Effect of metal complexation on diglycolamide radiolysis: a comparison between <i>ex situ</i> gamma and <i>in situ</i> alpha irradiation

Abstract

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 <i>N</i>,<i>N</i>,<i>N</i>'<i>N</i>'-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 <i>in situ</i> alpha irradiation using a macroconcentration of americum(III) and by <i>ex situ</i> 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 <i>in situ</i> alpha irradiation compared to <i>ex situ</i> 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 NO₃ 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.