Solvents radiolytic degradation

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... 

Tripathi, S.C., Sumathi, S., Ramanujam, A. 1999. Effects of solvent recycling on radiolytic degradation of 30% tributyl phosphate- -dodecane-HN03 system. Sep. Sci. Technol. 34 (14) 2887-2903. 

Zhang, P, Song, C.L., Liang, J.F., Xin, R.X. 2003. Identification of radiolytic degradation products of y-irradiated 30% trialkylphosphine oxide-kerosene solution. Solvent Extr. IonExeh. 21 (1) 91-108. 

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... 

Venkatesan, K.A. Robertselvan, B. Antony, M.P. Srinivasan, T.G. Vasudeva Rao, PR. Physiochemical and plutonium retention properties of hydrolytic and radiolytically degraded tri- -amylphosphate, Solvent Extr. Ion Exch. 24 (2006) 747-763. 

The radiolytic degradation of solvents was usually performed by irradiation of synthetic solutions rather than industrial samples. In more than 90% of studies, samples were exposed to y-irradiation with a 60Co source, and sometimes with a 137Cs... 

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. 

Chiariza, R., Horwitz, E.P. 1986. Hydrolytic and radiolytic degradation of octyl(phenyl) butyl carbamoylmethyl phosphine oxide and related compounds. Solvent Extr. Ion Exch. 4(4) 677-723. 

A well-designed Purex plant aims for as complete recycle of solvent as possible, to minimize costs of solvent makeup and disposal. Solvent from the uranium purification section usually contains so few contaminants or degradation products that it can be reused a number of times without cleanup. On the other hand, solvent that has processed solutions containing hi activity of fission products and plutonium carries traces of these contaminants, uranium, nitric acid, dibutyl phosphate, and other radiolytic degradation products of TBP and dodecane. Uranium and plutonium should be recovered because of their value. Fission products should be removed to prevent product contamination in later cycles. Dibutyl phosphate should be removed because it forms strong complexes with tetravalent zirconium and plutonium that would impair ability of the solvent to reject zirconium and separate plutonium from uranium. 

Conditions for isolation of cobalt 60 radiolytic degradation products as well as paths and schemes of degradation are described. For prednisolone methylchloride was used as enrichment solvent, a HPLC Brownlee RP 18 column C 18 bonded phase and a mobile phase of methanol-water, 55 45 were used. The rate of radiolytic degradation in prednisolone is given as 0.7 %/Mrad (64). 

Radioprotection. The processes of crosslinking and degradation observed in polymers irradiated in the pure state can also be observed in polymers irradiated in solution. The presence of a solvent can intervene in the reaction in several ways thus it allows increased polymer mobility, and some of the radiolytic products of the solvent may react with the polymer or with the polymer radicals, etc. The polymer-water system is of particular interest in that it provides a simple model for some radiobiological systems and can be analyzed far more readily. 

Stieglitz, L., Becker, R. 1982. Chemical and radiolytic solvent degradation in the PUREX process, in Nukleare Entsorgung Nuclear Fuel Cycle-, Baumgartner, F., Ebert, K., Gelfort, E., Lieser, K.H. Eds. Verlag-Chemie Weinheim, Deerfield Beach, EL, Basel, 333-350. 

Gas chromatography (GC) with an infrared (IR) detector was introduced as a method to detect volatile radiolytic products, some of which were hypothesized to be responsible for the bad smells emanating from irradiated drugs. Thiocyanic acid was held responsible, for example, for the sulfurous smell in irradiated ampicillin. The head-space (HS) injection technique for GC and the on-line MS detection allowed new approaches to detect radiosterilization [12]. Many volatile radiolytic products were identified from the mass spectral libraries. Some ofthe compounds identified such as aldehydes, esters and sulfides were quite malodorous. A few of the volatile radiolytic products came from the degradation of drug molecules by the ionizing radiation, whereas residual solvents played a key role in the formation of other volatile radiolytic products. 

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