Study of Structural and Strength Changes in Lithium-Containing Ceramics-Potential Blanket Materials for Nuclear Power, Subjected to High-Dose Proton Irradiation

The paper considers the hydrogenation processes in Li₂TiO₃ ceramics under irradiation with protons with an energy of 500 keV and fluences of 1 × 10¹⁰-5 × 10¹⁷ ion/cm². The choice of the type of irradiation, as well as the irradiation fluences, is based on the possibilities of modeling hydrogenation processes and studying the kinetics of structural changes caused by the accumulation of radiation damage. The choice of Li₂TiO₃ ceramics as objects of research is due to their prospects for using as blanket materials of thermonuclear reactors for the tritium production and accumulation. It was found that the formation of point defects and their subsequent evolution associated with the formation of complex compounds and the filling of pores, followed by the formation of gas-filled bubbles, the presence of which leads to a decrease in crack resistance and resistance to destruction of the near-surface layer. Based on the data on structural changes and evolution of the crystal lattice parameters, its swelling, a description of the destruction processes associated with hydrogenation in Li₂TiO₃ ceramics was proposed. Also, during the studies, it was found that at irradiation fluences above 1 × 10¹⁷ ion/cm², the appearance of impurity inclusions characteristic of the TiO₂ phase was observed, the presence of which indicates the crystal lattice destruction processes because of accumulation of radiation damage and deformations caused by them. Critical doses are established at which there is a sharp deterioration in strength and crack resistance, reflecting the resistance of ceramics to mechanical external influences.

Synthesis, Phase Transformations and Strength Properties of Nanostructured (1 - x)ZrO2 - xCeO2 Composite Ceramics

The aim of this work is to study the properties of nanostructured (1 − x)ZrO₂ − xCeO₂ composite ceramics, depending on the content of oxide components, as well as to establish the relationship between the phase composition of ceramics and strength properties. The choice of (1− x)ZrO₂ − xCeO₂ composite ceramics as objects of study is due to the great prospects for using them as the basis for inert matrix materials for nuclear dispersed fuel, which can replace traditional uranium fuel in high-temperature nuclear reactors. Using X-ray diffraction, it was found that the variation of the oxide components leads to phase transformations of the Monoclinic-ZrO₂ → Monoclinic − Zr_0.98Ce_0.02O₂/Tetragonal − ZrO₂ → Tetragonal − Zr_0.85Ce_0.15O₂ → Tetragonal − ZrCeO₄/Ce_0.1Zr_0.9O₂ type. As a result of mechanical tests, it was found that the formation of tetragonal phases in the structure of ceramics leads to strengthening of ceramics and an increase in crack resistance, which is due not only to an increase in the crystallinity degree, but also to the effect of dislocation hardening associated with a decrease in grain size. It has been established that a change in the phase composition due to phase transformations and displacement of the ZrO₂ phase from the ceramic structure with its transformation into the phase of partial replacement of Zr_0.85Ce_0.15O₂ or Ce_0.1Zr_0.9O₂ leads to the strengthening of ceramics by more than 3.5–4 times. The results of resistance to crack formation under single compression showed that the formation of the ZrCeO₄ phase in the structure of ceramics leads to an increase in the resistance of ceramics to cracking by more than 2.5 times.

Study of Degradation Mechanisms of Strength and Thermal-Physical Properties of Nitride and Carbide Ceramics-Promising Materials for Nuclear Energy

The dependences of changes in the strength properties of nitride and carbide ceramics under high temperature irradiation with Kr¹⁵⁺ and Xe²²⁺ heavy ions at irradiation doses of 10¹²-10¹⁵ ions/cm² are presented in this work. The irradiation was chosen to simulate radiation damage processes that are closest to the real conditions of reactor tests in operating modes of increased temperatures. Polycrystalline ceramics based on AlN, Si₃N₄ nitrides, and SiC carbides were chosen as objects of research, as they have great prospects for use as a basis for structural materials for high-temperature nuclear reactors, as well as materials for nuclear waste disposal. During these studies the effect of radiation damage caused by irradiation with different fluences on the change in mechanical strength and hardness were determined, and the mechanisms causing these changes depending on the type of irradiated materials were proposed. The novelty of this study is in the results obtained determining the stability of the strength and thermophysical parameters of nitride and carbide ceramics exposed to high-temperature irradiation, which made it possible to determine the main stages and mechanisms for changing these parameters depending on the accumulated radiation damage. The relevance of this study consists not only in obtaining new data on the properties of structural materials exposed to ionizing radiation, but also in the possibility of determining the mechanisms of radiation damage in ceramics.