Thesis Abstracts 2001
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Polymeric Radioactive Waste Disposal Containers
By: Lieutenant (Navy) Michael Walker
Abstract
The research carried out in Canada in the design of containers for the disposal of radioactive waste has focussed on spent nuclear fuel, even though the quantities of other currently stored radioactive wastes are substantially greater. Research carried out at the Royal Military College of Canada on the effects of mixed fields of radiation on high polymer adhesives and composite materials has shown that some polymers are quite resistant to radiation and could well serve in the fabrication of radioactive waste disposal containers.
The purpose of this research was to determine if thermoplastic polymers could be used as superior materials to replace metals in the application of low and intermediate level radioactive waste disposal containers. Polymers have the advantage that they do not corrode like metals. The experimental methods, used in this research, focused on the effects of radiation on the properties of the materials. Polypropylene, Nylon 66, Polycarbonate, and Polyurethane, with and without glass fibre reinforcement, were studied. The method involved irradiating injection moulded tensile test bars with the SLOWPOKE-2 reactor to accumulate doses ranging from 0.5 to 6.0 MGy. To determine the effects of the various doses on the materials, Density, Tensile, Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM) tests were run.
For each polymer, the test methods supported predominant crosslinking of polymeric chains severed by radiation. This was evident from observed changes in the mechanical and chemical properties of the polymers, typical of crosslinking. The mechanical changes included an overall increase in density, an increase in Young's modulus, a decrease in strain at break, and only minor changes in strength. The chemical changes included differences in chemical transition temperatures characteristic of radiation damage. The test methods also evidenced minor radiation degradation at the fibre/matrix interfaces in the glass fibre reinforced polymers. Based on these results, any of the investigated polymers could potentially be used for disposal containers due to their abilities to adequately resist radiation. The last part of this thesis provides a potential design framework for low and intermediate level radioactive waste disposal containers.
