Point defects are of course very important in a nuclear complex as they are created either by irradiation or by accommodation of impurities (e. g., fission prod­ucts (FP)) (see Chapter 1.02, Fundamental Point Defect Properties in Ceramics and Chapter 1.03, Radiation-Induced Effects on Microstructure). More generally, they have a tremendous role in the kinetic properties of the materials. It is therefore not surprising if countless ab initio studies exist on point defects in nuclear materials. Most of them are based on a supercell approach in which the unit cell of the perfect crystal is periodically repeated up to the larg­est possible simulation box. A point defect is then introduced, and the structure is allowed to relax. By difference with the defect-free structure, one can cal­culate the formation energy ofthe defect that drives its equilibrium concentration. Some care must be taken in writing this difference as the number and types of atoms should be preserved in the process. Point defects are also the perfect object for the saddle point calcula­tions that give the energy that drives their kinetic properties. Ab initio permits accurate calculation of these energies and also consideration of (for insulating materials) the various possible charge states of the defects. They have shown that the properties of defects can vary greatly with their charge states.

Many different kinds of defects can be considered. A list of possible defects follows with the characteristic associated thermodynamical and kinetic energies.