[en] The properties of Fe additions in Zr-2.5Nb pressure tube alloy are investigated after plastic deformations, heat treatments below its monotectoid temperature and severe radiation damage by neutrons and ions. Mössbauer spectra showed that in the β-quenched and hot-extruded Zr-2.5Nb about 80% of Fe atoms is located in βZr and the reminder in a metastable ω-phase formed within βZr filaments retained in αZr grain boundaries. The fraction of Fe in ω-phase increased to ∼40% after heat treatment at 400 °C for 24 h in vacuum, and also after intense cold rolling, service in the reactor core and ion implantation. In samples with β-phase fully transformed at ∼560–580 °C to βNb, Fe in ω-phase didn't appear after any cold work, while in untransformed samples the fraction of Fe in ω-phase clearly increased with the extent of cold-rolling. A large s-electron density observed at ⁵⁷Fe nuclei in ω-phase suggests that iron atoms in this phase are mostly located in low-volume B-sites, with hybridized sd² trigonal, partially covalent orbitals.