Fission products and nuclear fuel behaviour under severe accident conditionsSpeciation of fission productsin the Verdon 3 and -4 samples
Résumé
During the irradiation of nuclear fuel in a light water reactor (LWR), fission products (FP) are created and retained in the fuel, modifying its microstructure and properties (thermal conductivity, creep behavior, etc.). In the case of failure of all the three containment barriers, as it could the case during a severe accident, FPs could be released from the fuel to the environment. The chemical nature of FP released from the fuel strongly depends on the scenario and the accident conditions involved (temperature, type of fuel, burn-up, oxygen potential, etc.). Moreover, chemical nature greatly affects FP behavior during their transport in the reactor and hence the source term. FP speciation in the fuel was studied in order to provide experimental data needed to support the speciation mechanisms currently proposed in the literature. Within the framework of the International Source Term Program, the VERDON-3 and-4 tests were devoted to high burn-up MOX fuel behavior and FP releases respectively under oxidizing and reducing conditions at very high temperature (up to 2570 K and 2800 K respectively). Qualitative and quantitative analyses on these fuel samples made it possible to obtain valuable information on fission product behavior in the fuel during the test as a function of the atmosphere. This presentation will provide a series of detailed characterizations including scanning electron microscopy (SEM) and optical microscopic (OM) observations, as well as electron probe microanalyses (EPMA) and Secondary Ion Mass Spectrometry (SIMS) of the VERDON-3 and -4 fuel samples before and after the test.
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