Compositional changes have been measured at grain boundaries, dislocation loops, and precipitates in Japanese ferritic/martensitic steel (JFMS, fusion candidate ferritic/ martensitic steel) and high purity Fe-10Cr, Fe-10Cr-1Ni and Fe-10Cr-5Ni model alloys irradiated with 1 or 1.25 MeV electrons in a high voltage electron microscope (HVEM). The depletion of chromium at grain boundaries and nearby matrices is derived in all alloys above 300°C. The enrichment of silicon as well as the depletion of chromium is observed at grain boundaries and precipitate (MC, M6C and M23C6)-matrix interfaces in JFMS. These decompositions obey the conventional solute size dependence. On the other hand, the segregation of nickel seems to depend on the bias of the sinks. The void swelling and the precipitate stability in ferritic steels are discussed based on the present information on defect-solute interactions, loop bias, and solute-precipitate interactions.