Some practical methodologies to assess the overall high temperature (one-sided) steam oxidation protectiveness of chromium-based coatings on a zirconium-based substrate, as Enhanced – Accident tolerant (Nuclear) fuels (E-ATF) claddings
Jean-Christophe Brachet, Thomas Guilbert, Stéphane Urvoy, Elodie Rouesne, Marion Peyret, Thierry Vandenberghe, Cédric Prou, Thai Le Hong, D. Hamon
Abstract
• Critical overview and suggestion of efficient experimental methodologies to assess the overall Cr-based coatings protectiveness on a Zr-based substrate upon High-Temperature one-sided oxidation, • Use of Weight Gain coupling with oxide scale thickness to deduce the averaged overall oxygen quantity having diffused into the metallic substrate. Use of post-quenching micro-hardness measurements less costly to correctly estimate through-wall clad oxygen diffusion profiles, • Necessity of taking into account the additional prior-β Zr hardening due to Cr diffusion into the Zr-based substrate upon HT transients, which depends on the oxidation temperature and final cooling scenario. Among various Enhanced-Accident Tolerant nuclear fuel claddings studied worldwide, Cr-coated Zr-based claddings are largely considered as a reference with evolutionary design and resulting ability to improve the high-temperature (HT) oxidation resistance. Most of the numerous studies carried out so far on the HT oxidation behavior of coated claddings have focused on detailed localized post-mortem examinations. The present paper aims to suggest complementary and sufficiently simple experimental methodologies to evaluate the overall protectiveness of Cr-based coated materials upon HT steam oxidation. The different proposed approaches have been assessed by comparing their capacity to characterize the Cr-coating loss of protectiveness and the associated oxygen diffusion into the sub-coating metallic wall-clad thickness. The latter is then compared to the results obtained by “more direct” Electron-Probe-Micro-Analysis measurements. The overall oxygen ingress into the tested coated claddings, evaluated by different proposed approaches, can be correlated to the Post-Quenching strength of the claddings, using a novel “Equivalent Cladding Reacted” parameter - called “Equivalent Chromium Reacted” ECrR – recently developed at CEA.