Role de l'iodure de cesium sur le developpement des reactions combustible-gaine

TEM of thin foils taken from irradiated fuel element ((UPu)O_2?x fuel in type 316 stainless steel cladding) shows precipitates rich in iron and chromium in the fuel, together with a reduction of chromium content in the cladding. We have undertaken simulation experiments out-of-pile to study the compatibility, both isothermally and in thermal gradients, of the steel/CsI and steel/(CsI + UO ₂) systems, making use of metallography, X-ray diffraction and microprobe analysis, with a view to gaining a better understanding of the reactions at the fuel cladding interface in reactor service. The results of the simulation and reactor-irradiation experiments have enabled us to prepare a transport mechanism in the gas phase, of van Arkel type, involving stainsless steel (at low temperature), (UPu)O_2±x (at high temperature) caesium iodide serving as vector. This transport mechanism which essentially involves displacement of manganese, chromium and iron from cold zones to hot zones, is possible only in the presence of an oxygen source (and the mixed oxide, (UPu)O_2±x, in particular).