Neutronic examination of the U–Mo accident tolerant fuel for VVER-1200 reactors

In this study, we investigated the possibility of employing accident tolerant fuel (ATF) in VVER-1200/V491 assembly without gadolinium-containing fuel rods using the Monte Carlo code Serpent 1.1.7 with ENDF/B-VII cross-section library. The analysis involves assembly design with reflective boundary conditions. To compare the neutronic performances, U–5Mo, U-7.5Mo, U–10Mo, and U–15Mo fuels were chosen in addition to ordinary UO2 fuel. The concentration of 135Xe, 149Sm, fissile and fertile isotopes with burnup, reactivity feedback with fuel temperature variation, and βeff values were calculated. The results indicate that the fuel cycle length increases by 54.27% for U–5Mo, 32.6% for U-7.5Mo, and 13.8% for U–10Mo, while it decreases by 16.4% for U–15Mo fuel. Additionally, the effect of 95Mo content in natural Mo was investigated by reducing the 95Mo concentration. According to the results, each proposed fuel's fuel cycle length extended when the depletion ratio of 95Mo increased. Additionally, the calculations for reactivity feedback guarantee safe operating conditions for all U-xMo fuels.