Oxidation behavior of Cr-coated zirconium alloy cladding in high-temperature steam above 1200 °C

Abstract

Dense, uniform, and well-adhered chromium (Cr) coatings were deposited on zirconium (Zr) alloy claddings by using physical vapor deposition (PVD). The Cr-coated samples were tested at 1200 oC and 1300 oC, respectively, for different exposure time in water steam environment. Microstructures and compositions of the coating/substrate system after oxidation were characterized by X-ray diffraction, scanning electronic microscopy, and energy dispersion spectrometer. The microstructural results clearly demonstrated that Cr2O3 layer has been produced on the coating surface, acting as an oxygen diffusion barrier and concomitantly reducing the oxidation rate. The experimental results on weight gains soundly supported the microstructural findings that the Cr coatings could protect the Zr substrate from high-temperature steam oxidation, even at a temperature up to 1300 oC. Finally, the oxidation kinetics was theoretically analyzed and the underlying oxidation mechanism was also clarified.

Recent Advances in Protective Coatings for Accident Tolerant Zr-Based Fuel Claddings

“…10 times longer than current LOCA criteria). Ma et al showed that Cr coatings could protect Zr-1Nb alloy from HT steam oxidation at 1200 and 1300 • C (Figure 5) [95]. It was shown that the thickness of the formed Cr 2 O 3 and residual Cr layers depends on oxidation time, which is probably due to the combined effect of the ongoing redox reactions between chromium oxide and zirconium, also observed by Han et al [96].…”

“…Optical and SEM images of Cr-coated zirconium alloy cladding after high-temperature steam oxidation at 1200 °C for 0.5 h (a), 1 h (b), 2 h (c), 4 h (d), and 1300 °C for 0.5 h (e) and 1 h (f). Reproduced from[95].…”

Corrosion Behavior of Chromium Coated Zy-4 Cladding under CANDU Primary Circuit Conditions

“…However, at elevated temperatures and pressures, this passive oxide layer continues to grow up to a critical thickness, beyond which the protective tetragonal phase transforms into a rapidly growing non-protective monoclinic oxide phase [16][17][18]. The unstable oxide growth causes internal stresses and crack formation, eventually resulting in coating breakdown and corrosion The main advantages of coated cladding [19] include:…”

“…The appearance of water side corrosion of the fuel cladding and hydrogen uptake in the cladding at high burnup are the main limitations to burnup extension of nuclear fuel [19].…”

“…Cr-based coatings perform well under such conditions due to the successful growth of a protective Cr 2 O 3 . The major demerit observed initially was that Cr 2 O 3 scale can only withstand the service temperature up to ~1200 • C when exposed to steam [19].…”