Radiolysis amide extractants

Different studies indicate that diluents can inhibit or sensitize an extractant s radiolysis. For example, in the cases of alkyl phosphates, amide extractants, or crown ethers, aromatic additives act as protectors (39, 84, 88, 90, 199, 254, 298), while saturated hydrocarbons often sensitize the decomposition of the extractant (90, 182, 183, 199, 299). Figure 8.18 illustrates this sensitization effect of n-dodecane on various oxygen-donor ligands (diglycolamide, malonamide, and monoamides) (199). 

The selection of a suitable diluent is important to limit radiolytic degradation. Diluents currently used in nuclear applications are hydrocarbons, despite their well-known sensitization effect on radiolysis, as mentioned for alkylphosphates or amide extractants (90, 182, 183, 199), and as discussed in Section 8.4.2. To avoid this negative effect or to enhance the solubility of ligands and metallic complexes, other diluents have been selected and their influence on degradation investigated. 

Unlike the extractant TBP (26, 27, 98), the radiolysis yields strongly depended on the nitric acid concentration (188, 189) after irradiation of DEHHA in TPH in the presence of nitric acid aqueous phase, the G(-amide) = 3.6 and 0.9 for 4 and 0.5 mol L 1 HN03, respectively. 

The extraction of Th(IV) was not affected by the gamma radiolysis over the entire range from 0 to 1 MGy for both symmetrical and N-methyl amides (192). 

Recently, the primary processes were investigated using pulse radiolysis with two extractant-alkane systems (182, 292). Transient optical absorption spectra proved that in the presence of ligands like TODGA, the excited species of -dodecane (singlet excited state and radical cation) disappeared immediately. Results showed that an energy transfer occurred from the excited alkane to the extractant molecule (TBP, TOPO, or amide), which constituted an additional decomposition route, as described in the following set of reactions ... 

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