Performance of an i -SANEX System Based on a Water-Soluble BTP under Continuous Irradiation in a γ-Radiolysis Test Loop

Abstract

The i-SANEX solvent formulation consisting of nominally 0.2 M TODGA/5% 1-octanol/dodecane was γ-irradiated under realistic conditions in the Idaho National Laboratory radiolysis test loop, in contact with both extraction and stripping aqueous phases. The extraction aqueous phase was 4.5 M HNO3, and the stripping aqueous phase was 0.018 M SO3–Ph–BTP/0.35 M HNO3. When irradiated in contact with only the 4.5 M HNO3 phase, the TODGA solvent maintained excellent extraction performance for americium, cerium, europium, and neodymium to a maximum absorbed dose of nearly 0.9 MGy. The results for preliminary static, batch irradiations were consistent with test loop findings. When the aqueous phase was changed to that containing the aqueous soluble BTP, the irradiated aqueous phase showed a dramatic color change, but this does not appear to have had adverse effect on solvent extraction performance. The distribution ratios for both the lanthanides and actinides were invariant with absorbed dose, and the separation factors were essentially unchanged to a maximum absorbed dose of 174 kGy. The results of inductively coupled plasma mass spectrometry analysis of the aqueous and organic phases showed that ruthenium and strontium were not extracted in the presence of the irradiated BTP-aqueous phase. Molybdenum was extracted under both conditions. Further, the buildup of corrosion products of stainless steel in the presence of the BTP was not dramatically greater than in the nitric acid-only system. Phase separation times were not adversely affected by irradiation for either system. The results presented here indicate that the performance of the TODGA/SO3–Ph–BTP, i-SANEX process under test loop radiolysis is much better than expected based on a literature report using single-phase batch irradiation experiments, and better than might be predicted based on diglycolamide radiolysis studies alone