Review of recent experimental results on the behavior of actinide-bearing oxides and related materials in extreme environments

Oxide materials find use throughout the nuclear fuel cycle, from actinide-bearing ores and commercial reactor fuels to wasteforms for radionuclide disposal. In geological, reactor, and waste repository conditions, these materials are often exposed to ionizing radiation, high temperatures, and mechanical stresses. Recently, a large body of work has investigated the response of actinide oxides and analogue compounds to extreme environments, including the individual and combined effects of radiation, temperature, and pressure. Study of the phase behavior of these materials under such conditions can lead to improved understanding of their stability throughout the nuclear fuel cycle, as well as strategies for the mitigation of associated performance degradation. This article reviews some recent experimental work on this topic, highlighting advanced techniques developed for the exposure of materials to extreme environments, and for the in situ characterization of their structural and chemical responses. The study of two classes of nuclear materials is reviewed: binary oxides typical of nuclear fuels, and complex oxides typical of geological materials and wasteforms. Particular emphasis is placed on the individual and combined effects of modifications to the atomic and electronic structures of materials by exposure to extreme environments.