We use molecular dynamics simulations to study the irradiation-induced point-defect clustering kinetics in CeO2 as a surrogate for UO2, the most widely used nuclear fuel. Remarkably, the cluster-formation mechanism involves a partial self-healing response of the perfect crystal to the radiation-induced defects, by spontaneous creation of new point defects with negative formation energy. These "structural" defects neutralize the cluster by screening its long-range Coulomb potential, thereby localizing the damage. The observation of a similar lattice response in MgO and UO2, in spite of very different types of clusters involved, suggests that this partial self-healing screening behavior may be intrinsic to all ionic crystals.