Browsing by Author "Hutton, Tanya"

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    Challenges facing the development of new nuclear capacity in South Africa
    (2024) Makhubela, Thomas; Hutton, Tanya
    South Africa currently (2022) hosts two nuclear reactor facilities, the electricity generating Koeberg nuclear power plant, and the SAFARI - 1 reactor, which is used for medical isotope production, research, and development. With the nationwide problems of loadshedding due to a lack of operational capacity, resulting in economic decline, and the climate concerns associated with fossil fuels, the addition of nuclear capacity is an appealing concept. This dissertation details several of the challenges associated with the development of new nuclear power plants (NPPs) in South Africa, from the availability of nuclear fuel and technical expertise to environmental, political, and economic issues. These challenges were explored in both national and international spheres, drawing on case studies from around the world. The long-term operation of the existing nuclear capacity was considered, alongside the viability of spent nuclear fuel re-processing in the South African context as a strategy for waste management and generation of revenue. Ultimately, political factors, and public participation and acceptance were identified as the primary challenges that have delayed the deployment of NPPs, which need to be addressed by the government when developing a rigid national nuclear energy policy to sustain South Africa's economy both for current and future generations.
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    Moderation of high-energy fast neutrons in beryllium from a tokamak fusion reactor and heat transfer to the cooling water system
    (2020) Ellis, Benjamin; Leadbeater, Thomas; Hutton, Tanya
    A modeling demonstration of the moderation of 14.1 MeV primary neutrons in beryllium emitted from a D-T fusion nuclear reaction. The energy deposited from neutron-beryllium interactions which produces heat in the blanket of a fusion tokamak. A review of literature and data available for neutron-beryllium interactions is provided to support the MC software of a simplified model of the ITER first wall and blanket. Energy deposited in regions of the model using FLUKA are used to calculate a polynomial heat flux profile through the model. One dimensional conductive heat transfer through the model is performed and the cooling capacity of the coolant channels via convective heat transfer is explored.
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    Towards measuring the relative biological effectiveness of high-energy neutrons at iThemba LABS
    (2025) Fairall, Elizabeth; Buffler, Andrew; Hutton, Tanya
    In space, neutrons with energies of up to several TeV are produced through the interac-tions of primary cosmic radiation with matter such as in spacecraft shielding, and in the atmospheres and regoliths of moons and planets. The development of radiation health-risk models for space exploration requires the quantification of the biological effects of neutrons, and in the current radiation protection framework this is achieved via measure-ments of the neutron Relative Biological Effectiveness (RBE). The current deficiency of experimental data regarding the biological effects of high-energy neutrons calls for dedi-cated RBE experiments at neutron energies greater than 20 MeV for the doses, dose rates, and biological endpoints that are relevant to space travel. This project aimed to identify key knowledge gaps and improve neutron radiation risk estimates by developing a stan-dardised approach to measure the limiting maximum value of neutron RBE at low doses (RBEM) at the iThemba Laboratories for Accelerator Based Sciences (LABS) high-energy neutron facility. Data from a preparatory experiment conducted with neutrons produced by a 66.48 MeV proton beam irradiating an 8.0 mm lithium target are used to illustrate the metrological methods for the characterisation of the neutron beam energy distribution and fluence at the iThemba LABS high-energy neutron facility. The metrological characterisation was combined with Monte Carlo radiation transport simulations to establish the absorbed dose delivered to vials containing human peripheral blood mononuclear cells that were irradiated during the experiment. The dosimetry results were related to the correspond-ing observed yield of γ-H2AX foci in the irradiated samples, to obtain dose-response relationships with linear yield coefficients of 10.12 ± 0.63 Gy−1 and 7.45 ± 0.66 Gy−1 for irradiations with neutrons with fluence-weighted average energies of 40.11 ± 0.92 MeV and 37.26 ± 0.40 MeV respectively. The results of this analysis were used to make recom-mendations for future neutron RBE measurements at iThemba LABS at energies relevant to space travel. Such measurements require reliable neutron beam metrology and detailed computational simulations of the experimental setup for both the neutron and reference irradiations, along with appropriate radiobiological analyses.
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    Validation and verification of FLUKA for neutron shielding problems
    (2022) Dondolo, Petrus; Hutton, Tanya; Leadbeater, Thomas
    Monte Carlo-based radiation transport codes provide an opportunity to simulate situations with various levels of activation and different induced nuclides. However, to test their reliability, it is important to verify the simulation codes by comparing them with experimental data. In this study, validation of simulation models with experiments was performed with the purpose of determining the reliability of the simulation/experimental results. Concrete is the most generally used shield material as it is inexpensive and adjustable for any construction design. Radiation shielding properties of concrete may vary depending on the concrete composites. In this thesis, the fluences (i.e. the flux integrated over time) of neutrons impinging on the shielding nuclear material were studied using FLUKA Monte Carlo package. The rectangular blocks of shielding nuclear materials such as concrete ingredients: cement, sand and water were irradiated with a beam of 14 MeV neutrons and the shielding properties of these materials were investigated using FLUKA Monte Carlo simulation code. The simulation set-up replicates the experimental measurements performed within the nuclear laboratory in the Department of Physics at the University of Cape Town. The comparison of the effective removal cross-section shows a good agreement between experiments and FLUKA. The results from these two approaches show general agreement for sand and cement, but show some minor deviations for water and concrete. The source of these deviations is discussed, along with potential solutions. FLUKA has been well benchmarked and validated against other Monte Carlo codes. The discrepancies obtained on water and concrete may have occurred from the material properties in the input file. Comparisons of results are presented and the discrepancies and agreements between the two methods are discussed for these target materials. The effective removal cross section of a concrete mix was measured by simulation to be 0.1038 +/- 0.0005 cm-1 and by experiment to be 0.1230 +/- 0.0002 cm-1 of 14 MeV neutrons. This illustrates a broad agreement between experiment and simulation in the case of concrete ingredients. Validation and comparison of measured and simulated neutron irradiation on concrete ingredients shows good agreement, supporting the use of FLUKA for estimating the neutron transmission into the shielding material.