Australian Uranium and NORM: Ecological Transfer to Native Vegetation Within the Arid Zone and UOC Phase Analysis Using Variable Temperature Synchrotron-XRD

Author: Samantha Pandelus

Pandelus, Samantha, 2022 Australian Uranium and NORM: Ecological Transfer to Native Vegetation Within the Arid Zone and UOC Phase Analysis Using Variable Temperature Synchrotron-XRD, Flinders University, College of Science and Engineering

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Understanding uranium and naturally occurring radioactive materials (NORM) in a radioecology and nuclear forensic context is critical for protecting the environment and nuclear security.

Environmental risk assessments for radiological contamination follow internationally accepted methods including the ‘Environmental Risk from Ionising Contaminants: Assessment and Management’ (ERICA) tool. However, these assessment tools lack the necessary reference data for Australian native species, within an arid environment. The understanding of radionuclide uptake in biota is also an area of increasing interest due to the ICRP recommendations to demonstrate protection of the environment. This research provides activity concentrations of 238U, 235U and 232Th chain radionuclides in soil and native vegetation from the arid Australian environment from two distinct locations, Olympic Dam and the Flinders Ranges Region. Both sites offer vastly different conditions when considering the natural geology, background radiation and surface operations. This research provides site specific concentration ratio (CR) datasets for shrubs and grasses for use within the ERICA tool to increase the confidence of Australian environmental impact assessments. The CRs calculated for the Olympic Dam region vary significantly from the CRs in the wildlife transfer database (WTD), however, the CRs from the Flinders Ranges region are in good agreement with the WTD.

In order to increase Australia’s nuclear security, extensive characterisation of nuclear materials must be performed. Uranium ore concentrate (UOC) is the final stage of Australian involvement within the nuclear fuel cycle. Therefore, UOCs are a focus for nuclear forensics regarding Australian uranium. The chemical speciation of uranium oxides is sensitive to the provenance of the samples and their storage conditions. Here, we use diffraction methods to characterize the phases found in three aged (>10 years) uranium ore concentrates of different origins as well as in situ analysis of the thermally induced structural transitions of these materials. The structures of the crystalline phases found in the three samples have been refined, using high-resolution synchrotron X-ray diffraction data. Rietveld analysis of the samples from the Olympic Dam and Ranger uranium mines has revealed the presence of crystalline α-UO2(OH)2, together with metaschoepite (UO2)4O(OH)6 5H2O, in the aged U3O8 samples, and it is speculated that this forms as a consequence of the corrosion of U3O8 in the presence of metaschoepite. The third sample, from the Beverley uranium mine, contains the peroxide [UO2(η2-O2)(H2O)2] (metastudtite) together with α-UO2(OH)2 and metaschoepite. A core−shell model is proposed to account for the broadening of the diffraction peaks of the U3O8 evident in the samples. This thesis will also establish the profile of Australian UOC phase analysis to increase the confidence for nuclear security relating to Australian produced uranium.

Keywords: radionuclide, radioecology, UOC

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2022
School: College of Science and Engineering
Supervisor: Allan Pring