This paper deals with the irradiation behavior of three ferritic steels, namely F17 (17Cr), EM12 (9Cr-2MoNbV) and EM10 (9Cr-lMo). These alloys were irradiated up to 100 dpa in Phénix as samples or wrapper tubes. The immersion density measurements confirm their high swelling resistance, but the tensile and impact tests reveal great differences in mechanical properties. The ductile-brittle transition temperature (DBTT) of F17 is strongly increased, and compared to an aging treatment, the irradiation amplifies and shifts the embrittlement towards lower temperatures. In contrast to F17, the mechanical properties of EM10 are unaffected by irradiation, while EM12 has an intermediate behavior.

The transmission electron microscopy (TEM) examinations show that all the small density changes come from irradiation-induced voids and that the embrittlement of F17 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 provides an improved swelling resistance and its chemical composition should inhibit the microstructural instabilities that are responsible for the embrittlement of F17 and EM12.