Trace I mpurity Ana lysis of Plutonium-U ra n ium-Zirconiu m Alloys by Anion Excha nge-Pa rtition Chroma tog ra phy SIR: Anion exchange-partition chromatography has been applied previously (3) to the trace impurity analysis of binary thorium-uranium and ternary plutonium-thorium-uranium alloys. The present paper describes an extension of this technique to the determination of trace metal contaminants in ternary plutonium-uranium-zirconium alloys. These materials are presently under investigation ( I ) as possible fuels in fast breeder reactors; thus their characterization as to impurity content is of considerable interest. Since a large number of samples were not anticipated, analysis by direct excitation was not feasible because the variable matrix composition (plutonium 18.5 to 27.1%; uranium 67.4 to 71.6y0; zirconium 2.4 to 1.4.1%) precluded the preparation of reliable standards. A basic feature of the method was the adsorption of two matrix components by a mixed organic stationary phase. Optimum composition of the mixture for this application was determined by liquid-liquid extraction experiments with zirconium. EXPERIMENTAL
Materials and Reagents. Anion exchange resin, chromatographic columns, and general laboratory ware were described previously ( 3 ) . Plaskon, Type CTFE 2300, a trifluorochloroethylene polymer, was obtained from Allied Chemical Corp. and used without further treatment. Tri(2-ethylhexy1)phosphate [ T E H P 1, a product of K and K Laboratories, Inc., was washed with 57& sodium carbonate, distilled deionized water, and 8N nitric acid. Di(2-ethylhexyl) hydrogen phosphate [HDEHP], obtained from Distillation Products Industries, was conditioned with 8N nitric acid and used without further purification. The TEHP-HDEHP mixtures were made by volume dilutions of these reagents. A 20-mg./ml. zirconium standard was prepared by dissolution of high purity metal in 8N nitric acid and a
minimum amount of 2N hydrofluoric acid. Column Preparation and Separation. The previously described (3)
column preparation technique was found to be satisfactory. However, because of the higher percentage of uranium in the alloy matrix, it was necessary to increase the organic support phase. This was prepared by stirring 3 to 5 grams of Plaskon polymer with 4 ml. of a 95% TEHP-5% HDEHP mixture until the resin was uniformly coated. The chromatographic column had the following approximate dimensions: A 1-cm.-high bed of settled anion resin lower phase, a 10-cm.-high TEHP-HDEHP-coated Plaskon middle phase, and a 3-cm.-high bed anion resin upper phase. Before use, the column was thoroughly washed with 1N nitric acid to ensure the removal of common blank impurities and finally conditioned with 8'47 nitric acid. A 0.20- to 0.30-gram alloy sample was dissolved in 8N nitric acid. Heating and the dropwise addition of 2N hydrofluoric acid hastened dissolution. The cooled sample solution was added to the chromatographic column and the nonabsorbed impurities were eluted with approximately 40 ml. of 8N nitric acid. The flow rate was kept between 0.5 to 1 ml. per minute, since a faster elution resulted in an excessive spreading of the yellow uranium(V1) band. The columns were prepared for reuse by stripping of the ternary matrix with a mixture of 0.4N nitric-0.02N hydrofluoric acid (40-80 ml.) until the pink plutonium band completely disappeared from the organic phase. Elution was continued with a 0.5'47 nitric-3N hydrofluoric acid mixture to remove any remaining uranium and zirconium (40 ml.). Binary uraniumzirconium alloys were eluted with the latter stripping solution. Before reuse for other separations, the column was washed with 1N and conditioned with 8N nitric acid. Concentrations of impurity elements were determined by the copper spark spectrographic method (2). Both visual and densitometric evaluation of line intensities were utilized.
Table 1. Recovery of Added Impurities from a 27.1% Plutonium-68% Uranium-4.9% Zirconium Alloy, p.p.m.
Element A1 Cr
Impurities Initial A m 94 83 402 36 52
100 100 100 100 100
Fe Mn Ni a Based on 6 determinations.
Total Theoretical Found 194 183 502 136 152
Liquid-Liquid Extraction. The distribution ratio, D , of zirconium(1V) between 8 N nitric acid and variable organic phase compositions was determined by standard liquid-liquid extraction techniques. The phase volumes were kept constant a t 10 ml. and the equilibration time was 2 minutes. The concentration of zirconium in the aqueous phase after extraction was determined spectrographically by the copper spark method, using titanium (5 pg./ml.) as the internal standard in the construction of a working curve.
208 198 538 128 152
Rel. std. dev.a zt4 f 2
zt6 f10 *3
Table II.
Element A1 Cr
RESULTS
The precision and accuracy of the proposed separation procedure was determined by repeated analyses of a representative ternary plutonium-uranium-zirconium alloy. Quantitative recoveries of five common impurities were verified by the densitometric copper spark method, using cobalt (10 pg./ml.) as an internal standard. The results are shown in Table I. Table I1 contains data obtained by repeated analyses of a synthetic uranium-zirconium alloy. The latter results serve to show that the ternary alloys of higher purity than presently available could be analyzed with adequate precision by the discussed method. The behavior of additional elements on the chromatographic column was evaluated by visual spectrographic determination of added impurities. Duplicate 40-ml. dutions indicated quantitative recoveries of the following elements a t concentrations of 1 to 100 Hg.: Ag(I), As(V), Ba(II), Be(II), B(III), Ca(II), Cd(II), Co(III), Cu(II), Cs(I), Ga(III), In(III), K(I), Li(I), Mg(II), Mo(VI), Na(I), Pb(II), Rb(I), Rh(III), Ru(IV), Sc(III), Sr(II), Sn(IV), Te(IV), Ti(IV), V(V), Y(III), Zn(II), and the rare earths. Limits of detection were comparable to those reported previously (3). The distribution ratios found for zirconium(1V) in TEHP and in TEHP mixtures containing variable amounts of HDEHP are shown in Table 111. The
Recovery of Added Impurities from a 93.8% Uranium-6.2% Zirconium Alloy, p.p.m.
Impurities Initial Added 4 2
13 13
Fe 14 13 Mn 3 13 Ni
