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.
Highlights
The Fukushima-Daiichi nuclear accident in Japan caused by earthquake and tsunami in 2011 has drawn worldwide attention to power plant safety under accident conditions
Oxidation experiments Weight gain of the Zr tubes with or without Cr coating was comparatively measured during the whole oxidation process, and the weight gain per surface area is plotted as a function of an oxidation duration time, as shown in Supplementary Fig. 1
Since the Cr coating was produced only on the outside surface (NOT two surfaces) of the Zr cladding, one can see that the weight gain of the outer surface of Cr-coated Zr is extremely low in comparison with that of the uncoated one
Summary
The Fukushima-Daiichi nuclear accident in Japan caused by earthquake and tsunami in 2011 has drawn worldwide attention to power plant safety under accident conditions. The Zr alloys will be oxidized rapidly with steam to produce a large quantity of exothermal energy and hydrogen at the loss of coolant accident (LOCA) scenario. After this nuclear accident, accident tolerant fuel (ATF) development programs were started in many countries[1,2,3,4]. Compared with the current UO2 (pallet)-Zr (cladding) system, ATF is a new fuel pallet-cladding that could improve the safety of the fuel assemblies beyond the design basis accident (DBA). The major potential approaches for the development of ATF are improving pallet or cladding properties. Several candidate fuels and claddings have been designed and investigated[5]
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