Chemically and microstructurally modulated high-temperature release of CsI in Nd-doped UO2 nanoceramics

The unexpected discharge of instant release fraction elements, such as Cs and I, from irradiated nuclear fuel, is one of the most concerning severe events that may occur during in-pile irradiation, the subsequent storage and final disposal, yet the underlying chemistry behind their release is poorly understood. Herein, we have examined the speciation of CsI within UO 2 nanoceramics doped with Nd as a proxy for high burn-up fuel, which was synthesised via spark plasma sintering. We demonstrate via X-ray absorption spectroscopy and electron microscopy that the addition of Nd has an impact upon the chemical speciation and dissociation of CsI in the examined materials. High temperature release studies using Knudsen effusion mass spectrometry reveal varying release patterns corresponding to Nd addition. The results of this investigation indicate that the chemistry of the UO 2 high burn-up fuel matrix, its specific microstructure and associated soluble fission products impact the chemical speciation and the high temperature release of Cs and I within irradiated fuel.