Severe core melt process

An important property of the primary condensation aerosols which is of high importance for the behavior of the volatile fission products is their large surface area. The surface area of the aerosols within the primary system of a severely damaged PWR can be approximately 500 times greater than that of the primary system structural surfaces (Beard et al., 1988 b). An aerosol mass of 1000 kg formed in a core melting process and having a specific surface area of 1 m /g has a total surface area of about 10 m. If one assinnes that the space needed for one fission... 

The details of the core melt-down processes depend both on the particular composition of the respective reactor core and on the particular conditions of the accident sequence under consideration. However, as a comparative evaluation of the results from different experiments on core melt progression performed in test reactors and from examination of the damaged core of the TMI-2 reactor (Hob-bins et al., 1991) has shown, in spite of considerable differences in the conditions and physical scales, several important phenomena seem to be common to all such events. Eutectic interactions between core materials cause the formation of liquid phases and loss of original core geometry at comparatively low temperatures (about 1500 K). The first liquids to be formed are metallic in nature and consist... 

The basic steps of the IM process produce unique structures in all molded products, whether they are miniature (micro) electronic components, compact discs, or large automotive bumpers. These structures have frequently been compared to plywood with several distinct layers, each with a different set of properties. In all IM products, a macroscopic skin-core structure results from the flow of melt into an empty cavity. Identifiable zones or regions within the skin are directly... 

Earth, has been prominent in models of the mantle for several decades (see Section 3.1.2). Such models are based upon a chondritic starting composition for the Earth, modified during core formation and perhaps in a magma ocean, and presuppose that there was a point in time when the mantle was totally homogenized. Whether the remnants of this primitive mantle can be identified today in modern basalts, or even in the early history of the Earth in Archaean basalts, is the subject of some debate. In favor are mantle melts with chondritic Os-isotope ratios (Fig. 3.32) and against are calculations which show that it is possible that the entire mantle has been processed through the subduction system (Section 3.1.6.4) during the history of the Earth. 

Fracture of massive brittle and ductile pieces are rather well understood. By taking proper account of the microstructure as well as the micro- and macro-defects, most catastrophic and fatigue failures find a satisfactory explanation within the scope of the linear elastic fracture mechanics or the elasto-plastic fracture mechanics. Metallic filaments are particular and in many respects deserve a treatment of their own. Particular fabrication methods, such as drawing, melt spinning or crystallization from the vapor phase for whiskers are needed to obtain their small lateral dimensions. These processes may give rise to particular textures, intrinsic and extrinsic defects. Thermal treatments may modify or eliminate such defects but in many cases fracture is initiated by defects that stem from the fabrication process. Moreover, the small lateral dimensions, especially in micro-wires, make metallic filaments prone to external influences. Corrosive attacks may rapidly affect an important fraction of their cross-section. Hydrogen, for instance, which usually results in a severe embrittlement, may diffuse up to the core in a rather short time. 

CdSe-CdS-ZnS core-multishell polymer nanocomposites were prepared by direct dispersion of CdSe-CdS-ZnS core-multishell QDs in an epoxy polymer matrix via a melt mixing technique. Nanocomposites filled with yellow-emitting QDs were more transparent than pure epoxy polymer. A shift in the luminescence of pure epoxy from the blue region to the yellow region was observed in the nanocomposite. Synthesized nanocomposites also showed enhanced tensile properties in comparison to pure epoxy polymer [236]. Several other studied reported the use of a melt blending process for the synthesis of semiconductor-polymer nanocomposites [237-241]. 

In the processes of fuel assembly destruction and melting and fuel performance in severe accidents, features of the KLT-20 such as a relatively low operating temperature of fuel, small quantities of materials and low core power density as compared to typical large capacity power reactors, are important. 

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