Cobalt transport

Isolated polynucleotide clusters from Rhodococcus opacus which encode four polypeptides possessing the activities of a NHase (a and /3 subunits), an auxiliary protein P15K that activates the NHase, and a cobalt transporter protein were expressed in Escherichia coli DSM 14459 cells [34]. Methionine nitrile was added continuously to a suspension of the transformant cells (5.6% w/v of wet cells) in phosphate buffer (50 mM, pH 7.5) at 20 °C, at a rate where the nitrile concentration did not exceed 15 g L 1 while maintaining the pH constant at 7.5. After 320 min, the nitrile was completely converted into amide, corresponding to a final product concentration of 176 gL1.4-Methylthio-a-hydroxybutyramide is readily hydrolyzed with calcium hydroxide, where the calcium salt of 4-methylthio-a-hydroxybutyric acid (MHA) can be directly used as a nutritional supplement in animal feed as an alternative to methionine or MHA. 

As with PWRs, a detailed knowledge of the relative significance of each of the possible sources of radionuclides described above is a basic requirement for taking effective countermeasures against contamination buildup. Unfortunately, the current state of knowledge on the mechanisms of BWR contamination buildup is not yet as complete as in the PWR case (see Section 4.4.3.). In addition, similar to the PWR situation, cobalt transport and deposition in a BWR is a complex chemical reaction which can be affected by many parameters. This is an essential reason for the considerable variation in the radiation dose levels frequently observed between different plants, which often cannot be explained in a simple manner by differences in design and/or operation. 

As with PWRs, several attempts have been made to describe activity and contamination buildup in BWR plants by computerized models. These models are essentially based on materials balances for the iron transport and on materials and activity balances for the cobalt transport. The reaction rates and the reaction orders needed for the calculations in the partly very complex models are in most cases empirical values or even assumptions. The principles of some of the models have been outlined e. g. by Ishigure (1987) and by Alder et al. (1992). 

The General Electric model (Lin et al., 1981) is a comprehensive analytical description of the activity transport as well as of the activity buildup. Iron transport and cobalt transport are treated in separate sets of equations of balance. The block diagram of Co/ Co transport is shown in Fig. 4.51. In this model, several interactions are considered to exist between dissolved ions and corrosion product particles, including adsorption of ionic species onto the surfaces of the particles. Moreover, both particulate and dissolved species are assumed to be deposited onto the surfaces of the fuel rods, with corrosion product particles playing an important role in the deposition of the ionic species. The fuel rod deposits are assumed to consist of two layers, loosely-adherent and tenacious ones, and a certain amount... 

Figure 4.51. Block diagram of the General Electric model for cobalt transport (Continuous lines Co transport Broken lines Co transport)...

EPRI (Electric Power Research Institute) Proceedings of the BWR Radiation Control and Radwaste Processing Seminar. Report EPRI NP-2417-LD (1982) Chapter 16 Hemmi, Y, Kamata, T., Nakayama, Y, Tani, A., Morikawa, Y, Sato, Y, Nagao, H., Sasaki, S., Sato, Y, Kuba, M., Kakefuda, M. BWR cobalt transport model. Proc. 2. BNES Conf Water Chemistry of Nuclear Reactor Systems, Bournemouth, UK, 1980, p. 319-326... 

The amount of each element required in daily dietary intake varies with the individual bioavailabihty of the mineral nutrient. BioavailabiUty depends both on body need as deterrnined by absorption and excretion patterns of the element and by general solubiUty, and on the absence of substances that may cause formation of iasoluble products, eg, calcium phosphate, Ca2(P0 2- some cases, additional requirements exist either for transport of substances or for uptake or binding. For example, calcium-binding proteias are iavolved ia calcium transport an intrinsic factor is needed for vitamin cobalt,... 

Conventional Transportation Fuels. Synthesis gas produced from coal gasification or from natural gas by partial oxidation or steam reforming can be converted into a variety of transportation fuels, such as gasoline, aviation turbine fuel (see Aviation and other gas turbine fuels), and diesel fuel. A widely known process used for this appHcation is the Eischer-Tropsch process which converts synthesis gas into largely aHphatic hydrocarbons over an iron or cobalt catalyst. The process was operated successfully in Germany during World War II and is being used commercially at the Sasol plants in South Africa. 

Similarly, when catalyzed the reaction rate decreases significantly as a function of pH level. The optimum reaction pH level is approximately 9.5 to 10.5. Iron, and especially copper, in the boiler may act as adventitious catalysts. However, as metal transport polymers are frequently employed, iron, copper, or cobalt may be transported away from contact with sulfite, and thus are not available for catalysis. (This may be a serious problem in high-pressure units employing combinations of organic oxygen scavengers and metal ion catalysts.)... 

Nickel is required by plants when urea is the source of nitrogen (Price and Morel, 1991). Bicarbonate uptake by cells may be limited by Zn as HCOT transport involves the zinc metal-loenzyme carbonic anhydrase (Morel et al., 1994). Cadmium is not known to be required by organisms but because it can substitute for Zn in some metalloenzymes it can promote the growth of Zn-limited phytoplankton (Price and Morel, 1990). Cobalt can also substitute for Zn but less efficiently than Cd. 

Catalysts from active carbon additionally activated with cobalt- or iron- phthalocyanines are also studied [7], The results show that at current densities up to 50 mA/cm2, the polarization of the air electrodes with catalyst from active carbon promoted with FePc is lower than that of the electrode with catalyst from active carbon promoted with CoPc. At higher current density the polarization of the electrode with catalyst from active carbon promoted with CoPc is lower, which is probably connected to the lower transport hindrances, due to the more favorable structure of this catalyst. 

It does not involve the concentration of catalyst in the film, since it represents the pseudo-first-order addition of the substrate, O2, on the active form of the catalyst [i.e., the cobalt(II) porphyrin]. The characteristic currents for electron transport and substrate diffusion are the same as previously [equations (4.29) and (4.30), respectively]. 

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