An alternate thermal-mechanical behavior model for cracked UO2 pelletized fuel is presented. It is recognized that fuel cracking and relocation cause some of the initial pellet-cladding gap (the “free area”) to be moved into the fuel in the form of cracks. The introduction of this free area into the fuel causes the fuel effective thermal conductivity and effective elastic moduli to be simultaneously reduced to values significantly less than laboratory data for solid pellets. Hooke’s Law and a crack compliance model are used to deduce the effective fuel conductivity and moduli from simultaneous in-reactor measurements of rod power, fuel center temperature, and cladding elongation. The fuel-cladding “gap” is considered as another “crack,” and is also described by the crack compliance model, which predicts that there is always some finite amount of fuel-cladding contact. The primary thermal mechanical feedback mechanism is found to be due to crack closure effects on fuel effective thermal conductivity, rather than gap closure effects on gap conductance.