Carbon-14 Speciation During Anoxic Corrosion of Activated Steel in a Repository Environment

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