Abstract: Diffraction is well suited to the characterization of microstructures. Neutron diffraction, in particular, has some undeniable advantages for studying activated samples. Neutrons penetrate millimeters into most materials, providing a statistically relevant probe of the microstructure in the bulk of the material. Moreover, little or no hazardous and costly sample preparation is necessary, which enables repeat tests on the same sample or even in-situ measurements under simulated operating conditions. Finally, neutron detectors are often insensitive to background gamma radiation emitted from activated samples. The SMARTS diffractometer at the Lujan Center was designed to study engineering materials under their operating conditions and, as such, has sophisticated sample environments enabling in-situ ND studies during deformation and at non-ambient temperatures. This talk will use the example of in-situ diffraction measurements during annealing and deformation of irradiated HT-9 steel to highlight the capabilities of the instrument, in particular, related to the study of activated materials.