Small fraction of high conductivity BeO in UO2 fuel significantly improves thermal conductivity and also affects the overall performance of the fuel during steady state operation and during transients. In this study, performance of UO2-BeO composite under transient conditions such as loss of coolant accident (LOCA), using FRAPTRAN (fuel rod analysis program transient), was carried out. The subroutines in FRAPTRAN code that calculate key thermophysical properties such as thermal conductivity, specific heat capacity, and specific enthalpy were modified to account for the presence of the BeO in UO2. The fuel performance parameters like gas gap pressure, energy stored in fuel, and temperature profiles were studied. The simulation results showed reductions in fuel centerline temperatures and lower temperature drop across fuel rod cross-section under normal fuel operations. It was observed that there was reduction in gas gap pressure and energy stored in fuel. Transient conditions involving cladding rupture were investigated and important performance parameters such as cladding strain were studied. During these transients, the addition of BeO to UO2 fuel seems beneficiary. 1. Introduction Commercial nuclear reactors use uranium oxide, UO2, as a nuclear fuel. It is being used as a common nuclear fuel due to ease in its fabrication and good performance. However, it has a low thermal conductivity in the range of 2–8？W-m/K for temperature range from room temperature to 1000°C with decreasing value at high temperatures. There are efforts to increase its thermal conductivity by addition of compounds like BeO [1] and SiC. UO2-BeO composite has better temperature stability when compared to UO2-SiC. Many studies have been taken up to study the performance UO2-BeO fuel. The BeO is chosen as high thermal conductivity material in UO2 because in the nuclear fuel materials the BeO has been found to be most compatible for the UO2 fuel as an additive to enhance the thermal conductivity. BeO has one of the highest thermal conductivity ceramics and can withstand the radiation environment and does not react with UO2 up to 2200°C. This study focuses on studying the performance of UO2-BeO using FRAPTRAN (fuel rod analysis program transient). FRAPTRAN is a fuel performance code used to calculate the response of single fuel rods to operational transients and hypothetical accidents at burnup levels up to 62 gigawatt-days per metric ton of uranium (GWd/MTU) [2, 3]. This code is typically used for analyzing fuel rod response to transients and accidents like reactivity induced accident
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