Abstract
Hydrogen uptake by nuclear fuel claddings during normal operation as well as loss of coolant during design basis and severe accidents beyond design basis has a high safety relevance because hydrogen degrade the mechanical properties of the zirconium alloys applied as cladding material. Currently, claddings with enhanced accident tolerance are under development. One group of such accident tolerant fuel (ATF) claddings are zirconium alloys with surface coatings reducing corrosion and high-temperature oxidation rate, as well as the chemical heat and hydrogen release during hypothetical accidents. The hydrogen permeation through the coating is an important parameter ensuring material safety. In this work, the hydrogen permeation of Ti2AlC and Cr2AlC MAX phase coatings on Zircaloy-4 is investigated by means of neutron radiography. Both coatings are robust hydrogen diffusion barriers that effectively suppress hydrogen permeation into the matrix.
Highlights
Worldwide many efforts are made after the Fukushima accident in 2011 to develop nuclear fuel components with enhanced accident tolerance
In the framework of characterization of the material compounds, various methods were applied including for instance X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and oxidation experiments in steam at temperatures up to 1500 °C
The crystallinity of both MAX phase materials is slightly different. While both coatings show significant differences in crystallite size probably stemming from their different annealing temperatures, the Ti2AlC coatings show XRD signals of various lattice planes and the Cr2AlC coatings show mainly signals of basal-plane
Summary
Worldwide many efforts are made after the Fukushima accident in 2011 to develop nuclear fuel components with enhanced accident tolerance. Besides the improvement of fuel properties like thermal conductivity, claddings with improved oxidation performance at temperatures of 1200 °C and above are under development. Such materials should enlarge the time until failure significantly by decreasing the release of hydrogen and chemical heat from the reaction with hot steam and/or by increasing the failure temperature, for instance the melting point [2]. Metallic claddings made for instance of FeCrAl alloys, showing significant lower oxidation rate with high-temperature steam along with a much lower chemical heat and hydrogen release;. Zirconium alloys coated with materials owning lower reaction rate like chromium or MAX phases. First neutron radiography investigations of the hydrogen permeability through Ti2AlC and Cr2AlC MAX phase coatings on Zry-4 are described in this paper
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