Browsing by Author "Keum, DK"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Assessing doses to terrestrial wildlife at a radioactive waste disposal site: Inter-comparison of modelling approaches
    (Elsevier Science BV, 2012-06-15) Johansen, MP; Barnett, CL; Beresford, NA; Brown, JE; Černe, M; Howard, BJ; Kamboj, S; Keum, DK; Smodiš, B; Twining, JR; Vandenhove, H; Vives i Batlle, J; Wood, MD; Yu, C
    Radiological doses to terrestrial wildlife were examined in this model inter-comparison study that emphasised factors causing variability in dose estimation. The study participants used varying modelling approaches and information sources to estimate dose rates and tissue concentrations for a range of biota types exposed to soil contamination at a shallow radionuclide waste burial site in Australia. Results indicated that the dominant factor causing variation in dose rate estimates (up to three orders of magnitude on mean total dose rates) was the soil-to-organism transfer of radionuclides that included variation in transfer parameter values as well as transfer calculation methods. Additional variation was associated with other modelling factors including: how participants conceptualised and modelled the exposure configurations (two orders of magnitude); which progeny to include with the parent radionuclide (typically less than one order of magnitude); and dose calculation parameters, including radiation weighting factors and dose conversion coefficients (typically less than one order of magnitude). Probabilistic approaches to model parameterisation were used to encompass and describe variable model parameters and outcomes. The study confirms the need for continued evaluation of the underlying mechanisms governing soil-to-organism transfer of radionuclides to improve estimation of dose rates to terrestrial wildlife. The exposure pathways and configurations available in most current codes are limited when considering instances where organisms access subsurface contamination through rooting, burrowing, or using different localised waste areas as part of their habitual routines. Crown Copyright © 2012 Published by Elsevier B.V
  • Thumbnail Image
    Item
    Best practices for predictions of radionuclide activity concentrations and total absorbed dose rates to freshwater organisms exposed to uranium mining/milling
    (Elsevier, 2022-02) Goulet, R; Newsome, L; Vandenhove, H; Keum, DK; Horyna, J; Kamboj, S; Brown, JE; Johansen, MP; Twining, JR; Wood, MD; Černe, M; Beaugelin-Seiller, K; Beresford, NA
    Predictions of radionuclide dose rates to freshwater organisms can be used to evaluate the radiological environmental impacts of releases from uranium mining and milling projects. These predictions help inform decisions on the implementation of mitigation measures. The objective of this study was to identify how dose rate modelling could be improved to reduce uncertainty in predictions to non-human biota. For this purpose, we modelled the activity concentrations of 210Pb, 210Po, 226Ra, 230Th, and 238U downstream of uranium mines and mills in northern Saskatchewan, Canada, together with associated weighted absorbed dose rates for a freshwater food chain using measured activity concentrations in water and sediments. Differences in predictions of radionuclide activity concentrations occurred mainly from the different default partition coefficient and concentration ratio values from one model to another and including all or only some 238U decay daughters in the dose rate assessments. Consequently, we recommend a standardized best-practice approach to calculate weighted absorbed dose rates to freshwater biota whether a facility is at the planning, operating or decommissioned stage. At the initial planning stage, the best-practice approach recommend using conservative site-specific baseline activity concentrations in water, sediments and organisms and predict conservative incremental activity concentrations in these media by selecting concentration ratios based on species similarity and similar water quality conditions to reduce the uncertainty in dose rate calculations. At the operating and decommissioned stages, the best-practice approach recommends relying on measured activity concentrations in water, sediment, fish tissue and whole-body of small organisms to further reduce uncertainty in dose rate estimates. This approach would allow for more realistic but still conservative dose assessments when evaluating impacts from uranium mining projects and making decision on adequate controls of releases. © 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license.
  • Thumbnail Image
    Item
    Biota dose modelling: Little Forest Burial Ground scenario
    (Australian Nuclear Science and Technology Organisation, 2012-10-16) Johansen, MP; Barnett, CL; Beresford, NA; Brown, JE; Černe, M; Howard, BJ; Kamboj, S; Keum, DK; Payne, TE; Smodiš, B; Twining, JR; Vandehnove, H; Vives i Batlle, J; Wood, MD; Yankovich, TL; Yu, C
    Radiation doses to terrestrial wildlife were examined in a model inter-comparison study on a diverse range of terrestrial plants and animals at the Little Forest Burial Ground, NSW, Australia. This inter-comparison was one in a series conducted under the IAEA Environmental Modelling for Radiation Safety Programme (EMRAS), which indicated general agreement among available biota dose models in the use of dose conversion parameters for standard organisms and geometries. However, notable variation in dose estimates emerged when the models were applied to a terrestrial deposition scenario (Chernobyl exclusion zone, Ukraine); a freshwater aquatic scenario (Perch Lake, Canada; a low-level burial ground scenario (Little Forest Burial Ground, Australia;), as well as additional aquatic (Beaverlodge, Canada) and wetlands (various locations) scenarios currently underway. Given the range in outcomes from the various modelling approaches of the previous EMRAS studies, the Little Forest Burial Ground scenario focused on quantifying the factors causing variation. The dominant variable factor (up to orders of magnitude on mean total dose rates) was the soil-to-organism transfer of radionuclides. Additional variation was associated with: exposure configurations (two orders of magnitude when considering trees growing on the waste trenches); inclusion/exclusion of progeny in Th and U isotopes (typically less than one order of magnitude); and radiation weighting factors and dose conversion coefficients (typically less than one order of magnitude). At Little Forest, results suggest radionuclide uptake is occurring in wildlife, but at low levels as most organisms only access the relatively clean surface soils above the buried wastes. Doses to acacia tree were elevated, however, due to its deeper roots having direct access to the buried wastes, with predictions of 95th percentile doses above the screening levels indicating further study is warranted. Our study confirms and adds to the outcomes of previous EMRAS studies in quantifying the sources of variation in biota dose modelling, and highlights soil to-organism transfer as a key source of uncertainty. It prompts continued evaluation of the underlying mechanisms governing soil-to-organism transfer of radionuclides to improve estimation of dose rates to terrestrial wildlife.
  • Thumbnail Image
    Item
    Dose modelling comparison for terrestrial biota: IAEA EMRAS II Biota Working Group's Little Forest Burial Ground scenario
    (International Union of Radioecology, 2011-06-19) Johansen, MP; Barnett, CL; Beresford, NA; Brown, JE; Černe, M; Howard, BJ; Kamboj, S; Keum, DK; Smodiš, B; Twining, JR; Vandenhove, H; Vives i Batlle, J; Wood, MD; Yu, C
    Radiological doses to terrestrial biota have been examined in a model inter-comparison study that emphasised the identification of factors causing variability in dose estimation. Radiological dose rates were modelled for ten species representing a diverse range of terrestrial plant and animals with varying behavioural and physical attributes. Dose to these organisms may occur from a range of gamma (Co-60, Cs-137), beta (Sr-90) and alpha (Th-232, U-234 and U-238, Pu-238, Pu-239/240 and Am-241) emitting radionuclides. Whilst the study was based on a specific site - the Little Forest Burial Ground, New South Wales, and Australia - it was intended to be representative of conditions at sites throughout the world where low levels of radionuclides exist in soil due to waste disposal or similar activities.
  • No Thumbnail Available
    Item
    The estimation of absorbed dose rates for non-human biota: an extended inter-comparison
    (Springer, 2011-05-01) Vives i Batlle, J; Beaugelin-Seiller, K; Beresford, NA; Copplestone, D; Horyna, J; Hosseini, A; Johansen, MP; Kamboj, S; Keum, DK; Kurosawa, N; Newsome, L; Olysaegers, G; Vandenhove, H; Ryufuku, S; Lynch, SV; Wood, MD; Yu, C
    An exercise to compare 10 approaches for the calculation of unweighted whole-body absorbed dose rates was conducted for 74 radionuclides and five of the ICRP's Reference Animals and Plants, or RAPs (duck, frog, flatfish egg, rat and elongated earthworm), selected for this exercise to cover a range of body sizes, dimensions and exposure scenarios. Results were analysed using a non-parametric method requiring no specific hypotheses about the statistical distribution of data. The obtained unweighted absorbed dose rates for internal exposure compare well between the different approaches, with 70% of the results falling within a range of variation of +/- 20%. The variation is greater for external exposure, although 90% of the estimates are within an order of magnitude of one another. There are some discernible patterns where specific models over- or under-predicted. These are explained based on the methodological differences including number of daughter products included in the calculation of dose rate for a parent nuclide; source-target geometry; databases for discrete energy and yield of radionuclides; rounding errors in integration algorithms; and intrinsic differences in calculation methods. For certain radionuclides, these factors combine to generate systematic variations between approaches. Overall, the technique chosen to interpret the data enabled methodological differences in dosimetry calculations to be quantified and compared, allowing the identification of common issues between different approaches and providing greater assurance on the fundamental dose conversion coefficient approaches used in available models for assessing radiological effects to biota. © 2011, Springer.