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 diffusivity of Cs in the pyrocarbon layer could be described by:

D (m2/s) = 0.0012 exp[-412(kJ/mol)/RT]

at temperatures ranging from 1600 to 2300C.

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