Se(-II) immobilization in Fe(II)-(hydro)oxides; Coprecipitation and post-transformation behavior

Francisco, P. C. M.  ; Ishidera, Takamitsu ; Tachi, Yukio  

As a key long-lived fission product in high-level wastes (HLW), Se-79 presents a significant contribution to the long-term radiological hazards associated with geological HLW disposal. Thus, its behavior is important for the performance assessment of geological HLW repositories. Under reducing conditions Se exists as Se(-II). A possible retardation pathway for Se(-II) species is via interaction with aqueous Fe(II) from the corrosion of the steel canister enclosing the waste matrix. There is relatively little information on Se(-II) uptake involving coprecipitation with poorly crystalline iron phases and subsequent behavior during phase transformation. Batch coprecipitation and crystallization experiments of Se(-II) with Fe(II) phases under N atmosphere and reducing conditions were carried out. Rapid Se(-II) uptake was observed during coprecipitation. During aging, Se(-II) was observed both as discrete phases and surface complexes.