APPLICATION OF POLYMERS FOR THE LONG-TERM STORAGE AND DISPOSAL OF LOW- AND INTERMEDIATE-LEVEL RADIOACTIVE WASTE

摘要

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. A research program was launched to investigate the possibilities of using advanced polymers and polymer-based composites for high-level radioactive waste management on one hand and for intermediate- and low-level radioactive waste disposal on the other hand. Research was thus conducted in parallel on both fronts, and the findings for the later phase are presented. Thermoplastic polymers were studied for this application because they are superior materials, having the advantage over metals of not corroding and of displaying high resistance to chemical aggression. The experimental methods used in this research focused on determining the effects of radiation on the properties of the materials considered: polypropylene, nylon 66, polycarbonate, and polyurethane, with and without glass fiber reinforcement. The method involved submitting injection-molded tensile test bars to the mixed radiation field generated by the SLOWPOKE-2 nuclear reactor at the Royal Military College of Canada to accumulate doses ranging from 0.5 to 3.0 MGy. The physical, mechanical, and chemical effects of the various radiation doses on the materials were measured from density, tensile, differential scanning calorimetry, and scanning electron microscopy tests. For each polymer, the test results evidenced predominant cross-linking of the polymeric chains severed by radiation. This was evident from observed changes in the mechanical and chemical properties of the polymers, typical of cross-linking. The mechanical changes observed 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. All the changes in these properties are characteristic of the cross-linking phenomenon. For the glass-fiber-reinforced polymers, the results of the tests evidenced minor radiation degradation at the fiber/matrix interfaces. Based on these results, any of the investigated polymers could potentially be used for disposal containers due to their abilities to adequately resist radiation. This allowed proceeding one step further into determining a potential design framework for containers for the long-term storage and disposal of low- and intermediate-level radioactive waste.