Chemical behaviour of Np, Pu and Am in various concentrated salt solutions

The chemical behaviour of Np, Pu and Am in various brine solutions has been investigated. The study deals with important basic chemical processes, i.e. solubility, hydrolysis reaction, complexation, redox reaction, colloid generation. The nuclides used are 237Np, 238Pu, 239Pu and 241Am in the form of oxide or/and hydroxide, whereas the saline solution comprises are NaCl-solution of different concentration (0.1 approximately 5 M), Na3γ-salt solution, quinary solution (Q) and saline groundwaters from Gorleben. This paper reports equilibrium solubilities of the nuclides under varying geochemical parameters, Ph, Eh and CO2; thermodynamic constants of hydrolysis reactions of NpO+2, Pu4+, PuO2+2, Am3+ and AmO+2 ions; colloid generation and characterization; speciation; alpha radiolysis effect on dissolution. Complexation and kinetics of redox reactions are only being referred to earlier or on-going works. The speciation has been conducted for relatively higher concentrations by spectrophotometry and for very dilute solutions by laser induced photoacoustic spectroscopy (LPAS). Based on the results from this work and on the literature data, the speciation diagrams of pH-Eh correlation are produced for each element. 66 refs