Effects of Reactor Decontamination Complexing Agents on Soil Adsorption of Metals
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posal site licensees must evaluate the impacts of the presence of chelating/complexing agents. Organic complexes have been implicated in several instances as enhancing the mobility of metallike radionuclides such as 60Co, 9 Sr, Pu and Am from shallow-land burial grounds [1,2,3,4,5]. Organic complexes, such as EDTA and picolinic acid, have also been shown to leach from solidified decontamination wastes from nuclear power stations [6,7,8,9,10]. Chemical decontamination solutions are used to remove activated metals and fission products that build-up in nuclear power plant cooling systems. Radioactive species are primarily associated with Fe/Ni/Cr corrosion product films in the cooling system. Removal of these oxide films can significantly reduce the occupational exposure for plant personnel and can improve the thermal hydraulic performance of the cooling system. Three principal chemical decontamination processes are in use: LOMI [11,12,13], CAN-DEREM [14] and CITROX [15]. The LOMI process relies on formic and picolinic acid, while CAN-DEREM relies on citric and EDTA acids, and the CITROX process relies on citric and oxalic acids to dissolve the corrosion films. To address the effects of these complexing agents on the leaching and migration of radionuclides from waste disposed in SLB grounds, the current method of disposal, requires knowledge of 1) the quantities of complexing agents and metal-like contaminants disposed in the burial grounds; 2) the nature of the leaching process; 3) the ability of leached complexing agents to bind released trace radionuclide contaminants, essentially in competition with common cations in the leachate and soil water; 4) the ability of the neighboring soils/sediments to adsorb the complexes, free complexing agents and free metals; and 5) the identification of other processes, 1043 Mat. Res. Soc. Symp. Proc. Vol. 556 0 1999 Materials Research Society
such as biodegradation, that can degrade the released organic complexants. A review of the state of our knowledge on these 5 issues was published in 1996 [16]. One data gap identified in the literature assessment was adsorption of radionuclides in the presence of the key complexing agents mentioned, especially for picolinic acid, onto sediments. This paper presents some of the batch adsorption tests performed for Ni and U in the presence of picolinic acid. Other metals studied include Sm(III)[an analog for trivalent actinides], Th(IV) [an analog for quadravalent actinides], Np(V), and oxidized Pu (starting valence state was (VI)). EXPERIMENTAL METHODS We used two soils in the test matrix. The soils are identified as Milford [Mil] and ferric oxide-coated sand (1.2% wt. Fe) [FeOx], where the brackets denote the short hand used in figure and table captions. The Milford soil is from the Ultisol order collected at a depth of 2 meters from a glacio-fluvial gravel sediment pit exposing the lower Columbia Formation located in Delaware. The ferric oxide-coated sand is a synthetic soil created by using natural quartz sand that was acid washed to remo
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