A presentation is provided of the design features and measuring capabilities of a high pressure test rig used for study of mechanical aspects of fuel performance under simulated pressurized water reactor conditions. In-pile profilometry data on one small gap (55 μm) segment (SGS) and one large gap (170 μm) segment (LGS) show different trends with increasing burnup to 5.4 MWd/kg UO2 (end of test). Significant fuel-induced cladding deformations developed in the SGS during the startup ramp, including clear permanent circumferential ridge formations. During subsequent irradiation, only minor permanent dimensional changes were measured. The deformation behavior of the LGS was characterized by a reduction in the cladding average diameter and an increase in ovality with burnup (time). The highest rate of change for both quantities was observed at low burnup. A brief review of ten current Zircaloy creep correlations reveals a large spread in predictive capabilities.