The behaviour of fission products during fuel life in a nuclear reactor is of particular importance as it plays a significant role in the release kinetics during hypothetical reactor severe accident transients.
A description of (Cs, Mo, Ba) chemical states after some UO2 fuel irradiation stages is drawn. Molybdenum is supposed to be localised in a MoO2 precipitate (volatile over 1273K) and chemical reactions with condensed (Cs, Ba) oxides and/or uranates are possible.
According to this description, a coherent interpretation is presented for some accidental sequence tests providing new ideas for release mechanisms of (Cs, Mo, Ba) and an attempt is done to calculate their release with MFPR code, which is being developed by IBRAE in collaboration with IRSN.
(1) : IRSN
(2) : IBRAE