Bulk hydrogen retention in neutron-irradiated graphite at elevated temperatures

Bulk hydrogen retention and the analysis of absorption kinetics have been studied on graphite samples irradiated with neutrons at various fluences. There are two kinds of hydrogen trapping sites: interstitial cluster loop edge sites (trap 1) and carbon dangling bonds at edge surfaces of a crystallite (trap 2). Neutron irradiation preferably creates trap 2 sites at lower fluences and trap 1 sites at higher fluences. The dissociation enthalpy becomes 2–3 times higher for neutron-irradiated samples due to the creation of high energy trapping sites. Absorption kinetics, such as diffusion coefficients and absorption rate constants are strongly affected by neutron irradiation and annealing after irradiation.