Neptunium thermodynamic properties

Americium. The low solubilities and high sorption affinity of thorium and americium severely limit their mobility under environmental conditions. However, because each exists in a single oxidation state—Th(IV) and Am(III)— under environmentally relevant conditions, they are relatively easy to study. In addition, their chemical behaviors provide valuable information about the thermodynamic properties of trivalent and tetravalent species of uranium, neptunium, and plutonium. 

Rand, M. H., Fuger, J., The thermodynamic properties of the transuranium halides Part 1, Neptunium and plutonium halides, ITU, European Commission Joint Research Centre report. Report 17332 EN, (2000). Cited on pages 500, 513, 522, 528, 546, 547. 

Duplessis, J. and Guillaumont, R. (1977) Hydrolyse du neptunium tetravalent. Radiochem. Radioanal. Lett, 31, 293-302. Edelstein, N., Bucher, J., Silva, R.J. and Nitsche, H. (1983) Thermodynamic Properties of Chemical Species in Nuclear Waste. Technical Report, ONWI-399 Lawrence Berkeley Laboratory, 125 pp. Ekberg, C., Brown, P., Comarmond, J., and Albinsson, Y. (2001) On the hydrolysis of tetravalent metal ions. Mater. Res. Soc. Symp. Proc., 663, 1091-1099. 

Plutonium and neptunium nitrides were studied for the application to advanced fast breeder reactor (FBR) fuels. Details on the application of nuclear fuels is available in the reference (Matzke 1986). Fundamental properties of these plutonium and neptunium compounds are reviewed in the Chemical Thermodynamics of Neptunium and Plutonium (Lemire et al. 2001) issued by OECD/NEA (Organization for Economic Co-operation and... 

The quite similar chemical properties of uranium and the transuranium elements are the reason for their presence in the irradiated fuel as thermodynamically stable double oxides. According to the redox potential of the fuel matrix, it has to be assumed that neptunium and plutonium will appear in their most stable oxidation state +4. Due to their ionic radii, which are very similar to that of U(IV), both NpO and Pu02 will form mixed crystals with UO2. The type and the properties of the crystal lattice remain essentially unchanged only the dimensions of the elementary cell decrease from 0.5468 nm (5.468 A) in pure UO2 to 0.5466 nm (5.466 A) at 1% plutonium content. This means that neptunium and plutonium will remain at the positions in the irradiated fuel where they were formed the same behavior is to be expected for the higher transuranium elements as well. 

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