Core aerosol formation

This report, though dated, provides a thorough discussion of the physical phenomena that affect fission product release and aerosol formation during the interactions of core debris with concrete. 

The behavior of metal ions in reversed micelles may be more interesting, since the reversed micelle provides less solvated metal ions in its core (Sunamoto and Hamada, 1978). Through kinetic studies on the hydrolysis of the p-nitrophenyl ester of norleucine in reversed micelles of Aerosol OT and CC14 which solubilize aqueous cupric nitrate, Sunamoto et al. (1978) observed the formation of naked copper(II) ion this easily formed a complex with the substrate ester (formation constant kc = 108—109). The complexed substrate was rapidly hydrolyzed by free water molecules acting as effective nucleophiles. 

The flow rate accepted by the interface ranges between 100 and lOOOnL/min for most applications. The interfacing mechanism is based on the formation of the aerosol in high-vacuum conditions, followed by a quick droplet desolvation and the hnal vaporization of the solute on a target surface prior to ionization. The process is fast and requires less than 8 mm of path length. At the core of the interface there are a nano-nebulizer and a treated surface. The nebulizer tip... 

Finally, in the discussion of reverse microemulsion systems, mention should be made of one of the most widely studied systems. The surfactant, sodium bis(2-ethylhexyl) sulfosuccinate or Aerosol-OT (AOT), is one of the most thoroughly studied reverse micelleforming surfactants since it readily forms reverse micelle and microemulsion phases in a multitude of different solvents without the addition of cosurfactants or other solvent modifiers. The phase behavior of AOT in liquid alkane/water systems is already well documented. Indeed, the first report of the existence of the formation of microemulsions in a supercritical fluid involved an AOT/alkane/ water system. A The spherical structure of an AOT/nonpolar-fluid/ water microemulsion droplet is shown in Fig. 1. In the now well-known structure, it can be seen that the two hydrocarbon tails of each AOT molecule point outward into the nonpolar phase (e g., supercritical fluid). These tails are lipophilic and are solvated by the nonpolar continuous phase solvent whereas the hydrophilic head groups are always positioned in the aqueous core. 

Such interactions can only occur, however, when the volatile fission products and the primary aerosols appear simultaneously in the primary system, in spite of the large differences in their volatilization behavior. As was discussed above, uniform thermal-hydraulic conditions do not prevail within the reactor core during a severe accident (for example, the peripheral fuel rods may fail relatively late in the accident sequence, at a point when a large part of the central rods may already be molten) and it can be assumed that the broad time-envelope of significant release of structural aerosols will encompass the release of the volatile fission products. However, as was mentioned in Section 7.3.1.2., the amount of primary aerosols formed and the timing of their formation depend highly on the specific accident sequence this is particularly true for the control rod materials. 

In general, it can be assumed that the reaction between silver and iodine species in the gas phase, as well as the reaction of iodine vapor with silver aerosol or with silver deposited on the primary circuit surfaces, is only of minor significance for iodine behavior in the course of a severe accident. The main reasons are the rather short residence time of the silver aerosols in the gas phase, the fact that iodine and silver volatilization from the reactor core may differ considerably over time and, finally, the small proportion of elemental I2 and of HI (compared with the Csl fraction) assumed to be present in the gas phase during transport through the primary circuit. In contrast, Agl formation is expected to proceed to a significant extent later on in the containment sump water (see Section 7.3.3.3.3.). 

Not only does the fraction of the fission product core inventory reaching the containment depend on the particular accident sequence, the same is true for the chemical forms of the fission products, which result in part from reactions within the primary system, as has been discussed in Section 7.3.2. However, when fission products are transported from the high-temperature reducing conditions of the primary system to the lower-temperature, predominantly oxidizing and condensing steam conditions of the containment, their chemical forms may change again simultaneously, fission products deposited on the surfaces of bulk material aerosols could be resuspended due to the formation of more volatile species. 

As has been discussed in the preceding sections, the containment of a nuclear power plant represents a very effective passive barrier, at least for a certain period of time, for confining the radionuclides released from the reactor core and from the primary system in a severe accident. This renders possible their plate-out from the containment atmosphere by natural processes such as deposition of aerosols or, as regards iodine, formation of non-volatile compounds, as well as by the action of engineered safety features (e. g. sprays). Nevertheless, in safety considerations it has to be assumed that the containment is not a permanent and absolutly tight confinement, but that there would be several fundamental mechanisms by which a certain fraction of the radionuclides could escape from the containment. The most important of these mechanisms are... 

In the synthesis of these macromolecular system, many parameters involved can affect the information associated with the binding sites, such as functional monomers/polymers, crosslinkers and solvents/porogens. Thus, both the feasibility of imprinting and the proper preparation conditions need exploration for the preparation of efficient imprinted materials (Liu Z. et al., 2010). It is important to state that MIP can be obtained in different formats, depending on the preparation method followed. To date, the most common polymerizations for preparing MIPs involve conventional solution, suspension, precipitation, multi-step swelling and emulsion core-shell. There are also other methods, such as aerosol or surface rearrangement of latex particles, but they are not used routinely (Puoci et al., 2011). 

A recent study reported the formation of bamboo nanostructures with different morphologies from turpentine oil by the aerosol route at 1000 °C. FcH was used as a catalyst source and sulfur as a promoter [40]. These structures have sharp tips, bamboo shapes, open ends, hemispherical caps, pipe-like morphology, and metal particles trapped inside the wide hollow cores. 

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