Title: Zr alloy protection against high-temperature oxidation: double-layered coating with active and passive functional properties

Biography:

Irena Kratochvilova obtained very important results which were published in prestigious journals and were cited by scientific community. She has published 85 papers in impacted journals.  She has been working in the Institute of Physics AS CR and teaching at the Faculty of Nuclear Engineering Czech Technical University.

Abstract

In this work we investigated the hot steam oxidation of ZIRLO fuel cladding coated with a double layer consisting of 500 nm nanocrystalline diamond (NCD) as the bottom layer and 2 mm chromium-aluminum-silicon nitride (CrAlSiN) as the upper layer. Coated and noncoated ZIRLO samples were exposed for 4 days at 400 °C in an autoclave (working water-cooled nuclear reactor temperature) and for 60 minutes at 1000 °C (nuclear reactor accident temperature) in a hot steam furnace. We have shown that the NCD coating protects the Zr alloy surface against oxidation in an active way: carbon from NCD layer enters the Zr alloy surface and, by changing the physical and chemical properties of the Zr cladding tube surface, limits the Zr oxidation process. In contrast, the passive CrAlSiN coating prevents the Zr cladding tube surface from coming into physical contact with the hot steam. The advantages of the double layer were demonstrated, particularly in terms of hot (accident-temperature) oxidation kinetics: in the initial stage, CrAlSiN acts as an impermeable barrier, but after a longer time, the protection by CrAlSiN decreases as an increasing number of cracks in the carbon of NCD penetrate the Zr cladding surface and worsen conditions for Zr oxidation. For the double-layer coating, the underlying NCD layer mitigates thermal expansion, reducing cracks and defects in upper layer CrAlSiN.