Uranium fluoride complexes

The rate (kinetics) and the completeness (fraction dissolved) of oxide fuel dissolution is an inverse function of fuel bum-up (16—18). This phenomenon becomes a significant concern in the dissolution of high bum-up MO fuels (19). The insoluble soHds are removed from the dissolver solution by either filtration or centrifugation prior to solvent extraction. Both financial considerations and the need for safeguards make accounting for the fissile content of the insoluble soHds an important challenge for the commercial reprocessor. If hydrofluoric acid is required to assist in the dissolution, the excess fluoride ion must be complexed with aluminum nitrate to minimize corrosion to the stainless steel used throughout the facility. Also, uranium fluoride complexes are inextractable and formation of them needs to be prevented. 

A recent study of the alkali metal/uranium fluoride complex systems has shown that KriUFo, K3UF7, and K UFs are isomorphous (99), the crystal symmetry being unaffected by the fluoride ion absences. The structure of K PaFy has been determined only recently (39), and it has been shown that each protactinium atom is surrounded by nine fluorine atoms in what is effectively a trigonal prism with three added equatorial fluorine atoms the PaFo groups are linked in infinite chains by two fluorine bridges. 

Formation of Uranium Fluoride Complex by Addition of Fluoride Ion to Molten NaCl-CsCl Melts... 

Assay of beryllium metal and beryllium compounds is usually accomplished by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryllium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryllium content of the sample is calculated from the titration volume. Standards containing known beryllium concentrations must be analyzed along with the samples, as complexation of beryllium by fluoride is not quantitative. Titration rate and hold times are critical therefore use of an automatic titrator is recommended. Other fluoride-complexing elements such as aluminum, silicon, zirconium, hafnium, uranium, thorium, and rare earth elements must be absent, or must be corrected for if present in small amounts. Copper—beryllium and nickel—beryllium alloys can be analyzed by titration if the beryllium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

Chloride complexation studies of the actinide ions An3+, An4+, An02, and AnO + (An = U, Np, Pu) were reported in several comprehensive reviews [293-295], More recent investigations on aqua and chloro complexes of U02+, NpOz+, Np4+, Pu3+, etc., by x-ray absorption fine structure spectroscopy (XAFS) were reported [296,297]. In particular, it was established for U(IV) and Th(IV) aqua ions and fluoride complexes that both M(IV) aqua ions are 10-coordinate with M — O bond distances for U(IV) and Th(IV) of 2.42 0.01 A and 2.45 0.01 A, respectively [297], Physical and chemical studies of uranium aqueous complexes are reported [298,299a], A series of articles is dedicated to specific sequestering agents for the actinides [299b-e],... 

Table IV. Some Alkali Fluoride Protactinium ( V ), Uranium ( V ), Neptunium(V), Plutonium(V) Fluoride Complexes"...

Table 22 Uranium(IV) fluoride complexes produced by hydrothermal syntheses.

Binary halides. A number of homoleptic halides of pentavalent protactinium, uranium, and neptunium have been reported. In particular, the fluoride complexes AnFs are prepared by high... 

Uranium tetrafluoride is a key intermediate in the production of thermal reactor fuels. It may be prepared directly from uranyl solutions by reduction of the U to U and addition of HF to precipitate UF4. A number of processes have been developed to produce UF4 by this wet route, which may be used to produce UF4 at the ore processing site. These employ iron, S02/Cu or electrolysis for the reduction step, the latter being preferred since it introduces no contaminants into the solution. The reduction of u in various media has been studied to assess the effect of complexation on the reduction reaction. The standard potential for the reduction of U02 to in 1 M HCIO4 has been given as +0.32 V. " The overall formation constants of fluoride complexes in 1 M NaCl were found to be log 82= 13.12, logj83 = 17.46 and log/84 = 21.8. Although wet processes have been developed as a short cut to UF4, the most widely used process at present involves dry processing. 

Calcium(II), which shows no appreciable complexing, has a distribution coefficient of 147 in 0.5 M perchloric acid and 191 in 0.5 M hydrochloric acid. Strelow. Rethc-meyer, and Bothnia [10] also reported data for nitric and sulfuric acids that showed complexation in some cases. Mercury(II), bismuth(III), cadmium(II), zinc(II), and lead(II) form bromide complexes and are eluted in the order given in 0.1 to 0.6 M hydrobromic acid [11]. Most other metal cations remain on the column. Aluminu-m(III), molybdenum(VI), niobium(V), tin(IV), tantalum(V), uranium(VI), tung-sten(VI), and zirconium(IV) form anionic fluoride complexes and are quickly eluted from a hydrogen-form cation-exchange column with 0.1 to 0.2 M HF [12]. 

ABSOLUTE ALCOHOL or ABSOLUTE ETHANOL (64-17-5) Forms explosive mixture with air (flash point 55°F/13°C). Reacts, possibly violently, with strong oxidizers, bases, acetic anhydride, acetyl bromide, acetyl chloride, aliphatic amines, bromine pentafluoride, calcium oxide, cesium oxide, chloryl perchlorate, disulfuryl difluoride, ethylene glycol methyl ether. Iodine heptafluoride, isocyanates, nitrosyl perchlorate, perchlorates, platinum, potassium- er -butoxide, potassium, potassium oxide, potassium peroxide, phosphonis(III) oxide, silver nitrate, silver oxide, sulfuric acid, oleum, sodium, sodium hydrazide, sodium peroxide, sulfmyl cyanamide, tetrachlorosilane, i-triazine-2,4,6-triol, triethoxydialuminum tribromide, triethylaluminum, uranium fluoride, xenon tetrafluoride. Mixture with mercury nitrate(II) forms explosive mercury fulminate. Forms explosive complexes with perchlorates, magnesium perchlorate (forms ethyl perchlorate), silver perchlorate. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

---