E . HIOMS AREN ' in 14 , 6T VE UNCLASSIFIED ORNL . . 2 VAN CULO A SA . IN . e . 635 . . . . V 1 . 1 . ,'t . 17 :: . . YJE ! l RO .12 NY LA * . 2723 1. . . . . .. 19 ! .AVI . LP n . . ..1 .. ... WW. ". TW Hy 26 LAN . . * MIRI A . Trios ORNL-P-630 CONF-805-6 .. NOV 1 3 1964 For Presentation at the Meeting of European-American Nuclear Data Committee Brussels, Belgium, January 18-22, 1965 METHODS USED AT ORNL FOR THE PRECISE DETERMINATION OF PLUTONIUM .. . .. .. Paul F. Thomason . .. Oak Ridge National Laboratory Oak Ridge, Tennessee MASTER .. Controlled-Potential Coulometric Titration of Plutonium .. ..... The man opport Commons Cont ent with other the The application of controlled-potential coulometric titrimetry to the LEGAL NOTICE with this 3 $ PE determination of plutonium was first studied by Scott and Peekema +) and later by Shults. (2) The methat is based on the principle that under suitable conditions plutonium can be electrolytically converted from puts to put* or from Put* to puts with essentially 100% current efficiency. A complete reduction of puts to puts can be accomplished at +0.560 volt vs. S.C.E. and oxidation can be made at +0.880 volt vs. S.C.E. in 1 M HC104. The electrolysis of either reaction is terminated at a cut-off current arred of 30 ua for the cell size and electrode used. The current of either the -- en.. oxidation or reduction reaction can be integrated and plutonium calculated via Faraday's laws of electrolysis (96,487 +2 coulombs per equivalent gram weight). We prefer to integrate the oxidation reaction of puto to put The first slide shows a diagram of the cell used for controlled- potential coulometric titration of plutonium. It is quite similar to the cell shown for the titration of uranium except that it has a large surface platinum gauze used as the working electrode. Actually a larger circular gauze which follows closely the inner perimeter of the 50-ml beaker is a st . Aku .-? ins . XT: Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corporation. ' 3 - . 2. .- ES . X a vion no... ... ................. -2. + now used. The tight fitting cap 18 machined from Teflon. The stirrer in this case 18 a glass rod with a propeller on the bottom for vigorous stirring. The vycor tubes have an electrical resistivity of about 100 ohms when filled with 1 M HNO3 . This method 18 used primarily for accountability analysis of our 80 called "product" samples which usually contain 40 to 60 mg per ml of plutontum in 4.5 M HNO3. They also contain small quantities of iron and uranium, and sometimes traces of reducing impurities such as hydroxyl. amine sulfate and sull'amic acid. These reducing impurities may be destroyed by preliminary heating with HNO3. Iron and uranium do not interfere if proper potentials and electro- lytes are chosen. The next slide shows a coulogram of Q versus applied potential for 5 mg puts and ~1 mg Fe** in HC10, and H2SO4. The Q (readout voltage) is obtained by reducing the applied voltage to a point where current ceases to flow and reading the integrated current (voltage accumulated on the 10 ufa capacitor discussed previously in the uranium paper). This curve shows the reduction or puts can be carried out in the presence of Fe in HC104 at a potential of +0.560 volt vs. S.C.E. Only 1% of Fe*" is reduced at this potential which equals only lug of Fe. In H250, both Put* and Fe* are reduced at +0.3 volt vs. S.C.E. without any plateau in the coulogram where one metal could be - . reduced separately. The next slide shows that puts can also be titrated in 0.5 M HCI, containing 0.02 M sulfanic acid to destroy any nitrites present. The coulogram shows the reduction of Pu** can be done at +0.600 volt with the mid-point of the curve at +0.705 volt vs. S.C.E. Iron reduction occurs at +0.300 volt vs. S.C.E. with mid-point at +0.465 volt. 2 . *- D bi . Tun T I PID Y A INYA . L . AND WHV VARLIJI.... . . . . . .. . Uranium in 1 M HC!.0,-0.02 M NH2S02H has a formal potential of -..1 volt vs. S.C.E. Which 18 sufficiently different from plutonium to preclude the reduction of 102te at +0.560 volt. The next slide shows the steps taken to analyze plutonium "product solutions." A one hundred micro liter sample containing 4 to 6 mg of Pu 18 pipetted into the titration cell and heated by means of a heat lamp with 3 drops of concentrated HNO3 unti). thc puts blue color disappears. This also destroys any reducing material present. Fifteen ml of 1 M HC104-0.02 M NH2SO3H solution are added and degassed with helium for 10 minutes. A preliminary reduction is made at +0.560 volt vs. S.C.E. until a cut-off current of 30 ua is reached. The integrator 18 discharged and an oxidation of Puto to Puti 18 made at +0.880 volt vs. S.C.E. until 30 ua current 18 again reached. The readout voltage is then measured and plutonium calculated by means of the Faraday value. The relative standard deviation is 0.1%. The next slide shows an indirect controlled-potential coulometric titration of plutonium using iron as an intermediate reagent. This method was developed by Shults." Secondary processes are used quite often in constant current coulometric titrations but if an intermediate's couple 18 reversible it is possible to generate an excess of reagent at controlled- potential to accomplish a desired reaction and the excess reagent then back- titrated. The advantage of this method is the fact that a two-electron reaction results which makes the determination twice as sensitive as the regular plutonium product analysis method; also iron interference is eliminated. Pute and puts can be chemically oxidized to puto by means of perchloric acid or argentic oxide. As Pute cannot be electrolytically reduced directly at the working electrode, 0.5 ml of 5 mg/ml Fe* solution 21 1 in 1 M HCl 18 auded as an intermediate reagent when one to five mg of Puto 18 titrated. Either 1 M HC104 or 1 M H290, can be used as the supporting electrolyte solution in this procedure, although we prefer 1 M H2804. Excess Fe** 18 generated from Fe*s at +0.270 volt vs. S.C.E. until about 10--20 meq of excess Fe* has been generated and the read- out voltage 18 measured. Pute is reduced to puth by the generated Fea, also some Pu+9 18 generated at the platinum gauze clectrode at the potential used to reduce Fe+$. Therefore, we have puts, Fet, Fete and possibly some Puti 10n8 in solution. The relative concentrations of these species will depend upon the amount of reduction which has taken place. An oxidation at +0.660 volt ve. S.C.E. is made until a cut-off current of 50 ya is reached. The integrated current is measured from the integrator since it is proportional to the voltage accumulated on the capacitor. The ORNL Q-2005 instrument which we used for this study has a cali. bration factor of 8.1875 coulombs per volt readout or 10.14 mg of Pu per volt for a 2-electron change reaction. Therefore the weight in mg of Pu is obtained from the relationship 10.14 (Q.-22). The relationship of readout voltage and coulombs consumed will vary from instrument to instrument. The method as described has a relative standard deviation of 0.2%. Specially purified plutonium metal of 99.93% purity obtained from Los Alamos Scientific Laboratory is used as a standard to check the Faraday value. Automatic Micro-Potentiometric Titration of Plutonium Another method we use at ORNL when we only have microgram quantities of plutonium 18 & potentiometric titration of puts with ce** solution as the titrant. A special micro-buret was fabricated at ORNL machine shops and 18 shown in the next slide. This buret has a piatinım plunger in contact with the ceric sulfate titrant and an external electrical connec- tion 18 made so that the platinum serves as an in-buret electrode. The micrometer sleeve 18 retracted to the fill mark (at the extreme back of the cylinder) and titrant 18 drem into the buret from the tip by means of a vacuum applied to point 6 on the slide. The buret 18 allowed to fill until titrant is drawn into the transparent vacuum tubing. The vacuum line is disconnected and the buret micrometer drive is turned forward to the zero mark. The buret will deliver a total of 50 ul of the titrant although most of our titrations only use from 20-40 ul of the ~0.1 N Ce( $06)2 solution. The next slide shows a diagrem of the micro-titration cell which is about 115 mm tall with the bottom about 13 mm in diameter. From 0.5 to 1.0 ml of solution containing 100 to 200 ug of plutonium 1n ~1 M H2SO4 made from a 5 mm length of iron wire sealed into a glass tube. A piece of 20-gauge gold wire 18 used as the indicating electrode with the in-buret electrode serving as the reference electrode. The gold wire must be cleaned after each titration as it can be poisoned and become passivated by surface contaminants. The gold wire is cleaned by immer- sion for a few minutes in KaCr207-H2S04 cleaning solution. Polishing with an emery cloth periodically also improves the performance of the electrale. The next slide shows the complete titration assembly with the buret connected to the ORNL Q-945 automatic potentiometric titrator. The titration cell is placed in an open face hood to give some protec- tion when handiling alpha emitting materials while still permitting easy access to the cell. The titration cell 1s raised or lowered by means of an electric Jack. The motor drive of the buret and motor drive of the chart are electrically connected so that the length of the chart 18 proportional to the volume of titrant delivered by the buret. The last slide shows a typical titration curve of 51.5 mg of Fe - - titrated with ~0.06 N Ce(SO4)2, The titration of plutonium has the same forn as this titration curve. The iron is reduced to Fe*2 by means of about 10 ul of chromous sulfate solution, which is a slight excess of cr*2 as shown by the potential going to -1.45 volts vs. in-buret reference, made in a manner that was described in the uranium potentiometric titration method. The titrant delivery is then started and a break in potential occurs when the ce** 3olution oxidizes the excess Cr* in solution. The potential range of the titrator is then changed and the titration continued. The next break occurs when the Fe* 1s uxidized to Fe+s (or Pu+S to Pu**, in the Pu titration) . The breaks are sharp and usually about 200—300 millivolts on the chart. By measuring the length of the chart between the two potential breaks It is possible to calculate the amount of iron or plutonium titrated. This curve shows 12.90 inches of chart for 51.5 ug of Fe which calculates out to be equivalent to 17.1 ug of plutonium per inch of chart. The method can be standardized against pure iron wire or the specially purified plutonium metal (99.93% purity). When titrating 100 to 200 ug of plutonium a relative standard deviation of 0.5% 1s obtained. It 18 possible to titrate mg quantities of Pu with a more concentrated cel sonde titrant and longer chart travel to a precision of 0.1%. ACKNOWLEDGEMENTS The author 18 indebted to W. D. Shults and F. J. Miller for their suggestions. F. J. Miller developed the method for the automatic micro potentiometric titration of plutonium and W. D. Shults worked out the details of the controlled-potential coulometric titration methods for the determination of plutoniun. REFERENCES 1. Scott, F. A., and Peekema, R. M., "Analysis for Plutonium by Controlled-Potential Coulometry," Proc. U. N. International Conference, Peaceful Uses of Atomic Energy, 2nd Geneva, 1958, 28, 573 (1958). 2. Shults, W. D., "Controlled-Potential Coulometric Titration of Plutonium - Application to PRFR Samples," ORNL-2921, April 11, 1960. 3. Shults, W. D., "Coulometric Generation and Back-Titration of Inter- mediate Reagents at Controlled-Potential. Application to the Determiration of Plutonium," Anal. Chem. 33, 15 (1961). -8- LIST OF SLIDES ORNI Number Number Title Diagram of Titration Vessel Assembly LR-DWG 45526 LR-DWG 46560A Characteristics of Coulometric Reduction of ~5 mg Pu(IV) and ~1 mg Fe(III) in HC104 and H2S04 LR-DWG 55261 F w Characteristics of Coulometric Reduction of 250 M8 Pu(IV) and 100 ug Fe(III) in 0.5 M HC1-0.02 M NH2S03H Controlled-Potential Coulometric Titration of Plutonium (Procedure) DWG 64-8469 Plutonium by Indirect C. P. Coulometric Titration LR-JWG 55601 (Procedure) Exploded View of the ORNL Micro-Burette none none Sketch of Titration Vessel Used for potentiometric Determination of Plutonium Titration Assembly for the Determination of Photo 51494 Microgram Quantities of Plutonium Typical Curve for Ceric Sulfate Titration of Iron none **** m . 1: : 9 UNCLASSIFIED ORNL-LR-DWG. 45526 S.C.E. - eee O GAS INLET -- Fo00000000000 TEFLON CAP STIRRER TIR 21 - VYCOR TUBES - (Contain 1 M HNO3) SAMPLE PORT -50 m! LIPLESS BEAKER - PLATINUM GAUZE - DIAGRAM OF TITRATION VESSEL ASSEMBLY SLIDE 1 . . : r.. - - ... ... .. UNCLASSIFIED ORNL-LR-DWG. 46560A . 0.5 0.37 Q~ READOUT, volt A M HCIOA M H2SO4 0.0 0 0 0 0 3 Ecevs S.C.E., volt Characteristics of coulometric reduction of ~5 mg Pu(I) and ~1 mg Fe(II) in HCIO4 and H2S04. SLIDE 2 1ST. . UNCLASSIFIED ORNL-LR-OWG. 55261 0.41 -0.465 Q = READOUT, volt 0.705 800 200 700 600 300 500 S.C.E. Characteristics of coulometric reduction of 250 mg Pu(I) and 100pg Fe (III) in 0.5 M HCI - 0.02 M NH2SO3H. SLIDE 3 Firmainfo mation to be with Aga i nst herbal areas anderinge die winter the parang anda carteira .. w " . UNCI, ASSIFICO ORNI OWO. 04.0469 CONTROLLED-POTENTIAL COULOMETRIC TITRATION OF PLUTONIUM SAMPLE PREPARATION 1. PIPET SAMPLE CONTAINING 4-6 mg OF PU INTO CELL. 2. ADD 1 ml OF CONC. HNO ; EVAPORATE TO NEAR DRYNESS. 3. ADD 15 ml OF IM HCIO,-0.02 M NH,SO3H SOLUTION. TITRATION 1. POSITION CELL; START HELIUM FLOW; START STIRRER; DEAERATE FOR 5 min. 2. REDUCE AUTOMATICALLY AT +0.560 v VS S.C.E. TO CUT-OFF CURRENT OF 30ua. 3. ZERO THE INTEGRATOR. 4. OXIDIZE AUTOMATICALLY AT +0.880 v VS S.C.E. TO CUT-OFF CURRENT OF 3qua. 5. MEASURE READOUT VOLTAGE. 6. CALCULATE WEIGHT OF PU BY MEANS OF THE ELECTRICAL CALIBRATION FACTOR. ::1.11116 af aux RCTI NR. UNCLASSIFIED ORNL-LR-DWG. 55601 PLUTONIUM BY INDIRECT C.P. COULOMETRIC TITRATION [ Anal. Chem. 33, 15(1961) ] Procedure : 4. Prepare Pu(VI), Fe (II) chemically. 2. Generate excess Fe (II) at -0.18 volt. Fe ( II ) ► Fe (II) Pu(VI) + Fe (II) → Pu( N ) + Fe (II) Pu(IV) -Pu (III) + 0.18 volt. 3. Oxidize excess Fe (I), Pu(I) at E Fe (II) → Fe (II) Pu(II) → Pu (V) Net Reaction : Pu(VI) → Pu(V) Precision : 0.2% (95% C.L.). SLIDE 5 @ D DILETTE 2) DIP!: THE SHIELD J SHIELD !!!!1 SPRING TEFLON SEAL O HOSE CO:INOTO DUNGER O CILINDER ODLINGER CONNECTER 10 WASHER IN DIN 12.9LEEVE DO MICRONriTeR BARREL USC 2 E. Vi ® BARREL NUT ® ADJUSTMENT NUT ADJUSTMENT NUT O INNER BODY MICROMETER SLEEVE O SLEEVE CAD SLIDE 6 PLUTONIUM, POTENTIOMETRIC CERIC SULFATE METHOD - Process Methods IX. APPENDICES (Continued) E. Sketch of Titration Vessel Used for potentiometric Determina con 01 Plutonium Insert Buret Here Insert Gold Electrode Here $ 19/38 $ 14/35 8-mm 0.D. Pyrex Tubing To - CO2 Cylinder 8-mm 0.D. Pyrex Tubing Fritted Disc K -13-mm 0.D. Pyrex Tubing Stirring, bar Sample Solution Perfectly flat (Full Scale) SLIDE 7 十一 ​. “ *-- HT 11 中 ​.. 。 比​.. 我​, .. 法 ​HP: “ ” - - it ! - 以太 ​- | ·", - . .. - 。 」 了 ​..., FA. . “ w :: 不过​,, 农业 ​“r 1:11 中 ​ty 量 ​” . . . . 中​, i 一​. fety , 集中 ​1 12月 ​九 ​“ ,, , A 主 ​14 「 (1, 4- 」 mium 14. 事业单 ​MAT 1 其一​, : tri ht * 中年人 ​. 我會 ​. 虽说 ​* 。 * TA 的 ​* * , ” 出 ​40岁以 ​。 了 ​- 名 ​你的心​, . 1 L ' , F, |"" 4 在此​, 发货 ​TAASty :: 一 ​- 、 * | | | | A -- * . 1 * 1 1 --. . 4 . Apr % , , 重 ​. * 中 ​. . * 大学生 ​.. , tf * 非 ​北 ​。 * . * JR : 化 ​.. 小​, 长发发 ​l t . ) . * " s: 4:1} 置 ​: * 19 :14.05 MSN { r , “… ' '''' AAA 14 s 书 ​h : e F 1 :: + : 、 . . fA : * , . 、NR以外​, . : , . , A * * . * ..*'' 11.ru 1. :41 . WWW ii.. * A 中 ​. : : , . . *。 是 ​. - 分 ​** - ***irl :" - - - - 王 ​Arts , . '''. 「,「1111 *': IT firs , l t., LE - 本事​, . : - | 11.1.LT . 1况​, 1 " “ .1" : "" ” 1 . * : . ht ·提高 ​重量 ​Hit It . ' +1.1 Fly el 「 1 4 : , , 1 「 是ut MARRY 重 ​Har":; | : : i.trid 作​比分 ​上車​: - : - I ', ' ' , # .. --! - 但果​. l , 1 售 ​, . 件 ​1 - - 111 普世 ​: ::: , 里 ​L11 在Inc. Ariyaki...… 4, it . : : : : :: . : , "",S ET . 重​,也是 ​I t ' 」 - ": : FANT, eat. 「. r ' .. 13 V 5. . A IP, ', . 1 ASICS: : · A *(.P TT V中 ​'. . . . / '''' 入 ​144 t""" , 中 ​11** SWA 是广​, i 'll.l ! “是 ​。 ,4' 中 ​14 f . '' '' ' ', SLIDE 8 Typical Curve for Ceric Sulfate Titration of Iron TTitration curve for plutonium has the same form) Fe(II)-Fe (II) 0.0515 mg OF Fe TITRATED WITH 0.06 N Ce (504)2 INCHES CHART TRAVEL = 12.90 mg OF PU (0.0515 ) x (239) : 0.0174 INCH OF CHART TRAVEL (12.90) * (55.85) 12.90 INCHES INCHES OF CHART TRAVEL 11 INCH POTENTIAL SHIFT RESULTING FROM CHANGE OF VOLTAGE RANGE- 7 SELECTOR La Cr(II)-Cr(III) BREAK POTENTIAL SLIDE 9 DATE FILMED 12/28/164 ' hy . . 2. 5L. LEGAL NOTICE This report was preparod as an account of Government sponsored work. Neither the United States, nor the Commission, nor any person acting on behalf of the Commission; A. Makes any warranty or representation, expressed or inplied, with respect to the accu- racy, completeness, or usefulness of the information containod in this report, or that the use of any information, apparatus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any information, apparatus, method, or process disclosed in this report. As used in the above, “person acting on behalf of the Commission" includes any em- ployee or contractor of the Commission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. END NE