Activated carbon nuclear applications

Adsorption of Radionuclides. Other applications that depend on physical adsorption include the control of krypton and xenon radionuclides from nuclear power plants (92). The gases are not captured entirely, but their passage is delayed long enough to allow radioactive decay of the short-lived species. Highly microporous coconut-based activated carbon is used for this service. 

The dynamic characteristics of adsorbed molecules can be determined in terms of temperature dependences of relaxation times [14-16] and by measurements of self-diffusion coefficients applying the pulsed-gradient spin-echo method [ 17-20]. Both methods enable one to estimate the mobility of molecules in adsorbent pores and the rotational mobility of separate molecular groups. The methods are based on the fact that the nuclear spin relaxation time of a molecule depends on the feasibility for adsorbed molecules to move in adsorbent pores. The lower the molecule s mobility, the more effective is the interaction between nuclear magnetic dipoles of adsorbed molecules and the shorter is the nuclear spin relaxation time. The results of measuring relaxation times at various temperatures may form the basis for calculations of activation characteristics of molecular motions of adsorbed molecules in an adsorption layer. These characteristics are of utmost importance for application of adsorbents as catalyst carriers. They determine the diffusion of reagent molecules towards the active sites of a catalyst and the rate of removal of reaction products. Sometimes the data on the temperature dependence of a diffusion coefficient allow one to ascertain subtle mechanisms of filling of micropores in activated carbons [17]. 

Nuclear applications of nanocapsules are related to the emitting physical properties of the encapsulated material. Emitted radiation can be electromagnetic of high energy (y), electrons or positrons (/3), alpha particles (" He nucleus), or fission products [67]. These emitters can be in themselves radioactive or can be activated by a nuclear reaction, usually a neutron capture. The particular advantage of carbon nanocapsules in nuclear applications is related to the protective characteristics that the carbon capsule confers to the interior product. Experiments on irradiation of fullerenes have shown that knocked carbon atoms from one cage are foimd in another fuUerene and even form dimers and trimers by a recoil-implantation mechanism [68]. The observed major damage of capsules in nanoencapsulated molybdenum irradiated in a nuclear reactor was produced by... 

Nuclear applications of carbon nanocapsules with radioactive materials inside are in the very early steps of investigation. Because of time-consumming experiments, post-irradiation analysis, protocols, complex interdisciplinary work, and the usual requirement of big facilities to be employed, make advances very punctual. Feasibility studies are usually done to a deeper stage than in other areas of activity to balance research investment. Surely, results wiU be as promising as in other disciplines of nanotechnology. 

Radioactive iodine resulting from nuclear reactor operations is commonly adsorbed on activated carbon. Problems encountered in this application include weathering by humid air, the presence of a portion of the iodine in compounds such as methyl iodide which are not as readily adsorbed, and the effects of radiation. At the Savannah River Plant (SRP) activated carbon beds must be replaced after 3 to 5 years to ensure that iodine adsorption efftciency meets the required design level (99.85% removal (Milham, 1968). In this plant, Bamebey-Cheney Type 416 carbon is used to purify a flow of 100,000 cfm of air. The effect of radiation on the adsorption of iodine and methyl iodide is described by Jones (l%8). 

Today s rapidly increasing activities on hydrogen focus mostly on vehicle applications and less on stationary applications. For fuel cells, stationary applications are also relevant, but natural gas will be the dominant fuel here. The dominance of the transport sector is also reflected in the hydrogen roadmaps developed, among others, in the EU, the USA, Japan, or at an international level. Whereas in the beginning, onsite or decentralised production options based on fossil fuels or electricity are seen as the major option for hydrogen production, later on central production options will dominate the market. Here, several options could play a role, from coal, with carbon capture and sequestration, through natural gas and renewables (wind, biomass) to nuclear. A C02-free or lean vision can be identified in every roadmap. The cost... 

C-Labelled phosgene is a useful material in radiopharmaceutical and nuclear medical applications, since it combines the radiophysical properties of C with the extensive reaction chemistry of phosgene to permit the rapid synthesis of a wide range of biologically-active materials with radiochemical labels. Carbon-11 is a short-lived positron-emitting radionucleide, useful for in vivo measurements with positron emission tomography (PET) [519], Because of... 

Oxygen. Analyses are ordinarily made by vacuum fusion with Fe or Pt [22,23,27] or by inert gas fusion [28]. The sample is dissolved in the molten metal saturated with carbon in a graphite crucible at 1900°C and the evolved CO converted to CO2 in a CuO column and measured gas-volumetrically. More reproducible results are said to be obtained by neutron activation analysis for oxygen. With this method the sample is exposed a few minutes to 14 MeV neutrons to activate the oxygen by the nuclear reaction 0(n,Y) 0 and the amount of oxygen is obtained from the 0 activity having the half life of ty = 29.1 s [29] by comparison with that of a standard. The technique of isotopic dilution which has been used to analyze for oxygen in Ti should be applicable too [30]. 

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