TY - JOUR A1 - Ruiz-Hervias, J. A1 - Simbruner, Kai A1 - Cristobal-Beneyto, M. A1 - Perez-Gallego, D. A1 - Zencker, Uwe T1 - Failure mechanisms in unirradiated ZIRLO® cladding with radial hydrides N2 - The purpose of this paper is to investigate the relationship between hydride morphology, in particular the presence of radial hydrides (RHs), stress state and failure mechanisms associated with the ring compression test (RCT). Samples of ZIRLO®cladding were pre-hydrided and subjected to thermo-mechanical treatments to precipitate long radial hydrides. The results show that the reorientation treatment was very successful. A considerable fraction of RHs was generated, the radial hydride continuity factor being around 80 to 90% of the wall thickness. The samples with reoriented hydrides were tested using the RCT at room temperature. Macroscopic brittle failure was observed with sudden load drops for displacements around 0.5 mm, with a calculated “offset strain”between 0.5 and 1%. Crack nucleation occurs in RHs located in regions with the highest values of hoop stress. These locations are the inner diameter of cladding at the vertical plane of the sample (12 and 6 o’clock positions) and the outer diameter at the horizontal plane (3 and 9 o’clock positions). Noticeable load drops in the RCT are associated with unstable crack propagation events through the radial hydride network, the crack front reaching up to 90% of the wall thickness in some cases. The failure micro-mechanism is quasi-cleavage in the hydrides and micro-void nucleation, growth and coalescence in the Zr matrix, with ductile tearing patches connecting neighboring hydrides. The main conclusion is that radial hydride metrics is not the only parameter that determines cladding failure in the presence of RHs, but the interaction between the location and continuity of RHs and the stress normal to the hydride (the hoop stress in this case). Consequently, if a radial hydride is located at a position within the cladding where the hoop stress is small, a crack will not be initiated easily in the RCT. KW - ZIRLO® KW - Cladding Embrittlement KW - Radial Hydrides KW - Failure Mechanism KW - Ring compression test PY - 2021 DO - https://doi.org/10.1016/j.jnucmat.2020.152668 SN - 0022-3115 VL - 544 SP - 152668 PB - Elsevier B.V. AN - OPUS4-52000 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Simbruner, Kai A1 - Billone, Michael C. A1 - Zencker, Uwe A1 - Liu, Yung Y. A1 - Völzke, Holger T1 - Brittle failure analysis and modeling of high-burnup PWR fuel cladding alloys N2 - The aim of this research is the development of methods for predicting mechanical behavior and identification of limiting conditions to prevent brittle failure of high-burnup (HBU) pressure water reactor (PWR) fuel cladding alloys. A finite element (FE) model of the ring compression test (RCT) was created to analyze the failure behavior of zirconium-based alloys with radial hydrides during the RCT. An elastic-plastic material model describes the zirconium alloy. The stress-strain curve needed for the elastic-plastic material model was derived by inverse finite element analyses. Cohesive zone modeling is used to reproduce sudden load drops during RCT loading. Based on the failure mechanism in non-irradiated ZIRLO® claddings, a micro-mechanical model was developed that distinguishes between brittle failure along hydrides and ductile failure of the zirconium matrix. Two different cohesive laws representing these types of failure are present in the same cohesive interface. The key differences between these constitutive laws are the cohesive strength, the stress at which damage initiates, and the cohesive energy, which is the damage energy dissipated by the cohesive zone. Statistically generated matrix-hydride distributions were mapped onto the cohesive elements and simulations with focus on the first load drop were performed. Computational results are in good agreement with the RCT results conducted on high-burnup M5® samples. It could be shown that crack initiation and propagation strongly depend on the specific configuration of hydrides and matrix material in the fracture area. KW - Cladding KW - Radial hydrides KW - Ring compression test KW - Cohesive zone model PY - 2024 DO - https://doi.org/10.1515/kern-2024-0109 SN - 2195-8580 SP - 1 EP - 9 PB - Walter de Gruyter GmbH AN - OPUS4-62409 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -