b'Figure 3. Change in keff of the reactor with different fuels (the reference UCO fuel and eight UN fuel options). It is seen that the keff of the UN-pellet-fueled HP-MR options decreases more slowly throughout the cycle length and their initial excess reactivity is significantly lower, due to their increased U/U-235 contents. Note that a similar amount of U-235 is consumed during the same time interval regardless of the fuel optionThis neutronics screening of high-density ceramics fuels in a thermal-spectrum microreactor examines the trade-offs between total mass of uranium, U-235 enrichment, and N-15 enrichment, and can be used as the basis for a detailed cost/benefit analysis.U-235 enrichment (~20% less onU-235 mass in the UN solid pellet average) than the baseline UCOfuels, despite their ~3 times lower fuel. Because the fuel/compactU-235 enrichment. As the reactor volume ratio of the TRISO fuelpower remained constant, a similar options was smaller than 5%, theamount of U-235 was consumed fuel material volume in the UNduring the same time interval solid fuel pellets was ~20 timesregardless of the fuel option. There-higher, which resulted in the ~20fore, a smaller percentage of U-235 times lower discharge burnup. Thiswas consumed in the UN-pellet-also resulted in the ~6 times higherfueled HP-MR than the TRISO-fueled 126 2023|AFC ACCOMPLISHMENTS'