The application of image-analytical, indenting, and quantitative scanning electron microscopic methods on irradiated uranium and mixed-oxide fuel materials yields nonlinear thermodynamic operational data. Any oxide fuel material from a specific fabrication process undergoes its own means of transformation toward thermodynamic equilibrium through structural metamorphoses by irreversible processes far from equilibrium. The related dissipation energies vary with burnup and temperature because of the variable capability of energy storage, due to specific structural reactions on nuclear impacts. This fact leads to a large variety of operational material properties. Preferable operational hyperelasticity and subsequent viscoelasticity can be predetermined by intentional selected kinetic processing during fuel fabrication.