The retention of H in graphites and carbon-fiber/carbon composites was studied with regard to crystallographic data which had been obtained by using X-ray diffraction techniques. It was noted that the amounts of retained H varied, between samples, by a factor of up to 16. After irradiation to 1.9 x 1024/m2 (0.2dpa), the retained H contents became 20 to 50 times greater those in non-irradiated samples. A strong correlation was observed between the degree of H retention and the lattice constant. The crystallite size was also closely related to H retention. It was suggested that H atoms were trapped at dangling C bonds at the edge surfaces of crystallites, which were thermally stable even at temperatures above 1000C. Differences in the amount of H gas which was desorbed from graphite-type materials could also be explained in terms of this model.

H.Atsumi, M.Iseki, T.Shikama: Journal of Nuclear Materials, 1996, 233-237B, 1128-32