Strategic fuel management via implementation of a combined reload-reshuffle scheme in small modular reactors

Abstract

This study aims to implement a coupled fuel reload-reshuffle scheme for a PWR-based SMR. Considering 540 EFPD as the cycle length, a heterogenous poison-free core based on the design of ACP-100 with 57 fuel assemblies (FAs) utilizing three different enrichments (3.0 wt.%, 4.0 wt.%, and 4.45 wt.%) was modeled in SERPENT. Initially, the core achieved a k_eff of 1.31492 and a radial PPF of 1.77, which decreased to 1.10914 and 1.19 respectively at the end of the first cycle. Reloading 12 fresh FAs and shuffling 32 irradiated FAs within the core at this point increased the k_eff to 1.1584, sustaining criticality for an additional 540 EFPDs (the second cycle). Two more burnup cycles were simulated with the refueling patterns being established by evaluating the assembly discharge burnup and core power profile. Through a hybrid combination of in-out and out-in loading approaches, a high cumulative average discharge burnup exceeding 30 MWD/kg (over 40 MWD/kg for some assemblies) was achieved at the end of the fourth cycle (2160 EFPDs). Although the employed refueling patterns raised the power peaking factors (PPFs) at the beginning of each cycle, the core power distribution in general became more uniform and the PPF decreased as burnup progressed. Other than the beginning of the fourth cycle, the obtained PPF values were less than or around 2.00 even without the use of any control systems. Both the fuel and moderator temperature coefficients remained sufficiently negative throughout the burnup cycles. Further iterations of the implemented refueling schemes can be carried out depending on plant operational requirements.