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At the equilibrium state, there is a balance between concentrations of various point defects. The number of defects may be described by the equations similar to the law of mass action. In this work, we use such approach and molecular dynamics simulations to calculate equilibrium concentrations of defects for different nuclear fuels: UN, UO2, and UC. We show that some types of phase transitions may be described as the accumulation of point defects. Namely, we consider (1) superionic transition and melting at heating and (2) appearance of pure uranium in uranium-rich composition. We discuss the reasons of narrow homogeneity area for UN, which is observed in the phase diagram. Also, we pay attention to the grounds of strong heat capacity increase occurring for all mentioned fuels at heating.