Investigation into the application of polyetherimide to nuclear waste storage containers.

摘要

The recent decision of the Canadian government to adopt deep geological waste storage as a solution to the high level radioactive waste management in the country has spurred much research into potential waste storage container designs. Although no final design has been chosen, the copper shell packed particulate container remains the most likely candidate for this application. The purpose of this research has been to conclude whether pure polyetherimide (PEI) or 30% glass fiber reinforced polyetherimide (30%GF PEI) would represent suitable alternative materials for the construction of such a container.;Based on the above mentioned results, is can be concluded that both pure and 30% GF PEI represent ideal candidates for the construction for waste storage containers to house high level radioactive waste. The excellent radiation, thermal and acid resistance of these materials as well as their low permeability to water and light weight coupled with high strength are indicators of the potential and versatility of this material to application in the nuclear field.;In order to determine this, the diffusion properties of the material were assessed as well as its resistance to radiation and elevated temperatures. Diffusion testing was done in sulphuric acid solutions at temperatures of 27, 40 and 60°C and concentrations of 1, 0.5, 0.1 mol kg-1 and 0 mol kg-1. Diffusion testing of both materials has shown their low permeability to water demonstrated by a maximal equilibrium weight gain of water of 1.123 ± 0.002 weight % (for 60°C and 0.1 mol kg -1 ) for pure PEI and of 0.654% ± 0.0002% for 30% GF PEI at 60°C in a solution of 0 mol kg-1 of sulphuric acid. In addition to this, modeling using COMSOL software was performed to calculate the diffusion coefficient and activation energy of the diffusion reaction. Both values indicate that the diffusion reaction is not spontaneous or favored and requires an input of energy to occur. Finally, the comparison of the COMSOL generated diffusion curves to the experimental data has shown that the water molecules do not penetrate the bulk of the material and that the diffusion reaction is in fact a sorption-desorption reaction occurring in the outer layers of the polymer. Flexural testing following diffusion testing until equilibrium showed no variation in flexural modulus caused by long term immersion in sulphuric acid solutions up to 1 mol kg-1 and temperatures up to 60 °C. SEM imaging of the samples showed degradation of the surface of the samples by acid, this effect was more pronounced with the 30% GF PEI samples. Using the SLOWPOKE-2 reactor at the Royal Military College of Canada, samples of pure and 30% GF PEI were irradiated at temperatures from pool temperature (15-20°C) to 60°C and doses from 0.5 MGy to 2 MGy. Following their irradiation, the changes in the mechanical properties of the samples were measured using the three point bend test. No significant changes in flexural modulus were measured. Following this, FTIR ATR was performed on the samples; the spectra of the irradiated samples displayed no variations from that of the unirradiated materials. Finally, a preliminary design of the container using buckling as the design criterion was performed, the container design consists of a 30% GF PEI cylinder 2.25 meter high with an internal radius of 0.31 meters and a thickness of 17.8 mm or a pure PEI cylinder 2.25 meter high with and internal radius of 0.31 meter and a thickness of 24.4 mm.