Carbon-14 is an important radionuclide in the inventory of radioactive waste. In Switzerland, the 14C inventory in a cement-based repository for low- and intermediate-level radioactive waste (L/ILW) is mainly associated with activated steel (?85 %). In light water reactors (LWR) 14C is the product of 14N activation in steel parts exposed to thermal neutron flux. 14C has been identified a key radionuclide in safety assessments. Release of 14C occurs due to slow corrosion of activated steel in the near field of a deep geological repository. While the 14C inventory is well known, the speciation of 14C upon release from activated steel is only poorly understood. The present study is aimed at investigating the formation of carbon species during the anoxic corrosion of iron and steel and determining the 14C species formed in a corrosion experiment with activated steel. The experiments were carried out in conditions similar to those anticipated in the near field of a cement-based repository.