BISON Analysis of Silicon Carbide Cladding Separate Effects Mechanical Tests that Mimic Reactivity Initiated Accidents

With the need for commercial reactors to address the world’s need for a safe low carbon emitting energy source, light water reactor (LWR) cladding material capabilities have been studied. Many advanced cladding materials have addressed critical needs in high mechanical strength, radiation tolerance and low thermal conductivity as part of the accident tolerant fuel (ATF) campaign. In this study, a candidate for ATF cladding material, silicon carbide-fiber/silicon carbide-matrix (SiC-f/SiC-m), a SiC composite, was investigated. BISON, a nuclear fuel performance code, simulated SiC-f/SiC-m in reactivity-initiated accident (RIA) transients and separate effects mechanical modified burst tests (MBT) data [1] were used for comparison to the BISON simulation results. The analyses performed in these studies modeled relative RIA pulse widths (100, 50 and 10 milliseconds (ms)) that are analogous to various pressurization rates (1.75, 3.6 and 18 GPa/s). The BISON simulations predicted SiC-f/SiC-m cladding tubes to burst at ~0.2% hoop strain. A parametric study was performed to exercise the capabilities of the BISON elasticity models. A Sobol sensitivity study was also performed to not only verify the results of the parametric study that demonstrated the ultimate tensile strength (UTS) was the most influential parameter that determines the burst hoop strain, but also quantified the impact the UTS makes on the four burst conditions: burst time, burst pressure, burst hoop strain, and burst strain rate. In addition to concluding SiC-f/SiC-m bursts at low hoop strains in comparison to traditional Zirconium (Zr)-based cladding, the authors discuss the importance in understanding the prediction of failure and how these failure mechanisms can influence failure criteria for SiC-f/SiC-m reactor safety guidelines.