Assessing doses to terrestrial wildlife at a radioactive waste disposal site: Inter-comparison of modelling approaches

Abstract

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.

Solution Speciation of Plutonium and Americium at an Australian Legacy Radioactive Waste Disposal Site

“…From 1960 to 1968, the site was used for the disposal of low-level radioactive solid and liquid wastes generated at the Lucas Heights research facility during activities of the Australian Atomic Energy Commission (AAEC). , Since the cessation of disposal operations in 1968, the site has been maintained and monitored by the AAEC and its successor, the Australian Nuclear Science and Technology Organisation (ANSTO). Because of the range of research activities undertaken at the time, the buried wastes contained a variety of radionuclides including 3 H, 60 Co, 90 Sr, 137 Cs, 232 Th, and 235,238 U, as well as over a tonne of beryllium. , To assess the environmental impact and the selection of possible management strategies for the LFBG, the distribution and behavior of radioactive contamination at the site is being investigated. − …”

“…A specific concern at the LFBG is the presence of transuranic nuclides including plutonium ( 239,240 Pu) and americium ( 241 Am). , Although the amount of Pu and Am is reported to be small (several grams of Pu in total and a similar activity of Am), the presence of these long-lived alpha-emitters in the buried wastes motivates investigation of their potential impacts on natural and human environments, including animals and plants that utilize the site, local rivers and creeks (Figure b), and developing residential areas within a few kilometers of the LFBG . Therefore, there is a need to understand the status of radioactive contamination at the site.…”

Radiation Dose Assessment Model for Terrestrial Flora and Fauna and Its Application to the Environment near Fukushima Accident

“…The models for predicting the radiation dose for terrestrial flora and fauna were comprehensively studied through the exposure scenario test for the wildlife within the Chernobyl exclusion zone in the biota working group of the IAEA/EMRAS project [6]. In addition, a comparison study of various models was conducted for assessing the doses to wild flora and fauna at a radioactive waste disposal site in Australia [7]. The models used in the studies were all based on the equilibrium concentration ratio (CR) model.…”

Predicting exposure of wildlife in radionuclide contaminated wetland ecosystems

“…Within these programmes biota dose model inter-comparisons were performed for terrestrial Johansen et al, 2012), and freshwater lake ecosystems (Yankovich et al, 2010;IAEA, in press). These studies showed that model results can vary by up to three orders of magnitude in dose predictions Johansen et al, 2012), with most variation attributed to modelled uptake of radionuclides by organisms. To help refine the models, further inter-comparison exercises were recommended , especially for those exposure scenarios not specifically considered in available models and radionuclide-organism combinations not yet assessed.…”