The criterion of formation of a modulated structure by means of the spinodal mechanism in a spatial distribution of interacting vacancies (as strong concentrators of mechanical stresses) in metals as a target after irradiation is analyzed. For the irradiated body-centered cubic vanadium and tungsten, temperature dependences of the spatial periods of such a structure of the substitutional-vacancies’ subsystem are predicted taking into account the total mixing energies consisting of the energies of the (electro)chemical and strain-induced interactions between vacancies, which are cohesive by the nature in short distances and elastic by character at long distances, respectively.