![]() In the DRE (see Section 2) the fission products were adsorbed in activated carbon delay beds housed in water-cooled tubes. The adsorption beds have long contact time allowing the radioactive krypton and xenon gases opportunity to decay. Nuclear grade activated carbons are prepared from coconut shell or coal-based precursors and are highly microporous. Because methyl iodide is less readily adsorbed than iodine under the conditions of high humidity frequently encountered in reactor, the carbon is impregnated with potassium iodide, potassium triiodide, or tiiethylenediamine. Therefore, these gasses are trapped in activated carbon beds to reduce their concentration in the coolant gas. Accidental leakage of these gasses could occur from the reactor core or primary coolant circuit during operation. Gaseous fission products are produced during reactor operation, notably iodine (in elemental form and as methyl iodide), krypton, and xenon. ![]() BURCHELL, in Carbon Materials for Advanced Technologies, 1999 5.1 Activated carbon ![]() The mechanisms which govern radionuclide retention in glass alteration phases are sorption, coprecipitation and precipitation (see below and page 76). This is valid particularly for anionic species while cationic species are strongly retained in the alteration products. The radionuclides which were initially incorporated in the glass are partly released upon glass dissolution in groundwater. Glass dissolution leads to the formation of secondary alteration products such as surface gels, clay minerals, zeolites, oxides, etc. Redox conditions have little or no effect on glass dissolution. Sorption and precipitation of dissolved silica onto container corrosion products, bentonite and/or host rock may maintain for a certain time a relatively high dissolution rate of glass, but even in contact with near field materials very low long-term dissolution rates are obtained. The aqueous silica concentration is about 60 mg/L. For the French nuclear glass R7T7 the long-term corrosion rates are about 10 −4–10 −5 g/m 2/d at 90☌ ( Ferrand et al., 2006). Glass dissolution rates mainly depend on silica concentration in solution. Containers will have to prevent water contact to the waste glass for thousands of years but inevitably, after container breach by corrosion and mechanical failure, water contact leads to slow glass dissolution. Grambow, in Radionuclide Behaviour in the Natural Environment, 2012 Nuclear waste glassesįission products and minor actinides resulting from spent fuel reprocessing are being vitrified for final disposal. Thus, fuel particle dissolution kinetics controlled the release of fission products to the environment ( Kashparov et al., 2004 Kashparov et al., 1999 Kruglov et al., 1994 Sokolik et al., 2001 Uchida et al., 1999).Ī. Fission products were effectively sequestered – for example, little downward transport in soil profiles and little biological uptake – until dissolution of the fuel particles occurred and the fission products were released ( Baryakhtar, 1995 Konoplev and Bulgakov, 1999 Konoplev et al., 1992 Petryaev et al., 1991). ![]() As discussed in more detail later, at Chernobyl, the majority of fission products was released in fuel particles and condensed aerosols. For radioactive contaminants released as particulates – ‘hot particles’ – radionuclide transport is initially dominated by physical processes, namely, transport as aerosols ( Wagenpfeil and Tschiersch, 2001) or as bedload/suspended load in river systems. While fission product mobility is mostly a function of the chemical properties of the element, the initial physical form of the contamination can also be important.
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