Speaker
Description
Nuclear decontamination processes generate a wide range of radioactive waste to be properly managed. Spent ion-exchange resins (IER) are a large component of radioactive low and intermediate level waste. The development of suitable treatment and conditioning processes is an urgent task to address, as the challenging waste nature (flammability, dispersivity, swelling), high radionuclides leachability (e.g.: Cs) and final waste package volumes do not comply with Waste Acceptance Criteria (WAC) of modern nuclear waste repositories.
Nowadays, advanced pre-treatment processes are preferred to direct encapsulation of spent IER, to reduce organics content and volume of the package, thus limiting corrosion and flammability troubles, and optimizing footprint and costs of the final repository. In this work, IER thermal incineration and Fenton-like wet oxidation have been studied at laboratory scale. A stepwise thermal treatment based on spent IER incineration is being optimized by slowing the gasification process to gradually convert cesium volatile species into inorganic and thermally stable compounds. A simplified surrogate waste was prepared by loading nuclear grade cationic IER with CsNO3 solutions. Thermogravimetric analysis has allowed to optimize residence time and temperature ramp rate, to enhance the conversion of the (-SO3-Cs+) functional group into less-volatile cesium sulphate. Incineration has been performed into a muffle furnace up to 800 °C. The obtained ashes have been characterized by Raman and X-Ray Diffraction (XRD) analyses, while Cs retention efficiency has been calculated by Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) analysis. The wet oxidation process has been optimized by tuning temperature, catalyst and oxidant concentration. The decomposition over time of a surrogate waste containing Cs, Co, Sr and Ni, as representatives of activation and fission products contamination, has been monitored by Raman and FT-IR spectroscopy. The residue left after treatment has been investigated by XRD to prove the process efficacy. The nuclides distribution has been monitored by ICP-MS analysis. Finally, the obtained ashes and sludges will undergo encapsulation into a geopolymer matrix as promising alternative to Ordinary Portland Cement, to provide physical and chemical stability according to the WAC.
Dry and wet oxidation tests showed a promising weight reduction and good organic decomposition of the treated spent IER. For resin batches treated at 800 °C, promisingly high cesium retention into the ashes has been obtained. A homogeneous residue and a weight reduction rate of 40% turned out from optimization of wet oxidation. Ongoing activities are focused on developing and characterizing residue geopolymer encapsulation for long-term disposal.
| Speaker's title | Mr |
|---|---|
| Affiliation | Politecnico di Milano |
| Do you wish to participate as a Young Professional? | Yes |
| Do you wish to be considered for a Young Professional grant? | Yes |
