[en] Investigated was the effect of a neutron irradiation in the CM-2 type reactor at 150 deg C in the range of doses from 1.5x10¹⁹ to 5.1x10²¹ neutron/cm² (E > 0.1 MeV) upon the mechanical properties and the structure of vanadium and of the V-Zr-C alloy. It was shown that a strong irradiation strengthening is accompanied by a plastic instability which in vanadium appears at an exposure dose 10 times smaller than that causing a similar effect in the alloy. The correlation is examined between the plastic instability and the size, the density and the type of radiation defects. A comparison of the calculated and the experimental values of the radiation strengthening has been made. The suggestion is substantiated that carbon atom accumulations on annealing of irradiated specimens are produced by the decomposition of ''impurity-defect'' type complexes