Radiation and thermal effects on zeolites, smectites and crystalline silicotitanates.

摘要

Long-term radiation and thermal effects on materials in the near-field of a nuclear waste repository have been evaluated using accelerated laboratory experiments by energetic electron or ion beam irradiations. The materials studied include: zeolites, smectites, and crystalline silicotitanates (CST).; In situ transmission electron microscopy (TEM) during irradiation by 200 keV electrons has shown that all of the studied materials are susceptible to radiation-induced amorphization. At room temperature, complete amorphization was observed after ionizing doses of 1010∼10 12 Gy or displacement doses of ∼0.1 dpa. The critical amorphization dose increased with temperature for CST. A peak amorphization dose was found at ∼400°C for the smectites. A new experimental approach was developed using a combination of proton irradiation, TEM, and electron microprobe analysis techniques to overcome the difficulties in studying the chemical properties in the radiation-damaged region. A clear correlation between the structural damage and changes in ion-exchange and desorption capacities has been established for zeolite-Y, which maybe useful for predicting the long-term behavior of the near-field materials in a nuclear waste repository. Radiation-induced decrease in the release rate of radionuclides has been observed for the first time in the damaged materials, indicating that the structural damage in near-field materials may be beneficial for retarding the release of radionuclides from geologic disposal repository into biosphere. Possible mechanisms for radiation-induced changes in structure, ion exchange and desorption capacities have been proposed.