Lessons learnt from VERCORS tests.: Study of the active role played by UO2–ZrO2–FP interactions on irradiated fuel collapse temperature

The VERCORS experimental program was launched in order to study radionuclide release from standard PWR fuels and quantify the corresponding source term in severe-accident conditions. Performed by the CEA, it forms part of a larger program concerning reactor-accident studies funded by the IRSN in collaboration with EDF. Twenty-five experiments have been performed leading to a large database regarding release of fission products and actinides from UO2 and MOX fuels under several types of atmosphere. The fuel burn-up ranges from 38 GWd/t to 70 GWd/t. Nearly all the tests were performed in such a way as to measure with some accuracy the fuel temperature. The present paper gives an overview of the program (i.e. sample and loop description, general FPs behaviour), with emphasis on the potential effect of UO2–ZrO2–FP interactions on fuel collapse temperature.