Distributions of volatile fission products in or near the fuel-cladding gap of the FBR MOX fuel pins irradiated to high burn-up

Microstructural and chemical characterization of medium burnup fast reactor MOX using electron microscopy

“…The question remains whether the accumulation of the fission products, particularly Cs, has caused the recrystallization process. HBS formation has already been observed on the outermost part of the SFR pellets [23]. SFR fuel does not show the typical increase in local fission density on the periphery originating the HBS formation; instead, the recrysatllization is confined to this area by the irradiation temperatures [22].…”

Interpretation and modelling of fission product Ba and Mo releases from fuel

“…In fuel, molybdenum can exist either in solid solution within the UO 2AEx matrix, in metallic precipitates (the noble metal ''white" phase) and, occasionally, in the grey phase [28][29][30][31] (at the fuelcladding gap of certain fuels for example). The solubility of molybdenum in urania was calculated to be very limited using atomic scale calculations [32].…”

“…The solubility of molybdenum in urania was calculated to be very limited using atomic scale calculations [32]. Cesium molybdate (Cs 2 MoO 4 ) is suspected to participate in molybdenum redistribution within the fuel and in molybdenum release from fuel [33,29,31,34]. Since a very low content of Mo is observed in the grey phase, the impact of BaMoO 4ðgÞ on molybdenum release is neglected hereafter.…”

Investigation of the Cs2(Mo,Te)O4 Solid Solution and Implications on the Joint Oxyde-Gaine System in Fast Neutron Reactors

“…Various irradiation tests and post-irradiation examinations of MOX fuels in FNR prototypes have shown a specific behavior not previously observed in the light-water reactor fuels. In particular, the formation of an oxide fission products layer (up to a few hundred micrometers in thickness) between the fuel and the cladding, named “Joint Oxyde-Gaine” or JOG (the French term for the oxide-cladding joint), has been observed. − This layer is formed by volatile and semi-volatile fission product elements, mainly cesium, molybdenum, iodine, tellurium, and palladium, that migrate from the center of the fuel pellet ( T ≃ 2300 K) toward the edge, due to the strong radial thermal gradient (≃450 K mm –1 ), and accumulate between the fuel and the cladding, where the temperature is lower ( T ≃ 973 K). Knowing the thermal and mechanical properties of this layer is crucial for the safety assessment of the reactor.…”