The release of metal fission products from pyrocarbon-coated UO2 particles was studied by means of post-irradiation annealing at temperatures ranging from 1600 to 2300C. The release of 106Ru and 155Eu was controlled by diffusion in the kernel, at temperatures above 1800C. The reduced diffusion coefficients in the kernel were very similar, at temperatures ranging from 1900 to 2300C, and could be described by:

Ru:     D (m2/s) = 1.1 x 106 exp[-704(kJ/mol)/RT]

Eu:     D (m2/s) = 3.8 x 106 exp[-637(kJ/mol)/RT]

K.Hayashi, K.Fukuda: Journal of Nuclear Materials, 1990, 174, 35-44