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Influence of high hydrogen content, on microstructure and mechanical behaviour, of zirconium alloys fuel cladding upon and after cooling from high temperature
Date : lundi 19 septembre 2016 à 14h00
Address : NeuroSpin Centre d'études de Saclay, 91191 Gif-sur-Yvette - amphithéatre J. Talairach
Abstract : Under hypothetical loss-of-coolant accident conditions, fuel cladding tubes made of zirconium alloys can be exposed to steam at high temperature (up 1 200°C) before being cooled and then quenched in water. In some conditions, after burst occurrence the cladding can rapidly absorb a significant amount of hydrogen (secondary hydriding), up to 3 000wt.ppm locally, during steam exposition at HT. The study deals with the effect, poorly studied up to date, of high contents of hydrogen on the metallurgical and mechanical properties of two zirconium alloys, Zircaloy-4 and M5®, during and after cooling from high temperatures, at which zirconium is in its ? phase. A specific facility was developed to homogeneously charge in hydrogen up to ~3 000wt.mass. cladding tube samples of several centimeters in length. Phase transformations, chemical element partitioning and hydrogen precipitation during cooling from the ? temperature domain of zirconium were studied by using several techniques, for the materials containing up to ~3 000wt.ppm of hydrogen in average: in-situ neutron diffraction upon cooling from 700°C, X-ray diffraction, μ-ERDA, EPMA and electron microscopy in particular.
The results were compared to thermodynamic predictions. In order to study the effect of high hydrogen contents on the mechanical behavior of the (prior-)? phase of zirconium, axial tensile tests were performed à various temperatures between 20 and 700°C upon cooling from the ? temperature domain, on samples with mean hydrogen contents up to ~3 000ppm-mass. The results show that metallurgical and mechanical properties of the (prior-)? phase of zirconium alloys strongly depend on temperature and hydrogen content.