The effect of neutron irradiation on recovery (annealing) of irradiation damage has been investigated for self-ion implanted Si. A damage layer was introduced by 200 keV Si+ implantation to a fluence of 5 x 10(14) Si/cm(2) at room temperature. The damaged samples were neutron-irradiated to 3.8 x 10(19) n/cm(2) (fast neutron), without intentional heating, in the core of the Kyoto University Reactor. During neutron irradiation, the samples were heated only by nuclear reactions, and the irradiation temperature was estimated to be less than 90 degrees C The damage levels of the samples were characterized by Rutherford backscattering with channeling. Reduction of damage peaks as a result of neutron irradiation was clearly observed in the samples. The annealing efficiency was calculated to be 0.44 defects/displacement. (C) 2014 Elsevier B.V. All rights reserved.