Enhanced Thermal Conductivity UO2-BeO Nuclear Fuel: Neutronic Performance Studies and Economic Analyses

The objective of this work was to continue the evaluation of the high thermal conductivity UO2-BeO (UBO) nuclear fuel. Current ceramic UO2 fuel offers many fuel performance benefits, but it has a low thermal conductivity. This results in high operating fuel temperatures, but this is a well-excepted performance compromise. Addition of Beryllium oxide to the fuel structure has been shown to increase the fuel thermal conductivity and provide positive neutronic benefits. Pellet heat conduction studies were performed at different linear heat generation rates (LHGR). At an average LHGR of 163.4 W/cm, UBO 10vol% fuel showed a decrease of 74 and 166 degrees C in the effective and centerline temperature, respectively. Similarly at a peak LHGR of 590 W/cm, UBO 10vol% fuel showed a decrease of 219 and 493 degrees C, respectively. A drawback to UBO fuel is the lower eutectic melting point. At 590 W/cm and beginning of cycle, the melting margin for UO2 and UBO 10vol% is 411 and 254 degrees C, respectively. Comparisons of fuel types were performed using 2D infinite lattice and 3D equilibrium core neutronic simulations. A 2D lattice analysis showed that an increased UBO fuel enrichment is necessary to maintain an equivalent cycle length as UO2 fuel. Using a mass equivalent 235U basis and the linear reactivity model for an 18-month cycle, UBO 5vol% and 10vol% fuel showed a cycle increase of 1.9 and 3.3 days, respectively. Similarly, the 3D core simulation showed a cycle increase of 2.2 and 3.3 days, respectively. However, the maximum 3D burnup was increased by 3707 and 7624 MWd/t, respectively, which may cause selective UBO placement. An economic analysis of UBO fuel compared the increased cycle length to the extra fuel costs associated with UBO fuel. The 18-month break-even fuel cost occurred at 4.03 and 8.15 days for the UBO 5vol% and 10vol% fuel, respectively. Since the computed cycle length was shorter than the break-even fuel cost, this resulted in a -12,365 and -25,712 $/reload-assembly penalty, respectively