Comparative study of fission product release of homogeneous and heterogeneous high-burn up MOX fuel by Knudsen Effusion Mass Spectrometry supported by EPMA, SEM/TEM and thermal diffusivity investigations

The fission product release of two irradiated mixed oxide (MOX) fuel variants from the high burn-up disk irradiation test IFA-655 in the Halden reactor was investigated by Knudsen Effusion Mass Spectrometry (KEMS). The fresh samples were provided and characterised within the NFIR11NFIR: https://www.epri.com/portfolio/programs/108031 program. Both fresh fuel variants contained 16 wt.% plutonium but differed principally by the distribution of the plutonium: in one it was heterogeneously dispersed, in the other one homogeneously. The fission products release (Kr, Xe, I, Cs, Te, Sr, Nd) measured by KEMS as a function of annealing temperature is reported. The gas release (including helium) has been measured quantitatively. The interpretation of the release measurements is supported by microstructure and elemental analyses (SEM, TEM, EPMA). A correlation has been made with results from thermal diffusivity measurements obtained on the same fuels.