Fission product precipitates in irradiated uranium carbonitride fuel

Austenitic steel-cladded uranium carbonitride fuel pins were irradiated in the BR2 up to 6.4% burnup. A cross-section of the pin RV 24 with the fuel composition UC0.86N0.09O0.05 was prepared for X-ray microanalysis of the fission product precipitates. Rare-earth oxide and U(Mo,Tc)C2 phases were observed in the whole fuel region. Bright phases present in annular rings of the outer fuel zone were identified as U2(Tc, Ru, Rh)C2. Alkaline-earth oxide and U–Pd–Ni phases were shown in the fuel-cladding gap. The rare-earth and alkaline-earth fission products extracted the oxygen from the fuel matrix which became nearly oxygen free. The formation of nitrides could not be detected.