Chemistry Reference
In-Depth Information
8.4.1.3 Di(2-Ethylhexyl) Phosphoric Acid..................................... 484
8.4.1.4 Amides ............................................................................... 485
8.4.2 Influence of the Diluent on Degradation .......................................... 485
8.4.3 Influence of an Aqueous Nitric Acid Phase on the Radiolytic
Degradation of TBP.......................................................................... 486
8.4.4 Effect of Inhibitors on TBP Degradation ......................................... 487
8.5 Relation Between The Formulation of the Solvent and the Radiolytic
Stability of the Extractant............................................................................. 488
8.5.1 Modifications to the Extractant Formulae ........................................ 488
8.5.1.1 Presence of Oxygen Atoms................................................ 488
8.5.1.2 Nature of the Substituents.................................................. 489
8.5.2 Composition of the Organic Phase ................................................... 491
8.5.2.1 Choice of the Diluent ......................................................... 491
8.5.2.2 Presence of Additional Ligands ......................................... 491
8.6 Comparison of Extractants' Stability ........................................................... 492
8.7 Conclusions................................................................................................... 493
References.............................................................................................................. 494
8.1 IntRoDUCtIon
The international context for nuclear energy has led the scientific community to draw
up common strategies to plan for new generation reactors. Recycling (individual or by
families) of nuclear materials is a primary objective and requires efficient processes to be
established (
1, 2
). To meet such needs, liquid-liquid extraction remains a favored route.
However, applying extraction by solvent to the nuclear field is not an easy task for
the solvent that undergoes multiple attacks—chemical, thermal, but especially radio-
lytic. This multiplicity is reinforced by the biphasic nature of the chemical system
and the presence of numerous solutes, be it in aqueous or organic phase. Radiolysis
of such a system thus leads to the formation of a multitude of radicals and ionized
species (including the reactive species H
•
, OH
•
, solvated electrons, H
2
, or H
2
O
2
),
which recombine in molecular products shared between the two phases.
The experience gained from the PUREX process, in operation for a half century,
is rich in lessons learned about the potential consequences this can cause:
- Degradation of the solvent formulation (loss of efficiency due both to the
partial disappearance of the extractant at the heart of the process and to the
formation of degradation products that may be competitive);
- Alteration of the physicochemical properties (density, viscosity, interfacial
tension, etc.);
- Modification of the extraction kinetics (presence of precipitates, of inter-
face-active substances, etc.);
- Modification of the redox properties of the metallic ions to be extracted by
reaction with the many radical species present.
During the reprocessing of fuel using the PUREX process, the degradation of tri-
n-
butyl phosphate (TBP) by hydrolysis nevertheless represents an important part, as
