Core region materials

In this chapter, after giving an overview of the embrittlement of Western pressurized water reactor (PWR) reactor pressure vessel (RPV) beltline materials, together with the characteristics of PWR RPVs, such as their general specification, core region materials and the effects of variables on embrittlement, the surveillance database obtained from US, French and Japanese nuclear power plants (NPPs) and those from other countries is presented based on open literature. The surveillance program of each country is also briefiy described. Trends of surveillance data which will be obtained in the near future are described. The possibility of new data from reconstituted and miniature specimen techniques is described. 

Cables with multiple-layer sheathing have plastic-insulated cores. Solid PE or sintered PE is used as the plastic. Sintered PE is a foamed polyethylene material that has different electrical properties than solid PE. Under certain circumstances the core region is filled with a petrolatum material to give protection against... 

Fig. la. Atomic structure ofa two-dimensional nano-structured material. For the sake of clarity, the atoms in the centers of the crystals are indicated in black. The ones in the boundary core regions are represented by open circles. Both types of atoms are assumed to be chemically identical b Atomic arrangement in a two-dimensional glass (hard sphere model), c Atomic structure of a two-dimensional nanostructured material consisting Of elastically distorted crystallites. The distortion results from the incorporation of large solute atoms. In the vicinity of the large solute atoms, the lattice planes are curved as indicated in the crystallite on the lower left side. This is not so if all atoms have the same size as indicated in Fig. la [13]... 

The pseudopotential method relies on the separation (in both energy and space) of electrons into core and valence electrons and implies that most physical and chemical properties of materials are determined by valence electrons in the interstitial region. One can therefore combine the full ionic potential with that of the core electrons to give an effective potential (called the pseudopotential), which acts on the valence electrons only. On top of this, one can also remove the rapid oscillations of the valence wavefunctions inside the core region such that the resulting wavefunction and potential are smooth. 

Regularity of microstructure is readily investigated, but it was of interest to see whether ferroelectric domains and boundaries could be revealed in lattice images. Evidence on this is given below. In addition, the materials afforded opportunity for observations of structural relaxation in the core regions of large dislocations. 

In oxides, the division between core and valence states should be carried out with care. For example, in strongly ionic materials the cation may have lost all valence electrons to the anion and so the cation/anion interaction involves orbitals on the cation that are atomic core states. In this situation, expHcit inclusion of the outermost cation orbitals would be required for accurate results. Even so, the replacement of the core region with a smoother potential can reduce the calculation time even for H atoms, and so pseudopotentials are available even in this case. 

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