Fast neutron bombardment of graphite displaces carbon atoms to interstitial positions and produces lattice vacancies. Upon heating the interstitial disturbances become mobile, move to more stable positions and release stored energy. The thermal release of stored energy was investigated by relative specific heat measurements, which are described in detail. Data are presented which show the dependence of energy storage upon extent of neutron bombardment and upon temperature of bombardment. Activation energy spectra for the thermal release of stored energy are calculated. The general trends of the data are discussed. Estimates are made of the numbers of interstitial carbon atoms, interstitial carbon (C2) molecules, and lattice vacancies in a sample of low bombardment. It is suggested that annealing of irradiated graphite causes much of the interstitial material to reintegrate with the graphite lattice by filling lattice vacancies.