Fission neutron irradiated nickel and electrically hydrogen-charged one as well as well-annealed nickel were investigated using positron annihilation lifetime spectroscopy (PALS). Long-lived positron lifetimes in the neutron irradiated nickel were observed, since vacancy clusters were formed due to the neutron irradiation. The introduction of hydrogen in pure well-annealed nickel by electrical charging resulted in the emergence of long-lived lifetime and its increase due to formation of defects. However, the long-lived positron lifetimes in the neutron irradiated nickel were shortened by electrical hydrogen-charging. The isochronal annealing behavior of the hydrogen-charged neutron irradiated nickel was also studied.