Thermodynamic study of actinides and lanthanides during total vaporisation of a very high burn-up UO2 fuel

A commercial PWR fuel sample of local burn-up of about 200 GWd/t was annealed in a Knudsen Cell Mass Spectrometer system (KCMS) with a temperature rate of 10 K/min up to 2750 K at which temperature the sample was completely vaporised. At high temperature the vapour above the sample contains mainly actinide and lanthanide oxides, the vapour pressure of refractory metals remaining below the detection limit. The local isotopic composition was determined by mass spectrometry and indicated a high content in higher actinides. From comparison of the partial vapour pressure with data for the pure oxides, obtained from experiments or literature, it is demonstrated that the actinide and lanthanide oxides dissolved in UO₂ matrix obey Henry’s law.