Numerical investigation of interfacial stability and crack-induced cohesive degradation in Cr-coated zircaloy-4 cladding under LOCA conditions

The interfacial integrity of chromium (Cr)-coated Zircaloy-4 (Zry-4) cladding under Loss-of-Coolant Accident (LOCA) conditions is critical to maintaining its protective function. A coupled thermo-mechanical and cohesive-zone framework was developed within MOOSE to investigate substrate burst behavior and coating–substrate interfacial degradation. The baseline model was benchmarked against a selected uncoated Zry-4 Severe Accident Test Station (SATS) experiment, reproducing the burst time of approximately 437 s. Cohesive zone modeling (CZM) was subsequently introduced together with prescribed through-thickness transverse coating cracks. The continuous coating remained interfacially stable before substrate burst, whereas a baseline crack with a 1 μm initial opening width generated highly localized mixed-mode loading, with tangential and tensile-normal tractions of approximately 97 and 49 MPa, respectively, and a maximum cohesive damage of approximately 0.55 without complete separation. Parametric analyses showed that the crack-induced response was substantially more sensitive to interfacial strength than to the critical energy release rate, while varying the initial crack opening from 1 to 20 μm produced only minor changes in the local response. Increasing crack number did not proportionally increase the maximum damage, and the average damaged-interface length per crack decreased with increasing segmentation. Increasing the Cr coating thickness from 5 to 20 μm delayed the predicted substrate burst from 439.6 to 444.8 s but increased the maximum cohesive damage from approximately 0.41 to 0.84. These results identify coating cracks as local sources of interfacial degradation and reveal a trade-off between improved burst resistance and increased demand on interfacial integrity.