[en] Solubilities of key solid compounds that are either present in the waste form or can readily precipitate from waste package leachates under repository conditions can be used to set maximum limits on radionuclide concentrations expected in ground water. This is because the solubility limited concentrations are independent of the release scenarios, hydrologic transport characteristics, and absorption-desorption reactions. Some of the important factors that control solubilities are pH, pe, type of solid phase, and nature of complexing ligands in the ground waters. Most of the above factors are affected by radiolysis due to the inherent radiation field of the waste form. Experimental results pertaining to the solubilities of selected Am, U, Np, and Pu compounds and the effects of radiolysis are discussed. These results show that: (1) at expected repository pH and reducing conditions, solubility controlled concentrations of several actinides are low and near acceptable limits, (2) the redox conditions at the waste form-water interface may be very oxidizing due to radiolytic effects, despite the fact that normal repository conditions are assumed to be reducing, (3) additional data on solubility limits and key thermodynamic parameters are needed. 26 references, 4 figures

[en] Precipitation of ²⁴¹Am or ²⁴⁴Cm(55%²⁴⁴Cm) trihydroxides from an aqueous solution yields very small (10 to 20 A in diameter) amorphous particles. Aging of these amorphous particles in water results in the formation of crystalline, rod-like structures of the trihydroxide, which are isomorphous with the hexagonal lanthanide trihydroxides. The lattice parameters and the above crystallization behavior has been reported for ²⁴¹Am(OH)₃ (W.O. Milligan et al., Acta Cryst.; B24:976(1969)). Reported here are similar studies for ²⁴⁴Cm(OH)₃ and the effects of self-irradiation on the crystalline structures of ²⁴¹Am(OH)₃ and ²⁴⁴Cm(OH)₃. The crystallinity of these trihydroxides is destroyed by the alpha particles and/or atom recoil; with ²⁴⁴Cm(OH)₃, the destruction was complete in less than 1 day, while a period of several months was required to observe the same effect for ²⁴¹Am(OH)₃. Lattice parameters for ²⁴⁴Cm(OH)₃ were determined from both X-ray and electron diffraction data. Parameters derived from the X-ray data were generally larger than values from electron diffraction, reflecting that significant crystal damage had taken place in the X-ray samples. The values obtained by electron diffraction are believed to be the better parameters for the ²⁴⁴Cm(OH)₃ preparation and are as follows: a₀ = 6.391 +- 0.002 A and c₀ = 3.712 +- 0.002 A. (author)

[en] A direct speciation of Cm(III) traced in three different Gorleben groundwaters is performed by time resolved laser fluorescence spectroscopy (TRLFS) in very dilute concentrations from 7.8 x 10^-9 mol l^-1 to 6.3x10^-8 mol l^-1, which are below the solubility of Cm(III) at the given aquatic neutral pH. As spectroscopic references, fluorescence spectra are produced for individual hydroxides, carbonates, humate and fulvate of Cm(III). Parallel to the spectroscopic speciation, a thermodynamic speciation is also made based on complexation constants of the predominant aquatic chemical reactions, i.e. hydrolysis, carbonate complexation and humate complexation. The speciation results from thermodynamic calculation and spectroscopy are compared with one another. (orig.)