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Radiolytic degradation is an important aspect to consider when developing a ligand or a complexant for radionuclides. Diglycolamide extractants (DGAs) have been playing an important role in many partition processes for spent nuclear fuel. In particular, the extractant N , N , N ' N '-tetraoctyl diglycolamide (TODGA) has been studied intensively for the purpose of solvent extraction processes such as ARTIST, i-Sanex, EURO-GANEX and EURO-EXAM, which have been developed around the TODGA extractant. For the first time, the radiolytic stability of TODGA was investigated both by in situ alpha irradiation using a macroconcentration of americum(III) and by ex situ gamma irradiation in the presence of a macroconcentration of neodymium(III). It was shown that metal ions complexed in the organic phase protect TODGA from degradation by irradiation and that the degradation was slower using in situ alpha irradiation compared to ex situ gamma irradiation. By comparison to gamma irradiation of Nd-TODGA solution, alpha irradiation of Am-TODGA solutions showed the presence of 2 additional compounds identified as a TODGA molecule with a CC bond and a TODGA molecule with the addition of a NO 3 group. The major degradation products were identified and a degradation schema was proposed. The direct analysis of the solution containing Am(III) or Nd(III) showed that the degradation compounds retaining a diglycolamide skeleton are involved in heteroleptic complexes with TODGA, without a negative impact on An(III) or Ln(III) complexation.

The radiolytic degradation of three N,N-dialkyl amide ligands relevant to nuclear fuel reprocessing was studied. The degradation of these ligands: N,N di-2-ethyhexylbutyramide (DEHBA), N,N di-2-ethyhexylisobutyramide (DEHiBA) and N,N di-2-ethyhexyl-3-dimethylbutanamide (DEHDMBA) was examined to evaluate the effect of the structure on the formation of degradation products as well as to compare alpha induced degradation to gamma induced degradation. In situ alpha radiolysis by introduction of plutonium(iv) as the alpha source in the solution and ex situ gamma radiolysis with 60 Co as the gamma source were compared. Upon identification of the main degradation products, a degradation scheme was proposed. The effects of radiation on the stability of Pu-monoamide complexes were discussed. Theoretical calculations were also performed to determine bond dissociation energy and estimate the relative strength of the bond in the molecule. The results show that neither the type of radiation (alpha vs. gamma) nor the structure modification (introduction of branching on the alkyl chain off the carbonyl carbon) of the molecule significantly impact the formation of degradation products under the conditions studied. Moreover, it was observed that the overall stability of the monoamide remains good and that Pu complexation is not greatly affected by either alpha or gamma irradiation.