Uranium hexafluoride is used for the enrichment of 235U versus 238U. UF6 is obtained by fluorination of UF4 and its high volatility near room temperature makes it compatible with the gaseous centrifugation used for enrichment. The drawback of UF6 is his high reactivity with many materials such as metals. It is a strong fluorinating and oxidative agent which can lead to corrosion issues. From the synthesis to the isotopic separation, the uranium hexafluoride can be solid, liquid or gaseous. The study is focus on the interaction of iron with liquid and gaseous UF6. A first approach consisted in thermodynamics study of the U-Fe-F-O system. This led to identify the various stable phases in the experimental conditions. Fluorination of iron samples were then performed at 80°C under 3 bar of liquid UF6. In the early stage, UF6 reacted with iron and formed FeF2 and UFx (4&lt;x&lt;5). The nucleation took place in some particular sites which could be linked to crystal orientation. This will be investigated by EBSD. Then the growth and coalescence of those nodules, led to the formation of a continuous FeF2 layer and uranium fluoride or oxy-fluoride. Fluorination mechanism was investigated by intending to identify the diffusing elements and by determining the chemical reactions taking place. In order to understand these mechanisms some specific experiments (with gold deposit, gaseous UF6…) were performed and a corrosion mechanism has been proposed.

Corrosion mechanism of iron in liquid uranium hexafluoride environment

253rd National Meeting (2017)

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