The international VERDON-ISTP program aims to research and mitigate the risk of radioactive product emissions into the environment in the event of a severe nuclear accident. Among these, some experiments include heating fuel pellets to very high temperatures to monitor the release of fission products. Experimental data on the microstructure and chemical composition of nuclear fuel in the final environment (oxidizing or reducing) can be integrated into scenario codes to better predict its behavior in the event of an accident.
Providing a safe environment for handling and analyzing radioactive samples, while also providing information on the composition from sub-micrometer areas with excellent accuracy, shielded EPMA is the tool of choice to describe the distribution and chemical composition of fission products in different phases.
In this specific series of experiments, the shielded EPMA method allows for the observation of interactions occurring between nuclear fuel and cladding materials. As shown above, under oxidizing conditions, diffusion between U and Zr occurs at the interface between the fuel and the cladding. Quantitative charts generated in this area show a diffusion distance of approximately 70 µm.
Shielded EPMA is also used to accurately analyze the molten region (U, Pu, Zr)O 2 penetrating into the cracks of the pellet in a reducing environment, and to study the impact of the environment on the composition of fission products ('white impurities' including Mo, Ru, Rh, Pd, and metallic Tc).
Data from CEA Cadarache, France (CEA / DES / IRESNE / DEC / SA3E)
Le Gall et al., Journal of Nuclear Materials 530 (2020) 151948
Le Gall et al., Journal of Nuclear Materials 531 (2020) 152015