Behavior and microstructure of ferritic steels irradiated in the Phenix reactor

This paper deals with the irradiation behavior of three ferritic steels, namely F17 (17Cr), EM12 (9Cr-2MoNbV) and EM10 (9Cr-1Mo). These alloys were irradiated up to 100 dpa in Phenix as samples or wrapper tubes. The immersion density measurements confirm their high swelling resistance, but the tensile and impact tests reveal great differences in their mechanical properties. The DBTT of F17 is strongly increased, and compared to an aging treatment the irradiation amplifies and shifts its embrittlement towards the low temperatures. In contrast to F17, the mechanical properties of EM10 are nearly not affected by irradiation, and EM12 has an intermediate behavior. The TEM examinations show that all the small density variations come from irradiation-induced voids and that the F17 embrittlement results from α 'phase formation enhanced by irradiation. In conclusion, EM10 is by far the most attractive candidate for wrapper applications. Its fully martensitic structure implies an improved swelling resistance and its chemical composition should inhibit the microstructural instabilities which are responsible of the embrittlement of F17 and EM12