Full-core fuel analysis of a soluble boron-free SMR: Pellet-cladding interaction issue and enhancing fuel safety through loading pattern design

The full-core fuel behavior of the Soluble Boron-Free (SBF) Small Modular Reactor (SMR) was analyzed and compared with conventional pressurized water reactors (PWRs) and Soluble Boron-Using (SBU) SMRs to evaluate unique pellet-cladding interaction (PCI) risks. Unlike PWRs and SBU SMRs, SBF SMRs rely on control rods for reactivity control, leading to localized power increases during late-cycle withdrawal. This significantly elevates cladding hoop stress, particularly in fuel rods near control rods, increasing PCI risks even at moderate burnups. The maximum local cladding hoop stress due to PCI in SBF SMRs exceeds that of conventional PWRs, posing new fuel safety and qualification challenges despite being SMR fuel characteristics, such as lower power density, and extended relative fuel plenum length. Comparisons with boiling water reactors (BWRs) highlight the heightened PCI risk in SBF SMRs due to differences in core design and control strategies. A fuel loading strategy that positions high-burnup rods away from lead control rod banks effectively reduces peak cladding stress. However, PCI remains a concern, particularly for long-cycle cores with LEU+ fuel. These findings emphasize the need to integrate fuel performance considerations early in SBF SMR development to ensure safety, regulatory compliance, and adaptability for future LEU+ fuels.