within a few hours of separation. The strontium-90 can then be determined by separating the yttrium-90 by cation exchange after allowing the daughter to grow into equilibrium. Barium. T h e barium fraction is eluted with 2.0M isobutyrate, p H 6.20, and will contain some lanthanum-I40 which has grown in during the elution. The activity is determined directly in t h e well counter. A correction must be made for the daughter growth from the end of the strontium separation to the counting time. This is usually a n hour or less and will require up to a 5% activity correction in the scintillation counter. A correction curve for the growth of the lanthanum-140 daughter was obtained from a sample of pure barium-140 which was separated by repeated precipitations of lanthanum hydroxide with ammonium hydroxide. RESULTS AND DISCUSSION
Table I1 gives the barium and strontium activities obtained from two uranium fission mixtures, A and B, 2 and 80 days after bombardment in the Materials Testing Reactor a t Arco, Idaho. The number of fissions based on molybdenum-99 was determined for each sample by the standard radiochemical carrier procedure and by the
ion exchange noncarrier method. Aliquots were then analyzed for the alkaline earths by the procedure given in column 2. For sample A it was possible to determine strontium-91 in the first two aliquots, which gave lo5 gamma counts per minute 3 days after bombardment time. Also, where no 0.1N hydrochloric acid anion exchange separation was included for the younger sample, the barium fractions contained 5 to 10% contamination, mostly the 34-hour rhodium-105. This was removed by recycling through a second cation column. The lower limit for accurate strontium-89 bremsstrahlung measurement in the 3inch gamma well scintillation counter with a background of 400 c.p.m. was 10” fissions or 800 c.p.m. It should be possible to lower this limit with low background counters. One could reduce the number of fissions required for a satisfactory strontium analysis by 8-ray counting techniques, but these are more exacting and time-consuming. Since the alkali metals and rare earths are adsorbed on the cation column together with the alkaline earths, investigations are now being carried out to develop methods for their quantitative determination. Preliminary results indicate that the alkali metals, sodium and cesium, can be eluted individually before the rare
earths. The latter can then be separated as a group with little or no other fission product contamination. A quantitative carrier-free method for the analysis of the individual rare earths is also being investigated. I n addition, the silver and cadmium radionuclides are quantitatively adsorbed on the 0.1N hydrochloric acid anion column with the rhodium, and conditions are now being sought for their selective elution. LITERATURE CITED
(1) Baerg, A. P., Bartholomew, R. M., Can. J. Chem. 35,980 (1957). (2) Berman, S. S., McBryde, W. A. E., Ibid., 36,835 (1958). (3) Delucchi, A. A., U. S. Naval Radio-
lonical Defense Laboratorv. San Franciko, unpublished data, 1%8. (4) Glendenin, L. E., Paper 260, “Radiochemical Studies. The Fission Products,” by C. D. Coryell and N. Sugarman, D. 1549. McGraw-Hill, New
York, f951. ‘ (5) Smith, H. L., Hoffman, D. C., J. Inorg. and Nuclear Chem. 3, 243 (1956). (6) Tompkins, P. C., Wish, L., Burnett, W. T., Jr., ANAL. CHEW 22, 672 (1950). (7) Wish, Leon, Ibid., 31, 326 (1959). (8) Wish, Leon, U. S. Naval Radiological
Defense Lab. ReDt. USNRDL-TR-312 (March 1959).
RECEIVEDfor review May 17, 1960. Accepted August 22, 1960.
Determination of Uranium in Zirconium Ores A Modification of the Stannous Chloride Method K. BRlL and S. HOLZER Research laboratory, Orquima Sf A , Sao Paulo, Brazil
b The stannous chloride method, proposed by Main for uranium determination, yields erratic results in the presence of large amounts of zirconium, probably because of coprecipitation of uranium with zirconium phosphate. The interference of zirconium disappears when sodium fluoride is used instead of orthophosphoric acid to obtain a complete reduction of uranium (VI) to uranium(lV) by means of stannous chloride. The modified stannous chloride reduction method is applied for the analysis of uraniferous zirconium ores containing 0.05 to 1% of &OS. Extraction with tributyl phosphate eliminates interfering elements. Uranium is finally determined by titration with ceric sulfate solution, using ferrous o-phenanthroline as end point indicator.
V
have been proposed for the volumetric determination of uranium based on the reduction of uranium(V1) to uranium(1V) by means of solid or liquid reductors. Liquid reductors offer the advantage of simpler manipulation and better reproducibility, especially when small amounts of uranium (milligram range of USOS)are to be determined. Reduction of uranium by means of stannous chloride in the presence of iron and orthophosphoric acid as “catalysts,” proposed by Main ( l a ) , allows both high precision and reproducibility in the volumetric determination of uranium, as was shown recently by Byme, Larsen, and Pflug ( 2 ) . Several elements interfere in this reduction method. Copper, iron, chromium, vanadium, titanium, and molybdenum give high results (2, ARIOUS METHODS
12). Erratic results were reported if perchloric acid was present during the reduction step (2). Main’s method fails if large amounts of zirconium are present during the reduction step. Byme, Larsen, and H u g (2) state that in the presence of zirconium, uranium is coprecipitated with zirconium phosphate, giving somewhat low results. I n the concentration range studied (up to 2% zirconium in uranium) the error introduced by the presence of zirconium was rather small (up to 0.15%). However, the results obtained with increasing proportions of zirconium to uranium are completely erratic. I n a n effort to eliminate the interference of zirconium we searched for catalysts, other than orthophosphoric acid, for the stannous chloride reducVOL 33, NO. 1, JANUARY 1961
55
tion of uranium(V1). K e found t h a t uranium(V1) is completely reduced to uranium(1V) by stannous chloride in the presence of iron and fluoride ions. The replacing of orthophosphate by fluoride ions completely eliminates the interference of zirconium in the uranium determination, at least up to a 40-fold excess of Zr over u308 I n the absence of phosphate ions, the titration with potassium dichromate using diphenylamine as indicator, as proposed by Main (12), does not yield sharp end points. The substitution of fluoride for orthophosphate thus makes it necessary to introduce some further, but minor, modifications in the original Main method. I n particular, sharp end points can be obtained by using ceric sulfate as titrant and ferrous o-phenanthroline as end point indicator. The stannous chloride reduction of uranium in the presence of fluoride ions was applied for the quantitative determination of uranium in uraniferous zirconium ores occurring in Pocos de Caldas, State of Minas Gerais, Brazil. The elaborated procedure involves as a preliminary step the separation of uranium by tributyl phosphate (TBP) extraction. T B P extraction from nitric acid solutions effectively separates uranium (1, 3-8, 10, I S , 14) from most of the elements that interfere in the determination of uranium by means of the modified stannous chloride reduction. However, in thP milligram range of C.08 i t was rather difficult to get rid completely of some commonly occurring elements, probably introduced during the manipulations following the T B P extraction of uranium. Of those elements, only iron interferes in the volumetric determination of uranium. Its interference is stoichiometric. A spectrophotometric* correction for the amount of iron accidentally introduced was necessary in order t o determine uranium with a precision to 1% down to the range of some tenths of I 70of U308 in zirconium minerals.
Ferric chloride solution. 0.00200Ar.
6N in HC1. Hydroxylamine hydrochloride solution. 100 prams Der liter. Sodium-acetatk, 2 M . o-Phenanthroline hydrochloride, 0.1% solution. T B P (technical grade) mixture with heptane (technical grade), 50 volume % of TBP. Wash solution, 2.5M NaN03 and
1.O-U"03. Reagent grade chemicals were used throughout this work. Reduction and Titration of Uranium. The sample of uranium to be analyzed should be in t h e form of a sulfate or chloride solution. D r y t h e sample, and take u p t h e d r y residue with 2 ml. of concentrated HC1. Add 1 nil. of sodium fluoride solution and exactly 1 ml. of 0.002N ferric chloride solution. Heat just to boiling and add 1.5 ml. of stannous chloride solution. Cover the beaker with a watch glass and leave i t for 5 minutes on a boiling water bath. Add 0.5 ml. of stannous chloride solution and keep the beaker for 5 minutes more on the water bath. Repeat this operation once more. Cool d o w the reduced uranium solution in a COS atmosphere. Using 2 ml. of (1 to 10) wash down the watch glass and the beaker walls. Add 2 ml. of the saturated solution of mercuric chloride. Let the precipitated HgZCl2age for 2 minutes. Add 1 ml. of the 8% solution of ferric sulfate, maintaining the solution in a slow motion. Filter through a small glass filter funnel of medium porosity while passing a slow current of COz over the funnel. Wash the beaker and the funnel with deaerated H2S04 (1 to lo), until the volume of the filtrate and TTashings together is 40 to 50 ml. If no precipitate of Hg2Cl2 forms after addition of HgC12, repeat the reduction, using a greater escess of stannous chloride. If for some reason the reduced solu-
Table I. Accuracy and Reproducibility of Volumetric Determination of Uranium
EXPERIMENTAL
Reagents. Cerium sulfate solution, 0.01000N (9). Mohr's salt solution, 0.01000N. Uranyl sulfate solution, 5.086 mg. of U308per ml. (standardized gravimetrically). Stannous chloride solution, 1 gram of SnC12.2HzO per 100 ml. of 1N HC1 (prepared daily). Sodium fluoride, solution, 40 grams of N a F per liter. Mercuric chloride, saturated solution. Ferric sulfate solution, 80 grams of Fe2(S04)3.7H~0and 100 ml. of HzS04 (1 t o 1) per liter. Sodium carbonate solution, 0.2 gram of NaZC03 per liter. Ferrous o-phenanthroline solution, 2.5 X lO-3M (in Fe+z).
56
ANALYTICAL CHEMISTRY
UBOa Taken, Mg.
Ce-
(SO1)2, MLa
U308 Found,
%
Mg.
0.74 0.73
1.025 1.01
100.8 99.3
2.543
1.83 1.83
2.54 2.54
99.9 99.9
5 086
3.66 3.67 3.66
5.085 5.10 5.08 5.07 5.10
100.0 100.3 99.9 99.7 100.3
3.67 10.17
7.33 7.30
10.17 10.13
100.0 99.6
0.009881X Ce(SO& solution used; 0.23-ml. reagent blank subtracted from titer found to obtain uranium titer Q
According to the literature, 0.liV ceric sulfate solutions can be used for direct titration of ferrous iron solution in the presence of mercurous chloride; the oxidation of Hg2C12 by means of ceric sulfate is slow a t room temperature (9). We found, lion-ever, when n-orking with dilute solutions of ferrous iron, that consumption of ceric sulfate by Hg*ClZ is bv no means negligible; therefore HgZCl2must be filtered off before the titration can be performed. Reagent Blank. The reagent blank is due mainly t o the consumption of ceric sulfate by t h e iron catalyst and indicator solutions. Trace amounts of iron can be introduced also during t h e reduction of uranium. The reagent blank was made daily and found t o be equivalent to 0.23 =t 0.005 mi. of the 0.01N ceric sulfate solution; maximum deviation nas within 0.01 ml. The reproducibility of the blank depends upon the maintenance of acidity conditions during the precipitation of mercurous chloride, High blanks were found if the precipitation of Hg2CIz OCcurred at acidities appreciably higher than indicated in the reduction-titration procedure.
Theo-
retical Titer
1.017
3.65
tion of uranium cannot be titrated a t once, leave it in a carbon dioxide atmosphere. Under such conditions solutions of uranium(1V) were found to be perfectly stable; even after 6 hours' standing, no measurable reoxidation of uranium(1V) took place. Add to the filtered solution 0.10 ml. of the ferrous o-phenanthroline solution. Titrate with standard 0.01-V c,eric sulfate solution using a 5-ml. microburet graduated in 0.01 ml. The tip of the microburet must dip into the solution to be titrated. At the end point a sharp color change from red to greenish yellow occurs. During the titration maintain the solution under good agitation. If the solution waa overtitrated, proceed to a back-titration with the solution of JIohr's salt. Calculate the uranium content of the sample taking into account the reagent blank (see below).
EXPERIMENTAL RESULTS
Accuracy and Reproducibility of Titration Method. Table I shows t h e reproducibility of uranium determination attained in pure solutions. Table I1 shows that the efficiency of the uranium reduction with stannous chloride and the accuracy of the titration with ceric sulfate are not affected within rather large limits by the concentration of either sodium fluoride or ferric chloride. Table 111 shows the protecting effect of a carbon dioxide atmosphere upon the stability of reduced uranium solutions, I n the absence of C02results are
not reproducible Stannous chloride is rapidly oxidized if the solutions are exposed to air. The stability of uranium(1V) solutions exposed to air is erratic. Some solutions remained completely reduced even after the air oxidation of the excess stannous chloride. Others, reduced under apparently identica! conditions. reoxidizd rather rapidly. I n the presence of COS the reoxidation of uranium was not noticeable. Effect of Zirconium on Determination of Uranium. Table I V shows t h a t whereas t h e original method of RIain can be scaled d o n n t o t h e milligrani range of UaOe, the presence of zirconium badly affects the accuracy of the uranium determination Diffuse end points are obtained nith increasing proportion of zirconium to uranium. The accuracy of uranium determination is not affected if the determination is made according to our procedure, even in the presence of a 40-fold cxccsq of zirconium. DETERMINATION OF URANIUM IN ZIRCONIUM ORES (CALDASITE TYPE)
A typical sample of caldasite contains ZrOn 56.2%; SiOZ21.2%; Fe20316.7%; &OS 2 3%; TiOt 0.5%; MnOz 0.5%; ant1 USOS 0.32%. Uranium is ssociated so closely with zirconium that quantitative recovery of uranium requires coniplete solution of the mineral ( 1 1 , 16).
Solution of Mineral. Grind t h e ore to pas? 250-mesh. TS'eigh out 2 grams of a representative sample. Introduce 5 grams of sodium hydroxide prllets in a nickel crucible. Transfer t h e weighed sample of t h e ore t o t h e crucible and cover with 5 grams of S a O H pellets. Cover t h e cluvible and heat s l o ~ l yuntil t h e mash begins to melt. Place t h e crucible in a furnace at 900" C. After about 20 niinutes, take out the crucible and let it cool down. Transfer the melt from the crucible into a 400-ml. beaker, using about 100 ml. of water. Add 40 ml. of concentrated nitric acid and a few drops of hydrogen peroxide, and evaporate the solution to dryness on a water bath. Leave the beaker for one hour in a drying oven a t 110' C. to ensure complete dehydration of silica. Add 80 ml. of 1~44nitric acid, heat the solution just to boiling, and filter through S. & S. black ribbon filter paper. Wash the residue from the beaker, using four 5-nil. portions of 1;M nitric acid. Keep the filtrate together with the washings (solution X). Transfer the silica residue from the filter funnel into a platinum dish, using a fine water jet. Add concentrated HF dropwise until the precipitate dissolves. Evaporate to dryness on a sand bath. Take u p the residue with a few milliliters of 1M HKo, and join i t (without filtration) with solution X. Evaporate to about 80 ml. and transfer the solution
to a 250-ml. separatory funnel aashing out the beaker with distilled water to bring the volume of the solution in the funnel to about 100 ml. (solution A). Solution A prepared according to the described procedure is 2.5M in sodium nitrate and 1M in nitric acid. Extraction of Uranium with TBPHeptane Mixture. Shake vigorously, for a t least I minute, solution A contained in t h e 250-ml. separatory funnel n i t h 100 ml. of t h e T B P heptane mixture. Allow t h e layers to separate. Transfer t h e aqueous phase t o another 250-ml. separatory funnel and t h e organic phase to a 500-ml. funnel. Repeat the extraction of thc water phase, again using 100 ml. of the T B P mixture. Join both organic extracts in the 500-ml. separatory funnel (solution B). Discard the aqueous phase (solution 1). Wash organic extract B with five successive 20-ml. portions of the wash solution. Join the aqueous washings in a 250-ml. separatory funnel and extract them with a n equal volume (100 ml ) of the T B P mixture (solution C). Discard the aqueous phase (solution 2). Wash organic phase C with three consecutive 10-ml. portions of the wash solution, each time discarding the aqueous layer (solution 3 ) . Add washed organic phase C to main extract, 13, thus making a tot 21 of about 300 nil. of the TBP-heptane uraniumcontaining mixture (solution D), Strip uranium from solution D using successive. 50-ml. portions of distilled water until the aqueous extract is only slightly acid to Congo paper and then three successive 50-ml. portions of a sodium carbonate solution containing 0.2 gram per liter of NaZC03. Discard the organic phase (solution 4). Join all nater estracts in one separatory funnel and wash them with 50 ml. of heptane t o eliminate any disso1vc.d T R P (solution E). Evaporate aqueous phase E to a volume of about 25 ml. Add 0.5 ml. of perchloric acid and evaporate until the fumes of HC10, disappear. Repeat the evaporation step to complete the destruction of any organic matter. Add 0.5 ml. of concentratd HzS04 and evaporate again until fumes of sulfuric acid disappear. Repeat this operation once more, using 0.5 ml. of HzS04 to eliminate perchlorate ions completely. Take up the residue with a few drops of Hi304 and add water to bring the volume to 25 ml. in a volumetric flask (solution F). Transfer 1 ml. of solution F into another 25-ml. volumetric flask for iron determination. Transfer 20 ri1. of solution F into a 50-ml. beakcr and evaporate it to dryness on a water bath for uranium determination (see "reduction and titration of uranium"). Iron Correction. T h e amoLnt of iron in t h e washed T B P extract is insignificant. However, u n d e - t h e conditions of routine work i ; was rather difficult t o prevent small amounts of iron (10 to 50 pg.) from contaminating our solutions during the
Table II. Effect of Ferric Chloride and Sodium Fluoride Concentrations on Reduction of Uranium with Stannous Chloride
0.002 % N TheoFeC13, usoh Mg. retical M1. Taken Founda Titer 5.086 4.06 79.8 d.'lO 5.086 5 10 100.3 0.10 5.086 5.11 100.5 0.50 5.086 5.09 100.1 0.50 5.086 5.09 100.1 1.00 5.086 5.09 100.1 1.00 5.086 5.10 100.3 . . . 1.00 5.086 4.59 90.3 ... 1.00 5.086 4.75 93.4 0.10 1.00 5.086 5.08 99.9 0.25 1.00 5.086 5.07 99.7 1.00 5.086 5.07 99.7 0.50 1.00 10.17- 10.17 100.0 1.00 1.00 5.086 5.09 100.1 1.00 10.17 10.13 99.6 a Value of blank determined for every concentration of FeC13.
NaF (40G./ L.), M1. 1.00
Table 111.
Stability of Uranium(lV) Solutions (5.086 mg. of Us08 taken)
Samples Exposed to Time Elapsed Air COz between Reduction and Titration of UIV us08 Found, Mg. 20 to 30 min. 5 09 5.09 1 to 1.5 hours 5.09 5.10 5.02" 5.10 5.07" 5.09 3 to 3 . 5 hours 4 97" 5 09 7 to 8 hours 4 86" 5 09 5.03" 5.07 a After addition of HgZC1, solution remained limpid, indicating complete oxidation of stannoue chloride. Table
IV.
Volumetric
Determination
of Uranium in Presence of Zirconium Reduction in Presence-~ of __ Phos-
Zr Taken, Mg.
UaOe Taken, Mg.
phoric Sodium acid fluoride UiOe Found, -..M ..g-.
5.086 4.69" 5.086 4.76a 5.086 4.87a 5.086 4.72a 5.086 4.25" 200 5.086 3.40" 200 5.086 3.W End point not sharp. 10
20 20 40 100
5.08 5 08
5.06
5 06 5.08
rather lengthy manipulations which follow the T B P extraction of uranium. To 1 ml. of solution F add 1 ml. of hydroxylamine, 5 ml. of sodium acetate solution, and 1 ml. of o-phenanthroline. Bring the volume to 25 ml. with water. VOL. 33, NO. 1, JANUARY 1961
57
After 5 minutes measure the absorption of this solution at 5150 A. against a reagent blank. Calculate the iron content from a standard calibration curve. Uranium Recovery by Proposed Analytical Procedure. T h e recovery of uranium was tested by determining uranium in all solutions discarded in the recommended procedure. Uranium loss due to incomplete extraction was determined by repeating the Table V. Reproducibility of Duplicate Determinations of U308 in Caldasite (Over-all recovery of uranium.
5.086 mg. of UsOs added)
Sample 1 2 3 4 5 10 25-36
Us01
%"
0.336 0.339 0.317 0.314 0.307 0.304 0.307 0.306 0.045 0.046 0.248 0.246 0.369 0.370
US08 Found, Mg." 5.12
%Recovery 100.7
5.11 5.08 5.10
100.5 99.9 100.3
5.12
100.7
5.06
99.5
5.16
101.5
5.13
100.9
Reagent blank and iron correction both taken into account.
extraction of uranium from solution 1 and found to be less than 1%. Uranium loss due to washing of the organic extract was determined by re-extracting uranium from solution 2. Uranium remaining in the organic extract after sodium carbonate stripping (solution 4) was determined by repeating the alkaline washing. Uranium was fmally determined polarographically. The amount of uranium found in solutions 2 and 4 was below 0.1%. An important loss of uranium would result on omitting the fluorization step. A significant adsorption of uranium on silica was found. Thus analyzing a sample of caldasite containing 0.35% of UIOs we found that 0.11 mg. of UaOs was adsorbed on silica, which corresponds to 1.5% of the uranium content. I n Table V the reproducibility of the proposed method for uranium determination is illustrated by typical results of duplicate analysis (column 2) of some caldasite samples. The aqueous phase (solution 1) after the T B P extraction contains most of the original constituents of the analyzed ore. A known amount of uranium was added to this solution (see Table V) and thereafter determined according to the outlined procedure. Table V shows the over-all recovery of the added uranium (column 4), which constitutes a good measure of the accuracy attainable by the analytical process under discussion.
LITERATURE CITED
(1) Bril, K., et al., "Manual of Analytical Methods for the Control of Chemical Processing of Uranium and Thorium," Research Laboratory, Orquima S/A, Sao Paulo, Brazil, LPO-2 (1959). (2) Byme, J. T., Larsen, M. K., Pflug, J. L., ANAL.CHEM.31,942 (1959). (3) Clinch, J., Gray, M. J., Analyst 82,800 (1957). (4) Eberle, A. R., Lerner, M. W., ANAL. CHEM.29,1134 (1957). (5) Fisher, D. J., Thomason, P. F., Ibid., 28,1285 (1956). (6) Franpois, C. A., Ibid., 30,50 (1958). (7) Guest, R. J., Can. Dept. Mines Tech.
Surveys, Mines Branch, Radioactivity Div., Topical Rept. TR-128/55(1955). (8) Kiba, Toshiyuki, Bunseki Kagaku
6, 597 (1957). (9) Kqfthoff, I. M., "Volumetric Analysis, Vol. 11, p. 491, Wiley, New York, 1929. (10) Lerner, M. W., NBL-103, 89 (1955). (11) Maffei, F. J., Pucci, J. R., Ferreirra,
W., Proceedings International Conference on Peaceful Uses of Atomic Energy, Vol. 8, p. 116, 1955. (12) Main, A. R., ANAL.CHBM.26, 1507 (1954). (13) Peppard, D. F., Gurgel, M. V., C. P. At. Enerev Comm.. ANL-4490. 64 (1950). (14) Peppard, D. F., Mason, G. IT., Gurgel, M. V., J. Inorg. Nuclear Chem. 3,370 (1957). (15) Santini, P., Diehl, F., Anais msoc. brasil. quim. 11,167 (1952). RECEIVEDfor review February 2, 1960. Accepted September 8, 1960. Based on work performed under contract for the Brazilian Atomic Energy Commission (Comissao Nacional de Energia Nuclear), whose support is gratefully acknowledged. -I
Differential Thermal Ana lysis and T hermogravimetric Analysis of Fission Product Oxides and Nitrates to 1500' C. P. F. CAMPBELL, M. H. ORTNER, and C. J. ANDERSON' Vitro laborafories, Division of Vifro Corp. o f America, West Orange,
b Apparatus is described for differential thermal analysis (DTA) and thermogravimetric analysis (TGA) in air to 1500' C. This equipment was used to study the thermal stability of strontium oxide, strontium nitrate, cesium nitrate, zirconyl nitrate dihydrate, cerous nitrate hexahydrate, ruthenium dioxide, and mixtures of these materials with alumina. Evidence is presented for the formation of CsA102 in the temperature range 940' to 1100" C., and the course of the thermal decomposition of RuOZ is described. 1 Present address, Crose-Malaker Laboratories, Mountainside, N. J.
58
ANALYTICAL CHEMISTRY
T
N. J .
of radioactive liquid wastes, resulting from the reprocessing of spent fuel elements, into a granular solid by a fluidized bed calcination process is under investigation by the Atomic Energy Commission ( 7 ) . The product of this operation is a solid mixture of aluminum oxide and small amounts of radioactive fission product oxides and nitrates. The calcined material is then stored in underground, air-cooled vessels. Of concern in this processing scheme is the possibility of failure of the cooling system, resulting in a subsequent temperature rise to 1500" to 2000" C. Under these conditions the radioactive solids, which are normally stable at lower temperatures, might decompose HE CONYERSION
or volatilize and escape to the surrounding area by rupturing the storage vessel. This work was undertaken to investigate the seriousness of the problem by determining the thermal stability of selected fission product oxides and nitrates a t temperatures to 1500" C. by DTA and TGA. Although there is considerable information in the literature on the design of DTA and TGA equipment for use up to 1200" C. (6, I d ) , only a few papers are available on the application of these techniques a t higher temperatures (9, 11). EXPERIMENTAL
Materials. Alcoa type A-2 alumina (low iron, -325 mesh, >99% AlzOs),
