Combined effects of temperature, chemical and radiation exposure on the diffusion and mechanical properties of polyamide 6,6 and its semi-aromatic copolymer: An investigation into the failure mechanisms of polymeric materials used as storage containers for radioactive waste.

摘要

As part of the quest to find a solution for the disposal of Canada's radioactive waste, researchers at the Royal Military College of Canada have conducted research on the use of polymer-based composite materials for the storage of radioactive wastes. Previous work had determined that several of these materials exhibit the required mechanical strength and radiation resistance to make them viable alternatives to the titanium alloys currently proposed by Atomic Energy Canada Ltd. (AECL) for the fabrication of waste containers as per the Environmental Impact Statement on the Concept of Disposal of Canada's Nuclear Fuel Waste.; An evaluation of the performance of polymeric materials after exposure to radiation and acidic aqueous solutions provides a basis for the evaluation of failure mechanisms affecting these materials. The work completed in this thesis evaluated the importance of the combined effects of aqueous solution diffusion, radiation exposure, and temperature on the mechanical performance, diffusion profile and molecular structure of polymeric materials.; Nylon 6,6 is a polymeric material that is highly hydrophilic, susceptible to hydrolysis, and capable of absorbing large amounts of solution (>9% by weight) in short periods of time. The presence of the aromatic component monomer within the Semi-Aromatic Nylon 6,6 Copolymer results in a drop in the maximum solution uptake to approximately 5% and a reduction in the material's susceptibility to hydrolysis. The diffusion profiles for Nylon 6,6 and Semi-Aromatic Nylon 6,6 Copolymer were studied for samples saturated at temperatures ranging from 20 to 90°C in solutions of decreasing pH from distilled water to 1.0M sulfuric acid.; Neutron Activation Analysis was used as a novel analytical technique to evaluate the sulfur content within the saturated samples as a function of the diffusion time. As diffusion time progressed, the sulfur content within the sample continued to rise to a level where the acid/water molar ratio was much higher (7 to 8 times) in the sample than that in the bulk. This resulted in a marked decrease in mechanical performance after the diffusion process was complete.; The extent of degradation was evaluated via changes in mechanical performance, stress at yield and flexural modulus, and inherent viscosity. Nylon 6,6 samples typically displayed a reduction in both stress at yield and flexural modulus of approximately 75% after saturation with distilled water and 80% after saturation with 1.0M sulfuric acid, for a saturation temperature of 20°C. An increase in saturation temperature resulted in a further decrease in mechanical performance for Nylon 6,6 for higher acid concentration saturation solutions, resulting in up to 90% reduction for 1.0M sulfuric acid saturation at 60°C. (Abstract shortened by UMI.)