Fission product behaviour in phenix fuel pins at high burnup

Abstract In FBR fuel pins, the evolution of the fuel fission product chemistry with increasing burnup leads to strong modifications in the fission product and fuel behaviour. The present work is focused on unstrained and uncorroded Phenix pins, irradiated in steady state conditions up to 14% ha burnup. A transition period is clearly exhibited between 7 and 9% ha burnup with the following consistent events: opening of the fuel-to-clad joint filled with fission product compounds, decrease of the pellet area, increase of the fission gas release, fission gas bubble precipitation inside the fuel matrix, decrease of the intragranular cesium content, drop of molybdenum content in the “noble metal” precipitates. The electron microprobe analyses allow to point out a coherent behaviour between the fission product movements out of the fuel pellet and the fuel-to-clad joint filling. They also indicate that both dissolved xenon and intragranular cesium have a similar behaviour at peak power node.