An innovative Method to study Volatile Fission Products speciation in nuclear fuels under Severe Accident Conditions

Abstract : The development of realistic models for fission products behavior during a severe accident requires experimental data on fission products speciation into the fuel (as irradiated and during the transient) together with thermodynamic predictions. Due to the limitations in terms of experiments and characterization techniques available to study fission products speciation in nuclear irradiated fuels, simulant materials (SIMFUEL manufactured thanks to conventional process) are often used. However, these materials do not allow the study of volatile fission products because they are totally released during the sintering stage. In the case of SIMFUEL with implanted fission products surrogates, the chemical state and the corresponding evolution of the phases during the thermal sequence are not entirely representative of the real case. An innovative method to study volatile fission products speciation in SIMFUEL samples has thus been developed. Spark plasma sintering was used to synthesize dense SIMFUEL samples containing cesium in collaboration with the JRC-Karlsruhe within the frame of the GENTLE program. Thermodynamic calculations made using the TAF-ID v.6 associated with the FACTSage software enabled to determine the conditions in which to perform thermal treatments. In-temperature XAS experiments in conditions representative of a sevre accident are developed in collaboration with FAME-UHD beamline at the ESRF (Grenoble, France). Additional thermal treatments will also be performed to enable further characterizations (ceramography, SEM-EDX...).