Abstract
The isotope 94Nb (t1/2 = 2.04 ∙ 104 a) is produced during the operation of nuclear reactors due to the neutron activation of 93Nb present in reactor vessels. Related waste streams will be disposed of in cement-based repositories for low and intermediate level wastes (L/ILW).The retention of niobium by cement was investigated using a combination of 95Nb and natural 93Nb. Sorption experiments assessed also the impact of iso-saccharinic acid (ISA) and chloride on Nb retention, both expected in specific L/ILW.Sorption experiments revealed a strong uptake of Nb by cement. Isotopic exchange with 93Nb in HCP partly explains 95Nb uptake, although sorption on C-S-H is tentatively proposed as main retention process. Sorption of Nb is weakly affected by chloride, but decreases importantly at [ISA] ≥ 10−3 M reflecting the formation of (Ca-)Nb(V)-ISA complexes. This work provides key inputs to assess 94Nb retention in the Safety Case context of nuclear waste repositories.
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