Effects of Ionising Radiation on Nuclear Materials

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Abstract

The prediction of energy loss properties and track structure effects of ionising radiation in materials is of importance to many areas of science, healthcare and technology, especially the nuclear industry. This study examines three different aspects of the electronic effects of ionising radiation on solid materials: the calculation of inelastic cross sections, the measurement of charge state fractions of ions through materials, and the radiolytic hydrogen produced from slurries under gamma irradiation.Predicting how ionising radiation will interact with matter often utilises collision cross sections for the interaction process. The electronic energy loss cross sections of ions in materials are predicted using a novel formalism requiring only the dipole oscillator strength distribution (DOSD) of the material of interest. DOSDs are constructed for silicon carbide and various oxides of interest to the nuclear industry. Electronic collision cross sections as well as average energy loss properties for incident protons, helium and other ions are calculated using the developed formalism. The formalism is shown to predict macroscopic energy loss properties well, especially at higher energies, suggesting the formalism is an acceptable simple yet elegant method for calculating electronic cross sections for use in Monte Carlo simulations of radiation track structures.The charge of an ion in a material affects the rate of energy loss during the passage through that material. The charge state fractions of lithium and helium ions in several metallic materials pertinent to the nuclear industry are measured and compared in order to improve the understanding of ion charge states in a radiation track structure. The new charge state fraction measurements show a clear dependence on material properties which appears to correlate with the ionisation potential of the material; however, a full understanding of the dependence is lacking.Radiolytic hydrogen production is of importance when considering the safety of spent nuclear material in cooling ponds and after disposal. One proposed clad coating for accident tolerant fuel currently under investigation is silicon carbide however its radiation chemistry is relatively unknown. The hydrogen produced from gamma-irradiated silicon carbide water slurries is investigated. The measured yield of H2 produced is greater than would be expected from a mixture rule. This excess production of H2 is believed to be due to transfer of energy from the solid ceramic to the aqueous phase by either low energy electrons or exciton dissociation at the water-carbide interface.These three areas of investigation are complementary aspects of the interaction of ionising radiation with solid material and add to the knowledge base necessary for an acceptable risk-based justification for sustainable energy production by nuclear fission power plants.

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