Extractants radiolytic

TBP is a sufficiently powerful extractant for actinides that it may be used in diluted form. Dilution improves the hydrodynamic properties of the solvent, allowing more complete and rapid phase disengagement. Typically concentrations of 20-30 v/o TBP in OK are used in process flowsheets. Although TBP is relatively stable as an extractant, radiolysis does lead to the formation of some acidic phosphate esters, HDBP and H2MBP, which can impair process performance.289 An aqueous alkali wash of the recycled solvent is usually carried out to remove those by products. Radiolytic degradation of the diluent in the presence of nitric acid can result in the formation of hydroxamic acids,290 which can lead to fission product retention by the organic phase. Again the solvent wash is used to prevent the accumulation of such species. A comprehensive account of the industrial utilization of TBP has recently been published.291... 

Berthon, L., Morel, J.M., Zorz, N. et al. 2001. DIAMEX process for minor actinide partitioning Hydrolytic and radiolytic degradations of malonamide extractants. Sep. Sci. Technol. 36 (5 6) 709-728. 

Sugo, Y., Sasaki, Y., Kimura, T., Sekine, T. 2007. Attempts to improve a radiolytic stability of amidic extractants. GLOBAL 2007, Boise, ID, September 9-13, pp. 1870-1873. 

The radiolytic and chemical degradation of TBP gives rise to monobu-tylphosphoric acid (MBP) and DBP, which are powerful extractants under low acidic conditions. As stripping in the PUREX process is carried out under such... 

Hydrolytic and radiolytic degradation of TAP solution in normal paraffinic hydrocarbon (NPH) in the presence of nitric acid was investigated. Physicochemical properties such as density, viscosity, and phase-disengagement time (PDT) were measured for undegraded and degraded solutions (197). The variations in these parameters were not very different from those obtained with degraded TBP. Thus, the hydro-dynamic problems expected during the solvent-extraction process with TAP would be similar to those encountered with TBP/NPH system. The influence of chemical... 

Since the pioneering work of Siddall, /V./V-dialkyl amides have been evaluated extensively as alternative extractants to TBP (200, 201). The salient features of amides as extractants are (i) low volume of secondary waste generated (completely incinerable), (ii) innocuous nature of chemical and radiolytic degradation products (better decontamination from fission products andregeneration/clean up easier), (iii) low aqueous-phase solubility, (iv) final U and Pu products streams are free of P contamination, and (v) ease of synthesis. However, LOC values of U and Pu as well as viscosity are... 

Cames, B., Caniffi, B., Rudloff, D. 2008. Radiolytic and hydrolytic stability of extractant molecules. ATALANTE 2008 Nuclear Fuel Cycles for a Sustainable Future, May, Montpellier, France. 

The first project, gathering eight teams from six EC countries where more than 140 new extractants were prepared and studied, not counting all the precursors and intermediates. Tests carried out with these compounds on simulated and real waste showed the excellent chemical and radiolytic performance of calixarene derivatives. 

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 radiolytic. 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 II-, OH-, solvated electrons, H2, or H202), which recombine in molecular products shared between the two phases. 

Di(2-ethylhexyl) phosphoric acid (HDEHP) is an extractant molecule used for An(III)/Ln(III) separation. Used in TALSPEAK-type processes in a mixture with TBP, or in the DIAMEX-SANEX process in a mixture with a malonamide (154-157), it has also been proposed, in a mixture with TBP, to remove strontium from PUREX acid waste solution in the Hanford B plant (158). Therefore, numerous studies have focussed on the radiolytic degradation of HDEHP and its effects on the extraction of Sr(II), lanthanides(III), and actinides(III) (10, 158-163). 

Concerning strontium extraction, the principal radiolytic effect was a two- to threefold decrease (158). Schultz explained this effect by the polymerization of HDEHP with H2MEHP via hydrogen bonding, making HDEHP molecules either unavailable or less available for binding with strontium. According to Tachimori (163), the... 

In a recent study, Retegan compared the radiolytic stability of C5-BTBP and CyMe4-BTBP in hexanol or in cyclohexanone (242). No protective effect of a cyclic diluent was observed on europium extraction, whereas surprising results were obtained with americium. The behavior needs to be more precisely defined. 

The crown ethers were investigated mainly for the removal of Sr or Cs from nuclear-waste streams (246-250), and some studies reported their interest as selective extractants of plutonium (251). Different crown ether derivatives with the addition of alkyl chains have been examined, in order to increase the lipophilicity of the molecule and prevent major extractant losses due to high solubility in aqueous phases. These extractants were described as radiolytically resistant, and their stability increased in the order benzocrown > dicyclohexanocrown > crown (44). 

Extraction of U(VI) and Pu(IV) from 1 to 8 mol L 1 HN03 solutions by radiolytically degraded DCH18C6 in toluene was studied (256). A decrease in the distribution ratios for both U and Pu was observed for irradiation in the range 0.010-0.071 MGy, with a higher effect for Pu(IV). For 0.2 mol I. DCH18C6-toluene solution in contact with 3 mol I. nitric acid, D, decreased from 0.21 to 0.12 and /.)hl from 64.3 to 6.42 after a dose of 0.07 MGy. This behavior was explained by both diluent and extractant degradation. 

To limit the radiolytic degradation of extractants, the influences of free-radical inhibitors have been measured. The addition of dimethoxybenzaldehydes (DMBA), particularly 3,5- and 3,4-DMBA, to the PUREX solvent could improve its stability and decrease its contamination (307). DMBA has a double effect, including a protective effect for the excited molecules of TBP (because of its low ionization potential), and the aldehyde radiolysis products could react with the HDBP present and therefore inhibit its complexing properties. 

RELATION BETWEEN THE FORMULATION OF THE SOLVENT AND THE RADIOLYTIC STABILITY OF THE EXTRACTANT... 

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