Radioiodine abatement – Development of radioiodine targeting strategies in the light of zero emission

Abstract

The abatement of iodine plays an important role in ensuring nuclear energy has minimal environmental impacts. During nuclear fuel recycling I-129 is typically released into the off-gas where current methods of abatement revolve around capturing the iodine and discharging it in a less harmful aqueous stream. This work looks at the potential of changing current radioiodine abatement practices by developing methods to augment current practice to selectively remove iodine from the aqueous phase with the long term view of immobilisation of iodine in a suitable wasteform for long term disposal. 12 metalated-silica based iodine targeting sorbents were screened for implementation in this abatement technology, including the use of Cu, Bi and Ag. The best performing materials under simulated caustic conditions were Ag based materials with aminothiourea (72 mg g−1) and mercapto-ligands (64 mg g−1). Under simulated conditions representing the liquid effluent arising from off-gas caustic scrubber, both copper and silver containing absorbents decreased (average ∼80% and ∼15% respectively) relative to equilibrium. Work progressed towards dynamic column experiments, where a 50% reduction in uptake relative to equilibrium experiments indicated hindered kinetics. Radiolytic stability experiments showed better iodide retention in the Ag-aminothiourea silica adsorbent (IX11), which did not release any iodide after irradiation. These materials were designed with methods of disposal in mind therefore ongoing work is investigating the cementitious encapsulation of these materials.