Complexation of Cu2+, Ni2+ and UO22+ by radiolytic degradation products of bitumen

The influence of the radiolytic degradation products of bitumen on the speciation of radionuclides was studied under conditions which reflect those in the near field of a cementitious rad waste repository. The potential complexation capacity of the degradation products was studied and complexation experiments with Cu2+, Ni2+ and UO22+ were performed. In general 1:1 complexes with log K values of between 5.7 and 6.0 for Cu2+, 4.2 for Ni2+ and 6.1 for UO22+ were produced at an ionic strength of μ = 0.1. The values are in good agreement with those found in the literature for oxalate complexes and suggest that oxalate determines the speciation of Cu2+, Ni2+ and UO22+ in the bitumen water at pH ≤ 7. However, under the high pH conditions typical of the near field of a cementitious repository, competition with OH-ligands will be large and oxalate, therefore, will not play a significant role in the speciation of radionuclides. The main conclusion of the study is that the degradation products of bitumen will have no influence on radionuclide speciation in a cementitious near-field and, as such, should not be considered in appropriate safety assessment models. (orig.)