Advanced Coatings of Nuclear Fuel Cladding

A new anticorrosion strategy for Zr nuclear fuel claddings will be presented and explained. The dissertation deals with a protection of zirconium (Zr) nuclear fuel cladding material against corrosion in water-cooled nuclear reactors by coating by polycrystalline diamond (PCD) or chromium-aluminum-silicon nitrate (CrAlSiN) layers. It was shown that Zr alloy surfaces can be effectively protected against oxygen and hydrogen uptake at both accident and working temperatures in water-cooled nuclear reactor environments by coating the Zr surface by PCD layer or CrAlSiN each in specific way and for specific purpose. PCD layer consists of two different carbon phases: diamond and sp2 hybridized carbon. Protective PCD layer is thin 300 – 700 nm and its best application is to reduce Zr nuclear fuel cladding tubes corrosion at operating temperature (typically by 40 %) and thus prolong the lifetime of nuclear cladding and consequently enhance nuclear fuel burn-up. In addition to the fact that PCD layers prevent the surface of Zr alloys from direct interaction with hot water/steam, carbon released from the PCD film enters and changes the physical properties of the underlying Zr surface. On the contrary, CrAlSiN coatings is 2 – 4,5 μm thick one phase layer. CrAlSiN coating serves as a full barrier against oxygen diffusion mainly at high temperature steam around 1000 °C, strongly depending on absence of mechanical defects. Next step will be combinations of both specific anticorrosion strategies of Zr alloy cladding tubes coating: changing of conditions for corrosion process (PCD coating) and preventing physical contact of Zr cladding tubes surface with hot steam/water specially at accident temperatures (CrAlSiN coating).

Školitel: doc. Ing. Irena Kratochvílová, Ph.D.