Our aim is to study the neutronic behaviour of potential accident-tolerant fuel (ATF) claddings in a pressurised water reactor under normal operations. This work compares ATF silicon carbide composite (SiC/SiC) cladding to conventional ZIRLO^TM cladding in APR-1400. Additionally, a “sandwich” cladding design developed by the CEA is used for SiC/SiC. The design structure includes a liner in between two layers of the composite to ensure leak tightness. The two proposed liners are Niobium (Nb) and Tantalum (Ta). Serpent 2, a Monte Carlo reactor physics lattice code, is employed to model both cladding materials in APR-1400 at three different levels: pin cell, fuel assembly, and core. The criticality, neutron spectrum, actinide inventory, and power distribution as a function of burnup are investigated. The simulations show that SiC/SiC with the Nb liner displays a far superior performance than the Ta liner across all examined characteristics. Ta leads to a harder neutron spectrum and increased Pu-239 content throughout the cycle, while Nb presents negligible effects. In fact, SiC/SiC with the Nb liner performs very similarly to ZIRLO^TM at all model levels. The results indicate that, in terms of neutronics, the adoption of the SiC/SiC composite would entail little to no changes to current APR-1400 operations.

A numerical framework leveraging finite element analysis is established to examine the thermomechanical behavior and burst safety of a novel accident‐tolerant fuel (ATF) cladding design. This design incorporates a thin niobium (Nb) liner positioned between two layers of silicon carbide ceramic matrix composites (SiC‐CMC). The burst safety is assessed through a probabilistic failure analysis utilizing Weibull theory, accounting for the scatter in the apparent strength of SiC‐CMC and the associated size effect. By examining variations in Nb layer thickness and pellet‐clad gap thickness, the primary focus is on assessing the burst safety of the sandwich claddings in an APR1400 fuel system under both steady operation and loss‐of‐coolant accident (LOCA) scenarios. The findings indicate sandwich claddings are likely to function without fracture or leakage for both the original thickness (82.5 µm) and reduced gap thicknesses of up to 70 µm. However, a further reduction to 57.5 µm in gap thickness is likely to lead to cladding failure during steady operation. This research leverages computational modeling to gain a foundational insight into the thermomechanical performance of SiC‐CMC/Nb sandwich claddings in nuclear fuel rods and provides predictive tools aimed at augmenting the safety and reliability of next‐generation nuclear power plants.