Behaviour of fission products in UO2: Experimental characterization of the Cs-I-UO2 model system at high temperature

The interactions of iodine and caesium in UO2 have been investigated. For this purpose, implanted UO2 samples were thermally treated (4h at 900 degrees C or 1h at 1200 degrees C) under controlled atmosphere (0.03% H2O/H2) and then characterized by several experimental techniques for their structural and chemical studies. Thermodynamic calculations were also performed in order to optimize heat treatment conditions before performing tests, and to help in the interpretation of results afterwards. The sample characterizations after thermal treatments reveal the presence of bubbles and precipitates (mean diameter around 10 -20 nm) and have allowed to clearly identify the presence of CsI in these bubbles which is in agreement with the calculations. The chemical form of the observed precipitates is not well defined yet, due to the lack of experimental reference spectra, but they consist very likely of caesium uranates, as predicted by the thermodynamic calculations.

Automated summary

The study investigated the interactions of iodine and caesium in UO2. Implantation of UO2 samples followed by thermal treatment (4h at 900 degrees C or 1h at 1200 degrees C) under controlled atmosphere (0.03% H2O/H2) allowed for characterization of their structure and chemistry through various experimental techniques. Thermodynamic calculations were used to optimize the heat treatment conditions and interpret the results. The analysis of the treated samples revealed the presence of bubbles and precipitates, with CsI identified within the bubbles in agreement with the calculations. The chemical composition of the observed precipitates, likely caesium uranates, remains unclear due to the lack of experimental reference spectra.