Hydrogen solubility measurements and the analysis of absorption kinetics have been studied on graphite irradiated with neutrons at various fluences up to 5.4×1024 n/m2. The absorption of hydrogen could be expressed as a diffusion-controlled process. The rate constant of hydrogen absorption was different from that for desorption. This difference may be ascribed to the effects of trapping sites in graphite. After neutron irradiation at 1.9×1024 n/m2 (~ 0.2 dpa), the hydrogen solubility was 20–50 times larger than that of unirradiated samples. The increase of hydrogen solubility was saturated above the damage level of ~ 0.3 dpa. The diffusivity of hydrogen was decreased by neutron irradiation up to 1.9×1024 n/m2, and then increased above this fluence. This behavior can be ascribed to the production of the trapping sites for hydrogen, and the elongation of the distance between the basal planes by neutron irradiation.
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