The inhomogeneity of cometary nuclei emerges in the fact that there are some active areas on the surface of a cometary nucleus which are sources of observed gas-and-dust jets. The active regions of a cometary nucleus are formed by local disruption of the dust layer, though a possible mechanism of this disruption are not clear. We investigated the temperature distribution on the icy bottom and dust walls of the crater on the surface of a cometary nucleus and the effect of amplification of sublimation due to the concentration of the solar radiation by the conical hole depending on its geometrical parameters and on the nucleus rotation.