Ref.: MmeMnu11-002
Apresentador: Beatriz Soto Rovelo
Autores (Instituição): Rovelo, B.S.(Instituto de Pesquisas Energéticas e Nucleares); Francisco, L.H.(Instituto de Pesquisas Energéticas e Nucleares); Carvalho, G.G.(Instituto de Pesquisas Energéticas e Nucleares); Bustillos, J.O.(Instituto de Pesquisas Energéticas e Nucleares);
Resumo:
Over the past few years, clean energy demand has been increasing significantly worldwide. For Brazil in particular, the impact of the recent water crisis coupled with ongoing international conflicts resulted in a shortage of resources in the energy sector, in which nuclear energy would play an essential role in generating electricity in the near future. Most of the nuclear technology in Brazil is currently focused on the development and operation of pressurized water reactors (PWRs), which include critical components manufactured with zirconium alloys (Zircaloy-4), such as nuclear fuel cladding components. One of the main issues with these materials is their high permeability to hydrogen gas formed in the primary water circuit of PWRs, which may lead to phase transitions, defect formation, and eventually fracture of Zircaloy-4 components under extreme conditions that may occur during operation, posing major safety issues of nuclear fuel leakage. Hence, in this work, we investigated the dynamics of ZrH2 formation in Zircaloy-4 under extreme conditions that may occur in PWRs. Firstly, Zircaloy-4 hydridation was carried out in distilled water, where the metal alloy was submitted to a pressure of 150 atm under 380 °C in a sealed high-pressure asher vessel for 6 h, which did not result in hydride formation according to X-ray diffraction experiments. Additionally, Zircaloy-4 hydridation was also carried out in a tubular furnace utilizing an H2 gas pressure of 150 kPa under 700 °C for 75 and 150 min, where surface ZrO2 formation and a complete phase transition of the metal alloy to ZrH2 was observed with increasing exposure time, respectively. Furthermore, hydrogen content was also probed by elemental analysis, where a significant increase of over 160-fold was observed for non-hydrided (48.5 ppm of H) and hydrided Zircaloy-4 (8053 ppm of H). Scanning electron microscopy images also showed the impact of hydrogen adsorption resulting in visible cracks of over 50 µm in size in hydrided materials, in which the mechanical properties suffer severely from the formation of defects as a result of the alpha-Zr to ZrH2 phase transition.