This review provides a comprehensive evaluation of the state-of-knowledge of radiation effects in crystalline ceramics that may be used for the immobilization of high-level nuclear waste and plutonium. The current understanding of radiation damage processes, defect generation, microstructure development, theoretical methods, and experimental methods are reviewed. Fundamental scientific and technological issues that offer opportunities for research are identified. The most important issue is the need for an understanding of the radiation-induced structural changes at the atomic, microscopic, and macroscopic levels, and the effect of these changes on the release rates of radionuclides during corrosion.

With the increasing demand for the development of nuclear power comes the responsibility to address the issue of waste, including the technical challenges of immobilizing high-level nuclear wastes in stable solid forms for interim storage or disposition in geologic repositories. The immobilization of high-level nuclear wastes has been an active area of research and development for over 50 years. Borosilicate glasses and complex ceramic composites have been developed to meet many technical challenges and current needs, although regulatory issues, which vary widely from country to country, have yet to be resolved. Cooperative international programs to develop advanced proliferation-resistant nuclear technologies to close the nuclear fuel cycle and increase the efficiency of nuclear energy production might create new separation waste streams that could demand new concepts and materials for nuclear waste immobilization. This article reviews the current state-of-the-art understanding regarding the materials science of glasses and ceramics for the immobilization of highlevel nuclear waste and excess nuclear materials and discusses approaches to address new waste streams.

The room-temperature tetragonal-to-cubic transformation in BaTiO, powders with decreasing particle size has been carefully studied, using materials prepared mainly by hydrothermal methods. Hydrothermal BaTiO, powders exhibited a more uniform particle size distribution than oxalate-route powders, with X-ray diffraction and electron microscopy indicating that powders 50.19 pm in size were fully cubic while powders 20.27 pm were completely tetragonal (within a 5% detection limit for cubic material) at room temperature. The tetragonal-to-cubic transformation temperature was also found to lie in the range of 121" -C 3°C for BaTiO, powders with room-temperature (c/a) values > 1.008. No transformation could be detected using differential scanning calorimetry for BaTiO, particles with a (cla) c 1.008 at room temperature. BaTiO, powder with a particle size just too small (0.19 pm) to be tetragonal at room temperature remained cubic down to 80 K. Different models for the cubic-to-tetragonal room-temperature transformation are discussed. Hydroxyl ions do not appear to greatly affect the cubic-to-tetragonal transformation, which appears to be essentially dependent on particle size. It is concluded that a model based on surface free energy, as previously discussed for the monoclinic-to-tetragonal transformation at room temperature of fine ZrO, particles, is consistent with the experimental data.

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