Comparative analysis of different fidelity fuel performance models for fuel temperature predictions

Thermal-hydraulics subchannel models have proven to give an acceptable compromise between modeling fidelity and computational efficiency in coupled multi-physics steady state, depletion, and transient calculations. The accuracy in modeling both gas-gap conductance and fuel thermal conductivity is of significant importance for fuel temperature prediction, which, in turn, is crucial for calculation of Doppler feedback on power. A comparative analysis of fuel performance models of different fidelity was performed using the sub-channel code CTF, and the higher fidelity fuel performance codes FRAPCON and BISON. The purpose of this study was to ascertain the predictive accuracy of the informed fuel rod model in CTF, thus the potential to inform this model using data from higher fidelity fuel performance models. Excellent agreement was found between CTF and FRAPCON, and between CTF and BISON with respect to inside clad temperature as well as to fuel surface and fuel centerline temperatures when the CTF gap conductance was set to the BISON and FRAPCON calculated gap conductance values. With respect to the CTF and FRAPCON comparison, the maximum temperature difference between the two codes for a given power level and burnup value was below 2 degree Kelvin for clad inner surface and fuel surface temperature. For fuel centerline temperature, the maximum temperature difference was found to be below 7 degree Kelvin at the highest power level and burnup value. Similarly, the CTF and BISON comparison resulted in maximum temperature differences less than 5 degree Kelvin for the fuel centerline temperature. These results demonstrate that, if the gap conductance, dimensions, and radial power distribution is correctly set in CTF, the CTF-predicted rod temperature distribution will match closely with higher fidelity tools and licensed industry level fuel performance codes for normal operating conditions.