This article presents a novel method combining ion irradiation, in-situ transmission electron microscopy (TEM), and microchemistry analysis before/after irradiation, which allows to examine same microstructural areas throughout ion irradiation. A 12 wt% Cr Ferritic/Martensitic steel (HT9) was irradiated in the TEM to 1.17 x 10(20) ions.m(-2) at 440 degrees C...