302 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Transuranic Qiemistry in Soil 



Sources of the Transuranic Elements 



The transuranic elements of principal importance in the nuclear fuel cycle (plutonium, 

 americium, curium, and neptunium) can enter the soil through several avenues (Vaughan, 

 Wildung, and Fuquay, 1976), including (1) fallout from atmospheric testing, (2) possible 

 escape of airborne particulates and liquid effluents during reprocessing of spent fuels and 

 fuel fabrication, and (3) leaching from waste-storage facilities. The major sources of the 

 transuranic elements can be classified according to expected initial solubility in soil: 

 Insoluble source terms 



MOx + L ^ ML 



Soluble source terms 

 Hydrolyzable 



(1) M(N03)x + L + H2 



MOx • nH2 



or 

 . M(OH)x 



l + ML 



Nonhydrolyzable 



(2) M(N03)x + L + H2 O ^ MO; + ML 



Organic complexes 



(3) MLi +L2 +H2 0^MLi +ML2 + MLi,2 



MLi + L2 + H2 O ^ as m (1 ) or (2) 



where M represents transuranic elements and L represents inorganic and organic ligands 

 capable of reacting with transuranic elements and forming soluble or insoluble products. 

 Particulate oxides of the transuranic elements initially can be expected to be largely 

 insoluble in the soil solution. Ultimately, solubility is expected to be a function of the 

 composition, configuration, and equivalent diameter of the particle as well as soil 

 properties and processes. Oxide particles of the highest specific activity and containing 

 the highest concentrations of impurities in the crystal lattice may exhibit the greatest 

 solubility. The combination of configuration and equivalent diameter as reflected in 

 surface area exposed to solution will be the other main factor governing oxide solubility. 

 Once solubilized, the transuranic elements will be subject to the chemical reactions 

 governing soluble salts. Hydrolyzable transuranic elements entering the soil in acid 

 solutions sufficiently concentrated to maintain soluble ions can be expected to be rapidly 

 insolubilized as a result of hydrolysis on dilution and subsequent precipitation on particle 

 surfaces. These include Pu(in, IV, and VI), Am(III), Cm(III), and Np(III, IV, and VI). 

 Conversely, transuranic elements not subject to marked hydrolysis can be initially more 

 soluble. These include Pu(V) and Np(V). Immobilization of these chemical species (PuO: 



