one sampling location does not fit within this originally hypothesised pattern of distribution. This single site, called the Lowendal Islands site, was 26 km south of the detonation ground zero locations and originally sampled as an environmental background. Activity concentrations of studied radionuclides were the second highest of all surface sediments collected (1.6 Bq kg-1, 80 Bq kg-1, 402 Bq kg-1 and 28 Bq kg-1 respectively). Four initial theories are proposed to explain this mystery: currents, air movement, rafting or human involvement. Current analysis indicates that either rafting or human involvement are most likely, based on reviews of historical data, knowledge of regional water movement and 241Am/240Pu/239Pu ratios.
- 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.
- ItemIdentification 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, KLThe 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.
- ItemIdentification 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, SMultiple 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
- ItemMeasurement of 233U/234U ratios in contaminated groundwater using alpha spectrometry(Elsevier, 2016-01-01) Harrison, JJ; Payne, TE; Thiruvoth, S; Child, DP; Johansen, MP; Hotchkis, MACThe uranium isotope 233U is not usually observed in alpha spectra from environmental samples due to its low natural and fallout abundance. It may be present in samples from sites in the vicinity of nuclear operations such as reactors or fuel reprocessing facilities, radioactive waste disposal sites or sites affected by clandestine nuclear operations. On an alpha spectrum, the two most abundant alpha emissions of 233U (4.784 MeV, 13.2%; and 4.824 MeV, 84.3%) will overlap with the 234U doublet peak (4.722 MeV, 28.4%; and 4.775 MeV, 71.4%), if present, resulting in a combined 233+234U multiplet. A technique for quantifying both 233U and 234U from alpha spectra was investigated. A series of groundwater samples were measured both by accelerator mass spectrometry (AMS) to determine 233U/234U atom and activity ratios and by alpha spectrometry in order to establish a reliable 233U estimation technique using alpha spectra. The Genie™ 2000 Alpha Analysis and Interactive Peak Fitting (IPF) software packages were used and it was found that IPF with identification of three peaks (234U minor, combined 234U major and 233U minor, and 233U major) followed by interference correction on the combined peak and a weighted average activity calculation gave satisfactory agreement with the AMS data across the 233U/234U activity ratio range (0.1–20) and 233U activity range (2–300 mBq) investigated. Correlation between the AMS 233U and alpha spectrometry 233U was r2 = 0.996 (n = 10). © 2015, Elsevier Ltd.
- ItemMethodology 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, KLThis 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.
- ItemMigration of 239, 240PU and 233U from a low-level radioactive waste site(South Pacific Environmental Radioactivity Association, 2022-11-23) Harrison, JJ; Payne, TE; Child, DP; Hotchkis, MAC; Johansen, MP; Thiruvoth, S; Zawadzki, ALow-level measurements of 239,240Pu and 233U have been used to investigate the migration pathways of these radionuclides in the vicinity of a legacy waste site near Sydney, Australia. Between the years of 1960 to 1968 mixed wastes, including laboratory waste, were disposed at the site in shallow, unlined trenches, and disposal records indicate that the waste contained small masses of plutonium (several grams) and other long-lived radionuclides, including 233U. Measurements of 239,240Pu and 233U in environmental matrices of soil, sediment, water, and vegetation have been made using a combination of accelerator mass spectrometry and alpha spectrometry techniques. Both 239,240Pu and 233U concentrations and 240/239Pu atom ratios have been used to assess the migration of these actinides. A site specific 240/239Pu atom ratio has been established (0.084) which is distinctly different from the ratio found elsewhere in the Sydney Basin due to nuclear weapons testing fallout thereby providing an indicator of plutonium originating from the site. 233U has very low abundance in nuclear weapons test fallout therefore the only plausible source of elevated 233U in the environment at and around this site is uranium migration from the disposal site. The concentrations of 239,240Pu and 233U typically decrease with distance from the disposal trenches. The 239,240Pu concentrations in soils and sediments at distance are within the range seen elsewhere in Australia due to atmospheric nuclear weapons fallout. However, the presence of 233U and the influence of the site specific 240/239Pu atom ratio on the local plutonium isotopic signature indicates that these actinides are persistent in soils, sediments and waters hundreds of metres away and vegetation tens of metres away from the disposal trenches. Multiple migration mechanisms have been considered for actinides derived from the site, including surface water flow from the disposal trenches, particulate transport during heavy rainfall events, vegetation uptake, contamination which may have occurred during disposal operations and airborne particulate transport.
- ItemPlutonium and other radionuclides persist across marine-to-terrestrial ecotopes in the Montebello Islands sixty years after nuclear tests(Elsevier, 2019-11-15) Johansen, MP; Child, DP; Cresswell, T; Harrison, JJ; Hotchkis, MAC; Howell, NR; Johansen, A; Sdraulig, S; Thiruvoth, S; Young, EL; Whiting, SDSince the 1956 completion of nuclear testing at the Montebello Islands, Western Australia, this remote uninhabited island group has been relatively undisturbed (no major remediations) and currently functions as high-value marine and terrestrial habitat within the Montebello/Barrow Islands Marine Conservation Reserves. The former weapons testing sites, therefore, provide a unique opportunity for assessing the fate and behaviour of Anthropocene radionuclides subjected to natural processes across a range of shallow-marine to island-terrestrial ecological units (ecotopes). We collected soil, sediment and biota samples and analysed their radionuclide content using gamma and alpha spectrometry, photostimulated luminescence autoradiography and accelerator mass spectrometry. We found the activity levels of the fission and neutron-activation products have decreased by ~hundred-fold near the ground zero locations. However, Pu concentrations remain elevated, some of which are high relative to most other Australian and international sites (up to 25,050 Bq kg−1 of 239+240+241Pu). Across ecotopes, Pu ranked from highest to lowest in the following order: island soils > dunes > foredunes > marine sediments > and beach intertidal zone. Low values of Pu and other radionuclides were detected in all local wildlife tested including endangered species. Activity concentrations ranked (highest to lowest) terrestrial arthropods > terrestrial mammal and reptile bones > algae > oyster flesh > whole crab > sea turtle bone > stingray and teleost fish livers > sea cucumber flesh > sea turtle skin > teleost fish muscle. The three detonations (one from within a ship and two from 30 m towers) resulted in differing contaminant forms, with the ship detonation producing the highest activity concentrations and finer more inhalable particulate forms. The three sites are distinct in their 240/239Pu and 241/239Pu atom ratios, including the Pu transported by natural process or within migratory living organisms. Crown Copyright © 2019 Published by Elsevier B.V
- ItemPlutonium in wildlife and soils at the Maralinga legacy site: persistence over decadal time scales(Elsevier Science Ltd, 2014-05-01) Johansen, MP; Child, DP; Davis, E; Doering, C; Harrison, JJ; Hotchkis, MAC; Payne, TE; Thiruvoth, S; Twining, JR; Wood, MDThe mobility of plutonium (Pu) in soils, and its uptake into a range of wildlife, were examined using recent and similar to 25 year old data from the Taranaki area of the former Maralinga weapons test site, Australia. Since its initial deposition in the early 1960s, the dispersed Pu has been incorporated into the soil profile and food chain through natural processes, allowing for the study of Pu sequestration and dynamics in relatively undisturbed semi-arid conditions. The data indicate downward mobility of Pu in soil at rates of similar to 0.2-0.3 cm per year for the most mobile fraction. As a result, while all of the Pu was initially deposited on the ground surface, approximately 93% and 62% remained in the top 0-2 cm depth after 25- and 50-years respectively. No large-scale lateral spreading of the Taranaki plume was observed. Pu activity concentrations in 0-1 cm soils with biotic crusts were not elevated when compared with nearby bare soils, although a small number of individual data suggest retention of Pu-containing particles may be occurring in some biotic crusts. Soil-to-animal transfer, as measured by concentration ratios (CRwo-soil), was 4.1E-04 (Geometric Mean (GM)) in mammals, which aligns well with those from similar species and conditions (such as the Nevada Test Site, US), but are lower than the GM of the international mammal data reported in the Wildlife Transfer Database (WTD). These lower values are likely due to the presence of a low-soluble, particulate form of the Pu in Maralinga soils. Arthropod concentration ratios (3.1E-03 GM), were similar to those from Rocky Flats, US, while values for reptiles (2.0E-02 GM) were higher than the WTD GM value which was dominated by data from Chernobyl. Comparison of uptake data spanning approximately 30 years indicates no decrease over time for mammals, and a potential increase for reptiles. The results confirm the persistence of bioavailable Pu after more than 50 years since deposition, and also the presence of larger-sized particles which currently affect CRwo-soil calculations, and which may serve as an ongoing source of bioavailable Pu as they are subjected to weathering into the future. © 2014, Elsevier Ltd.
- ItemPlutonium transfer to wildlife at legacy sites(University of Georgia, 2013-06-16) Johansen, MP; Child, DP; Harrison, JJ; Kamboj, S; Kuhne, WW; Payne, TE; Thiruvoth, S; Wood, MDWhen internalized within an organism’s body, plutonium (Pu) can be important in dose calculation due to its relatively high-energy alpha emissions (~5-6 MeV). In this paper we quantify transfer of Pu to a range of wildlife types at legacy nuclear weapons sites and evaluate the importance of body tissue Pu distribution in the transfer of Pu through the food chain. The paper presents new data from Maralinga, Australia, as well as past data from terrestrial and marine settings of the US nuclear research program.
- ItemPlutonium uptake in biota at former nuclear sites(Australian Nuclear Association, 2013-10-11) Johansen, MP; Child, DP; Doering, C; Harrison, JJ; Hotchkis, MAC; Kamboj, W; Kuhne, WW; Payne, TE; Thiruvoth, S; Twining, JR; Wood, MDPlutonium (Pu) is of ongoing interest as worldwide inventories continue to increase and plans for permanent storage of Pu wastes have stalled in many countries leaving large amounts in temporary storage. Pu also remains as environmental contamination at various locations due to: accidents (e.g., Chernobyl, UKR; Thule, GRL); research and processing releases (e.g., Los Alamos, USA, Mayak, RUS); and former weapons testing (e.g., Nevada Test Site, USA; Semipalatinsk, KAZ; and Maralinga, AUS). We assessed the availability and uptake of Pu in a range of wildlife types at legacy sites with the focus on new data from outside of the remediation zone at the former Taranaki site, Maralinga, South Australia. Of key interest are the uptake and biokinetics of Pu in mammals, particularly from environmental exposure to the undetonated Pu-oxide forms at Taranaki that are representative of much of the worldwide inventory. Our results confirm that environmentally dispersed Pu can remain accessible for uptake by biota over decadal time scales. For example, after more than 50 years since deposition at Taranaki, 62% of Pu has remained in the 0-2 cm surface layer, and nearly 100% in the 0-10 cm of soil depths. Although a small fraction of the Pu is migrating downward at —0.2 cm per year, it appears that most Pu will continue to remain accessible into the future for plants and animals that inhabit the surface, or shallow soil layers. The uptake of Pu into terrestrial animals occurs mainly by inhalation and ingestion, and can be persistent over time as indicated by constant uptake rates for mammals, and a potential increase for reptiles, in data spanning 30 years. The rates of soil-to-animal transfer at Taranaki, align well with those from similar sites where undetonated Pu was tested (e.g., Nevada Test Site, US). However, the uptake values at these sites are lower than general world-wide values, likely due to the presence of less-absorbable forms of Pu. The importance of the physico-chemical form of the Pu on uptake was also seen in data from fish exposed to more absorbable forms of Pu in liquid discharge ponds near processing facilities in the US. These fish had two orders of magnitude higher uptake values than those for similar species receiving Pu solely from atmospheric fallout. The physico-chemical form of the Pu can also influence how it is distributed among mammalian organs. The relatively insoluble forms at Taranaki, which include particulates, led to elevated concentrations of unabsorbed Pu in the lung, gastrointestinal tract, and adhered to skin/fur of mammals. This elevated Pu can provide a secondary source during human, and ecological, food-chain consumption. Of the Pu that was absorbed within the body, much higher accumulation was measured in the skeleton, and much lower in the liver, in mammals at Taranaki as compared with the standard model of 50% skeleton, and 30% liver (ICRP 1986). Our data provides specific quantification of Pu uptake rates in wildlife and the subsequent accumulation in various mammalian organs. These will aid future assessments of the Maralinga site, as well as more general evaluations related to the low-solubility forms of Pu that make up a large share of the worldwide inventory.
- 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
- 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