Helium precipitation study in UO2 by Transmission Electron Microscopy

International audienc

Helium precipitation study in UO2_2 by Transmission Electron Microscopy

International audienc

Fission products at the fuel-cladding interface of PWR fuel rods: morphological and chemical study

During irradiation in light water reactors, numerous fission products are produced by the fission reactions. At the periphery of the fuel, these elements implant by recoil in the cladding inner oxide layer (zirconia) located at the fuel-cladding interface. In the present study, two irradiated UO2 fuel rods with different burnups (37.3 and 61.4 GWd/tU) have been analyzed. The coupling of FIB-SEM tomography and S/TEM-EDS chemical analyses allowed 3D analysis of the distribution, sizes, shape and chemical composition of the bubbles and precipitates of fission products in zirconia. The fission product structure, observed in the two samples was quite similar. A complex morphology of the fission product agglomerates have been highlighted. They are organized in three parts: the bubble (Xe), the deposit (Cs, I) and the metallic precipitates (Mo, Tc, Ru, Rh, Pd, Sn). Tellurium is partly found with the deposit, but also with the metallic precipitates. Different kind of bubbles have been observed, classified by size, potentially linked to different steps of growth. In particular, Xe form bubbles arranged in three populations: sub and/or nanobubbles within the grains and along the grain boundaries (< 1 nm), larger bubbles (a few nanometers to a few tens of nanometers) anchored to the metallic precipitates, and finally, much larger bubbles (several tens to several hundreds of nanometers), which are part of more complex systems, and are also stuck to metallic precipitates

Experimental determination of cesium and iodine speciation in UO2 as a function of temperature and oxygen partial pressure

International audienc

Experimental determination of cesium and iodine speciation in UO2 as a function of temperature and oxygen partial pressure

International audienc

Experimental determination of cesium and iodine speciation in UO2 as a function of temperature and oxygen partial pressure

International audienc

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°C or 1h at 1200°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.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.RST/Reactor Physics and Nuclear MaterialsDea

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

International audienceThe interactions of iodine and caesium in UO2 have been investigated. For this purpose, implanted UO2 samples were thermally treated (4h at 900°C or 1h at 1200°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