Interlayers for Cr-coated nuclear fuel claddings
Résumé
Grown with an adequate process, an external Cr coating undeniably improves the robustness of zirconium-based nuclear fuel claddings, especially upon hypothetical high temperature accident conditions such as Loss-of-Coolant-Accident (LOCA) [1, 2]. However, beyond design-based-accident conditions encountered above 1200°C, the Cr-Zr binary system is subject to interdiffusion [3]. In addition to decreasing the Cr quantity available for the protection against high-temperature oxidation by forming an outer Cr2O3 layer, interdiffusion induces Cr-Zr eutectic reaction above 1300°C [3]. One solution to mitigate this effect and increase even more the resistance of Cr-coated claddings in LOCA (and beyond) conditions, is the deposition of an interlayer between the Cr coating and the Zr-based substrate, acting as a diffusion barrier.
This paper covers briefly the identification and selection criteria of a relevant interlayer material in connection with its deposition process. A case study is detailed with the deposition of a Mo interlayer by magnetron sputtering, topped by a Cr layer (around 12 µm) on zirconium flat coupons. The beneficial effect of the Mo interlayer thickness (2 and 4 µm) on the performances of the coated Zr-based substrates is discussed regarding high-temperature oxidation tests in dry and wet air. Additionally, microstructural investigations are carried out after and before the tests to get more insights into the bilayer Cr-Mo coated Zr substrate evolution at high temperature.
Domaines
Matériaux
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