Neutronic and fuel cycle performance of LEU fuel with different means of excess reactivity control: Impact of neutron leakage and refueling scheme

Abstract

Low enriched uranium (LEU) fuel with different Integral Burnable Absorbers (IBAs) and Burnable Poison Rods (BPRs) in AP1000 assembly was investigated. These include IBAs of Gd2O3, Er2O3, AmO2, PaO2, and BPRs of Al2O3-B4C. The conventional uranium dioxide (UO2) fuel and two accident tolerant fuels (ATFs) namely UN-U3Si2 and U3Si2 were taken as the base fuel materials. Nine fuel compositions of these fuels with and without burnable poison were simulated in the lattice physics code Dragon, version 5. The burnup-dependent infinite multiplication factor was determined and significant variation was found due to the addition of poison. Reactivity was calculated at different levels of neutron leakage (0–5%). More positive reactivity at the early burnup stage and less negative reactivity at end of life were found for PaO2. The Linear Reactivity Model (LRM) was used to calculate the fuel cycle parameters. Cycle burnup and discharge burnup were determined considering different refueling batch number at each leakage scenario. Both parameters are found to decrease with neutron leakage while a large batch number results in a higher discharge burnup. Reduced discharge burnup was observed for each IBA and BPR except PaO2. Cycle length was also calculated for each of the composition and cycle length penalty was positive only for PaO2. The fuel temperature coefficient of reactivity, pin power distribution, and energy-dependent neutron flux were determined using the Monte Carlo code OpenMC. The burnup-dependent isotopic compositions were also studied.