Determination of Radioactive Zircon ium in Fissioned Plutonium JESSE W. T. MEADOWS and GEORGE M. MATLACK University of California, Los Alamos Scientific laboratory, 10s Alamos,
b Radioisotopes of zirconium, formed in the fission of plutonium, are determined by multiple precipitations of zirconium p-bromomandelate. Tellurium, the only interfering fission product, i s removed by precipitation of carrier tellurium with sulfur dioxide. This also serves to reduce plutonium(1V) to plutonium(lll), which i s not precipitated by p-bromomandelic acid. Four determinations may be made in 5 hours with a coefficient of variation of 270.
A
for the determination of fission product zirconium in plutonium reactor fuel was desired which would be simpler and shorter than the radiochemical methods a t present in l a ) . These methods are rather use (6,6, long and require multiple precipitations from hydrofluoric acid solutions to obtain radiochemically pure zirconium. The time required for such an analysis, and the inconvenience of working with fluoride solutions, led to a search for a noduoride method incorporating a specific reagent for zirconium. Because mandelic acid and its derivatives are specific for quadrivalent ions, this investigation was concerned with applying this selective action to the separation of radiozirconium from other fission products, specifically in irradiated plutonium. Kumins (9) first suggested the use of mandelic acid as a highly selective reagent for the determination of zirconium, Oesper and Klingenberg, in a study of a number of glycolic acid derivatives (1I ) , concluded that p-bromomandelic acid was a superior zirconium precipitant. Hahn (3) reported direct weighing of zirconium p-bromomandelate, which was later applied by Klingenberg and Papucci to the determination of zirconium in steel (8). More recently, Bricker and Waterbury (1) used p-bromomandelic acid to separate microgram amounts of zirconium from milligram amounts of plutonium, after reduction of plutonium(IV) to plutonium(II1) with hydroxylamine hydrochloride. Hahn and Skonieczny (6) applied mandelic acid t o the precipitation of radiozirconium after initial separation of the zirconium from fluoride solution. The radiochemical method developed in the present, investigation is based on METHOD
N. M.
the selective precipitation of zirconium with p-bromomandelic acid, and has the advantage over older methods of being shorter and avoiding the use of fluoride solutions. The large weighing factor produced by the p-bromomandelic acid allows direct weighing and eliminates the necessity of ignition to the oxide. EXPERIMENTAL
Reagents. p-Bromomandelic Acid, 0.1M. Dissolve 2.3 grams of recrystallized p-bromomandelic acid in 100 ml. of hot distilled water. Cool t o room temperature and filter. Zirconium Carrier Solution, 5 mg. of zirconium per ml. Weigh 17.7 grams of reagent grade zirconium oxychloride octahydrate and dissolve and dilute t o 1 liter with 3M hydrochloric acid. Standardize by pipetting 5-ml. aliquots into 150-ml. beakers, adjusting the volume to 25 ml., and increasing the hydrochloric acid concentration to 8 t o 10M. Heat to 80" to 85' C. and add 25 ml. of 0.1M p-bromomandelic acid dropwise with stirring. Digest hot for 15 to 20 minutes, then cool and filter into weighed filtering crucibles. Wash the precipitate with water, ethyl alcohol, and ether. Dry a t 110' C. for 30 minutes and weigh as zirconium tetra-p-bromomandelate. Cerium Carrier Solution, 10 mg. of cerium per ml. Dissolve 15.5 grams of reagent grade cerous nitrate hexahydrate in 500 ml. of 3M hydrochloric acid. Tellurium Carrier Solution, 10 mg. of tellurium per ml. Place 5.0 grams of tellurium metal in a 250-ml. Erlenmeyer flask. Add approximately 10 ml. of 10M nitric acid and heat gently until the tellurium is dissolved. Evaporate to a volume of 3 ml. by swirling over a burner. Add 10 ml. of concentrated hydrochloric acid and evaporate to 3 ml. Repeat the evaporation with concentrated hydrochloric acid two more times. Dissolve residue in 500 ml. of 3M hydrochloric acid. Procedure. Dissolve the irradiated plutonium in concentrated hydrochloric acid. Dilute t o a known volume and a final hydrochloric acid concentration of approximately 6M. T o a suitable aliquot of the irradiated plutonium solution add 1 ml. each of zirconium, cerium, and tellurium carriers. Evaporate just to dryness. Dissolve and transfer the evaporated residue to a 50-ml. centrifuge cone using 16 ml. of 3M hydrochloric acid. Heat the solution in a boiling water
bath, remove from the bath, and saturate with sulfur dioxide gas. Continue bubbling gas through the solution for 1 minute after a precipitate of tellurium metal appears. Return the solution to the water bath for 1 minute, then repeat the addition of sulfur dioxide for about 30 seconds t o allow the tellurium t o agglomerate into large clumps. Centrifuge, and decant the supernatant into a clean 50-ml. centrifuge cone. Add 10 ml. of concentrated hydrochloric acid to the sample and heat in a boiling water bath. Add 10 ml. of the p-bromomandelic acid solution with stirring. Allow the solution to digest hot for 15 minutes. Centrifuge, and remove the supernatant. Dissolve the precipitate in 10 ml. of water containing 6 drops of concentrated ammonium hydroxide. Precipitate zirconium hydroxide from this solution by adding 2 ml. of 12M sodium hydroxide with stirring. Centrifuge and discard the supernatant. Dissolve the zirconium hydroxide by warming with 6 ml. of 8 M hydrochloric acid. Add 1 ml. each of cerium and tellurium carrier. Adjust the volume to 16 ml. with water, and repeat the tellurium, zirconium p-bromomandelate, and zirconium hydroxide precipitations. Dissolve the second zirconium hydroxide precipitate by warming with 15 ml. of concentrated hydrochloric acid and 10 ml. of water, Add 1 ml. of cerium carrier, heat in a boiling water bath, and precipitate zirconium tetrap-bromomandelate as before. Digest the precipitate for 15 minutes in the boiling water bath, then centrifuge, and discard the supernatant. Slurry the precipitate with 10 ml. of 5M hydrochloric acid and filter with suction onto a weighed No. 42 Whatman filter paper, 7/* inch in diameter. Wash with three 5-ml. portions of water, three 5-ml. portions of ethyl alcohol, and finally with three 5 m l . portions of ether. Dry at 110" C. for 15 minutes and weigh as zirconium tetra-p-bromomandelate to determine the chemical yield. Mount the filter circle in a permanent geometry on a n aluminum plate. Count for 6 or y activity in standard counting equipment to determine the Zr95 content. RESULTS AND DISCUSSION
Interferences. Zirconium is t h e only element formed in the fission of plutonium t h a t is precipitated b y pVOL. 32, NO. 12, NOVEMBER 1960
1607
Table 1.
Sample .4 250 B
C ll
Effect of Cerium Holdback Carrier
Original Activity, C.P.M. y,
Zr95
Treatment 2 pptns. ; ‘No Ce present
8 X lo5 a, Am*“ 8 x 10’ a, P U 2 3 9 250 y , Zr96 Same as A 8 x 105 a, ~me41 SameasB 2 pptns. ; Ce present during 1st pptn. Sameas B 2 pptns.; Ce present during both
Final Activity, C.P.M. Alpha Gamma 900,000
980
160,000
19,400
26,000 150
2,400 255
bromomandelic acid. However, cerp-bromomandelate from a low activity tain of the fission elements are carried Zr96 solution to which were added large by the zirconium tetra-p-bromomanamounts of plutonium or americium. delate. These include iodine, rutheAlthough aliquot A was the only sample nium, and tellurium. Interference to which plutonium was added, it shows with counting of the zirconium is rea much smaller y contamination than aliquot B, which contains no plutonium. duced by proper control of the hydrochloric acid concentration during the p This is explained by the fact that the bromomandelic acid precipitations. As plutonium acts as a holdback carrier for the hydrochloric acid concentration is inamericium in aliquot A, thus decreasing creased, the a,mount, of iodine, ruthethe amount of y contamination, alnium, and tellurium carried is decreased. though about 1% of the original plutoHowever, the tellurium interference nium still remains with the zirconium. Aliquots C and D show the reduction in persists, some tellurium being found in the zirconium fraction regardless of conboth a and y contamination when ditions of precipitation. The most s ~ - cerous ion is employed as a holdback cessful technique for eliminating tellucarrier for americium. When americium rium contamination consists of precipiactivity is initially present, it is necestation of tellurium metal prior to the sary to use cerium holdback carrier zirconium precipitations. Two precipduring each zirconium precipitation, to itations of tellurium metal are suffiobtain the correct value of the zirconium activity. cient to remove this activity completely. Since p-bromomandelic acid is not Hydrochloric Acid Concentration. specific for zirconium but rather is Tests were made to determine the selective toward quadrivalent ions, any optimum hydrochloric acid concentraplutonium(1V) would be expected to tion during the zirconium tetra-pprecipitate with the zirconium. The bromomandelic acid precipitation. Ziraddition of sulfur dioxide during the conium precipitations were made tellurium removal also serves to reduce from irradiated plutonium solutions the plutonium to the trivalent state, which were 0.2 to 7 M in hydrochloric which prevents contamination of the acid. The y spectra of some of these zirconium precipitate with plutonium, precipitates are shown in Figure 1. Cerous ion is added prior to each p Zirconium selectivity increases with inbromomandelic acid precipitation as a creasing hydrochloric acid concentraholdback carrier for americium and tion. However, above 5M hydrochloric plutonium(II1). Am*41is an ever-presacid precipitation is very slow, resulting ent impurity in plutonium. Both in estremely long digestion periods to americium and plutonium are a obtain reasonable yields. Below Uf emitters; showing complex a spectra, hydrochloric acid, contamination by along with y transitions associated wit’h tellurium, ruthenium, and iodine activthose a transitions which go to excited ities increases rapidly. Zirconium prestates of the daughter nuclides. A high cipitates formed from hydrochloric acid percentage of the americium a’s occur solution of less than 3M concentration with a 60-k.e.v. y-ray, while only a few are quite fine and tend to be washed of the plutonium a’s are associated with through the filter paper. The work of y-rays of sufficient energy to be detwted Hahn and Baginski (4) indicates that with ordinary &,intillation counters (2). precipitates of zirconium obtained from For this reason, contamination of the solutions containing less than 5 M final precipitate with americium is much hydrochloric acid were contaminated more serious than with plutonium. with zirconium oxymandelates. To enTable I illustrates the magnitude of sure formation of the tetramandelate, americium interference with the y they found the solution should be 5M counting of zirconium, and the effecin hydrochloric acid. Because the final tiveness of cerium holdback carrier in precipitate is to be weighed for the yield reducing this interference. The data in determination, a stoichiometric comthis table were obtained by making pound must be formed. For these double precipitations of zirconium tetrareasons, the optimum hydrochloric acid 1608
ANALYTICAL CHEMISTRY
02
0 4
06
0.8
GAMMA E N E R G Y ( M E V )
Figure 1 . y-Ray spectra of zirconium tetra-p-brornornandelate precipitated from different hydrochloric acid concentrations Precipitate formed in: Top. 0.2M acid Middle. 2M acid Bottom. 5 M acid
concentration after addition of all reagents should be 4 to 5 M . Niobium Contamination. Nb96 is the daughter of ZrQ5, and decays b y p emission t o &IoQ5. The fl radiations of this isotope are quite weak and the y energy associated with the decay of this isotope is indistinguishable from the Zrg5y activity. Thus it is virtually impossible to detect small amounts of Nb95 in mistures of this activity with Zrg5. To find out if niobium is occluded with the zirconium tetra-p-bromomandelate, a zirconium separation was made by the proposed method. The final zirconium tetra-p-bromomandelate precipitate was dissolved in dilute ammonium hydroxide, and zirconium hydroxide w&s precipitated and washed free of p -
bromomandelic acid. The zirconium hydroxide was then dissolved in dilute acid, niobium carrier was added, and a chemical separation of the niobium was made by the method of Morris and Scargill (10). The y activity of the separated niobium was 200 counts per minute (c.p.m.), compared to the original zirconium activity of 71,000 c.p.m. This corresponds to a maximum niobium contamination in the separated zirconium of less than 0.3%. Approximately one third of this amount can be accounted for as niobium growth between the final zirconium precipitation and the first niobium separation. Isotopic Exchange. Early workers in the field of fission product analysis were plagued by incomplete isotopic exchange between carrier and radiozirconium. This was attributed t o formation of zirconium radiocolloids in the nitric acid solutions of irradiated uranium. Hume (6) showed that complete interchange between carrier and radiozirconium could be achieved by the addition of fluoride to these solutions prior to chemical treatment, but it was not certain that fluoride ion was essential to obtaining complete isotopic exchange in all types of solutions. T o find out whether or not complete isotopic exchange is achieved by the proposed method, tn o separate plutonium fuel samples were analyzed for Zr95, both by this method and by a standard fluoride method (1.9). In the first plutonium source, which contained only a small amount of Zrg5, the p-bromomandelic acid method gave Zr95 y specific activities of 178 c.p.m. per ml. of sample, while the fluoride method zirconium samples gave 172 c.p.m. The second plutonium source, which had received a longer irradiation, was found to contain 71,800 Zrg2y c.p.ni. per ml. of sample by the p-bromomandelic acid method, and 71,000 c.p.m. by the fluoride method. Zr95 fi specific activities for this source were 539,000 disintegrations per minute (d.p.m.) by the p bromomandelic acid method and 542,000 d.p.m by the fluoride method. The observed count rates obtained by both methods agreed within the experimental error of the methods. Thus for the plutonium-hydiochloric acid systems involved in this discussion, complete isotopic exchange brtween radiozirconium and added carrier is achieved without the addition of hydrofluoric acid. Purification of p-Bromomandelic Acid. Separations of Zr95, made during the initial phases of this study, sometimes showed contamination with and Ru'03. The extent of contamination was not consistent, as varying amounts were found under identical chemical conditions. Multiple precipitations of zirconium p-bromomandelate failed to reduce the amount of contami-
Table II. No. of
4
Effect of p-Bromomandelic Acid Purity
Total y C.P.M. from Ppt." Purified Reagent, MI. Unpurified Reagent, M1.
Pptns.
10
15
10
15
1 2 3 4
106,000 103,000 105,000 104,000
112,000 108,000 114,000 117,000
111,000 103,000 103,000 103,000
120,000 101,000 103,000 103 ,000
Fission solution contained 103,000
for yield of carrier zirconium.
y
c.p.m. of
nation by these isotopes. This led to the suspicion that the commercial grade pbromomandelic acid might contain impurities which would tend to precipitate these easily reduced anions. Accordingly a 50-gram batch of the commercial p-bromomandelic acid was recrystallized from benzene as described by Klingenberg (7'). The melting point of the recrystallized product was 116' to 117' C., as compared to the original melting point of 114' to 115' C., indicating substantial purification. Tests were made using both the purified and unpurified reagent for the analysis of an irradiated plutonium sample containing 103,000 Zrg5y c.p.m. per ml. of solution. Precipitations were made using 10- and 15-ml. portions of 0.1M p-bromomandelic acid reagent to precipitate zirconium from 5M hydrochloric acid solution in the presence of cerous holdback carrier. The y count data are shown in Table 11. When the unpurified reagent was used, the amount of contamination wm erratic, and did not decrease with multiple precipitations. Using an excess of the unpurified reagent, more contamination was observed after multiple precipitations than after a single precipitation. By contrast, the results obtained using the purified reagent showed that practically all of the contamination was removed with two precipitations of zirconium tetra-p-bromomandelate, and that an increase in the amount of reagent used did not result in increased contamination. It is strongly recommended that the p-bromomandelic acid be purified prior to use. Some batches of the reagent have been satisfactory as received, but the precaution of routinely recrystallizing the reagent will eliminate contamination by iodine and ruthenium. General Remarks. A single determination b y this method requires about 3 hours, and four determinations may be made simultaneously in about 4 t o 5 hours. Chemical yields are about 75%. Decontamination from plutonium is excellent, with only 10 to 20 Q c.p.m. remaining on the precipitate, from an original 8 X lo7 c.p.m. for aliquots containing 1 mg. of plutonium. Beta absorption curves, decay curves, and y pulse height meas-
Zr95.
All count rates were corrected
Table 111. Typical Yields and Precisions Zr95,
y
Ali- % C.P.M.1 Sample quot Yield .MI. Average 1
30
40
4
75.6 75.8 76.7 77.2
1 2 3
85.8 69,700 84.8 69,500 81.7 67,400
1
60.5 62.6 59.4
1 2 3
2 3
82,200 82,500 87,800 82,500
71,600 72,200 71,600
83,750 f 1400
68,870 f 800 71,800 f 230
4 The similar count rates of Samples 3 and 4 are coincidental. These are different sampies.
urements show no detectable fl or y emitting contaminants. Table 111gives typical yields and precisions which can be expected from this method for the analysis of Zrg5 in neutron irradiated plutonium. The precision shown with each average is the standard deviation, calculated from the range for that average (IS). By taking the analyses from all four samples and eliminating the between samples variance, a standard deviation for a single determination of 1670 c.p.m. is obtained, which corresponds to a 2.3 yo standard deviation for a single determination. The method may be applied equally well to the determination of 17-hour Zrg7. No interference from short-lived fission products has been detected when zirconium samples have been run a few hours after the plutonium irradiation. ACKNOWLEDGMENT
It is a pleasure to acknowledge the helpful advice of Clark E. Bricker and the aid of Gilbert B. Nelson, who performed some of the analyses. The conVOL. 32, NO. 12, NOVEMBER 1960
1609
tinuing interest and support of C. F. Metz are gratefully appreciated. LITERATURE CITED
(1) Bricker, C. E., Waterbury, G. R. ANAL.CHEM.29, 558 (1957). ( 2 ) BuLermak, J., Lew, M., Matlack, G., lbid., 30, 1759 (1958). (3) Hahn, R. B., Ibid., 23, 1259 (1951). (4) Hahn, R. B., Baginski, E. S., Anal. Chim.Acta 14, 45 (1956). (5) Hahn, R. B., Skonieczny, R. F.,
A’ucleonics 14, No. 4, 56 (19%). (6) Hume, D. N., “Radiochemical Studies: The Fission Products,” C. D. Coryell and N. Sugarman, eds., National Xuclear Energy Series, Div. IV, Vol. 9, p. 1499, McGraw-Hill, New lg51. (7) Klingenberg, J. J., “Organic Syntheses,” T. L. Cairns, ed., Vol. 35, p. 11, Wiley, New York, 1955. (8) Klingenberg, J. J.1 PaPucci, R. A., ANAL.CHEM.24, 1861 (1952). (9) Kumins, c. A., Ibid., 19, 376 (1947). (10) hforris, D. F. C., Scargill, D., Anal.
Cham. Acia 14, 57-61 (1956). (11) Oesper, R. E., Klingenberg, J. J., ANAL.CHEM.21, 1509 (1949). (12) Stanley, C. W., Ford, G. P., Lang, E. J., U. S. Atomic Energy Commission Rept. LA-1721 (Rev.), J. Kleinberg, ed.,
December 1956, unclassified. (13) Youden, W,. J., “Statistical Methods for Chemists, p. 12, Wiley, New York, 1951. RECEIVED for review June 6, 1960. Accepted July 18, 1960. Work done under the auspices of the Atomic Energy Commlsslon.
Determination of Oxygen in Zirconium and ZircaIoy by the Inert Gas Fusion Method Pi- INEAS ELBLING and G. W. GOWARD Bettis Atomic Power laboratory, Westinghouse Electric C o p , Pittsburgh, Pa. ,The important effects of oxygen content on the physical properties of zirconium and Zircaloy necessitated a rapid and accurate method for determining oxygen in these metals. The inert gas fusion method has been found satisfactory for this determination. Oxygen is released from the metal as carbon monoxide by reaction with carbon in the presence of molten platinum in an induction-heated graphite crucible. The carbon monoxide is swept from the reaction furnace with argon, oxidized to carbon dioxide, and determined conductometrically. A minimum weight ratio of platinum to sample of 7 to 1 is necessary for complete removal of oxygen from samples. The coefficient of variation at the of the method is about +6% 1000-p.p.m. level of oxygen. Analysis of samples containing known amounts of oxygen in the range of 900 to 3700 p.p.rn. has shown that the method is quantitative within the limits of precision.
widespread use among producers and users of zirconium. Codell and Norwitz (a) have applied the bromination method to the determination of oxygen in zirconium. This procedure involves the reaction of the metal and its contained oxygen with bromine and carbon a t 825” C. in the .presence of an inert carrier gas to produce carbon monoxide. The carbon monoxide is swept from the reaction tube, oxidized to carbon dioxide, absorbed on Ascarite, and weighed or determined conductometrically (3). The inert gas fusion technique was
first described by Singer (7) and later improved by Smiley (9). The method is analogous to vacuum fusion with the vacuum replaced by an inert sweep gas, thus eliminating the difficulties associated with the production and maintenance of high vacuum. As in the vacuum fusion method, carbon reacts with the oxygen in the sample to form carbon monoxide, usually in the presence of a molten metal, such as platinum (9), as the reaction medium. The resulting carbon monoxide is swept from the furnace tube and oxidized to carbon dioxide by means of heated copper oxide (7) or iodine pentoxide
S
EVERAL ?~IETHODS have been used,
with varying degrees of success, for the analysis of zirconium for oxygen content. The hydrogen chloride method, as developed by Read and Zopatti (6), has been used until recently in this laboratory for acceptance and engineering testing. The adaptation of vacuum fusion techniques for the analysis of oxygen in zirconium has been reported by several authors (6, IO). Sloman and Harvey (8) discussed the fundamental reactions in the vacuum fusion method and described its application t o the determination of oxygen in zirconium. Because of the delicate and expensive nature of the apparatus required and the need for highly skilled operators, the vacuum fusion method has not found
1610
ANALYTICAL CHEMISTRY
TO L E C O CONDUCTOMETRIC UNIT
Figure 1 . 1.
Inert gas fusion apparatus
Two-stage regulator Third stage regulator 3. Purifying train A. Sulfuric acid tower 8. Ascarite and magnesium perchlorate C. Flowmeter A. Needle valve 5. Neoprene tubing 6. Argon purification tube A. Nickel tube 8. Glars wool C. Zirconium chips D. Split-tube furnace, 700’ to 800’ C.
2.
7. 8. 9. 10. 11. 12. 13. 14.
Hose clamp Vycor furnace tube Radiofrequency coil Crucible thimble assembly Cooling blowers Sample storage arm Sample loading port Oxidizer furnace A. Iodine pentoxide 8. Glass wool C. Electrical heating t a p e D. Sodium thiosulfate
