This paper presents the quantification of uncertainty of the calculated temperature data for the Advanced Gas Reactor (AGR) fuel irradiation experiments conducted in the Advanced Test Reactor at Idaho National Laboratory in support of the Advanced Reactor Technologies Fuel Development and Qualification Program. The predicted temperatures with associated uncertainty for AGR tests using the ABAQUS finite element heat transfer code are used to validate the fission product transport and fuel performance simulation models. To quantify the uncertainty of calculated temperatures, this study identifies and analyzes model parameters of potential importance to the predicted fuel temperatures. The selection of input parameters for uncertainty quantification is based on the ranking of their influence on the variation of temperature predictions. Thus, selected input parameters include those with high sensitivity and those with large uncertainty. The propagation of model parameter uncertainty and sensitivity is then used to quantify the overall uncertainty of the calculated temperatures. The sensitivity analysis performed in this work went beyond the traditional local sensitivity. Using an experimental design, an analysis of pairwise interactions of model parameters was performed to establish the sufficiency of the first-order (linear) expansion terms in constructing the response surface. To achieve completeness, the uncertainty propagation made use of pairwise noise correlations of model parameters. The AGR-2 overall fuel temperature uncertainties reported here are less than 5% (or 60°C).