Carbon-14 speciation during anoxic corrosion of activated steel in a repository environment

Radioactive waste contains significant amounts of 14C which has been identified a key radionuclide in safety assessments. In Switzerland, the 14C inventory of a cement-based repository for low- and intermediate-level radioactive waste (L/ILW) is mainly associated with activated steel (~85 %). 14C is produced by 14N activation in steel parts exposed to thermal neutron flux in light water reactors. Release of 14C occurs in the near field of a deep geological repository due to anoxic corrosion of activated steel. Although the 14C inventory of the L/ILW repository and the sources of 14C are well known, the formation of 14C species during steel corrosion is only poorly understood. The aim of the present study was to identify and quantify the 14C-bearing carbon species formed during the anoxic corrosion of iron and steel and further to determine the 14C speciation in a corrosion experiment with activated steel. All experiments were conducted in conditions similar to those anticipated in the near field of a cement-based repository.