The inherent radioactivity and heterogeneous microstructures of nuclear materials and fuels make them challenging research and engineering targets. Advanced light sources have enabled significant underpinning scientific contributions to the current understanding of structural and fuel cladding material microstructure and properties, as well as the development of structure-property relationships. These facilities could potentially help advance Department of Energy Office of Nuclear Energy (DOE-NE) mission priorities by enabling an underpinning understanding of technically important challenges such as irradiation-induced embrittlement and swelling, stress corrosion cracking and corrosion in extreme environments, reactor pressure vessel (RPV) steel aging, nuclear fuel characterization, and nuclear waste form optimization, and they could play a major role in the development of a material performance matrix to aid in designing new materials to meet the needs of advanced reactor concepts. However, delivery of an underpinning understanding is the mission of the DOE Office of Science (DOE-SC). While filling such knowledge gaps is important, efforts in this direction should not be confused with DOE-NE's strategic, technology-focused mission goals of enabling the continued operation of existing U.S. nuclear reactors, supporting the deployment of advanced nuclear reactors, developing advanced nuclear fuel cycles, and maintaining U.S. leadership in nuclear energy technology.