1、Designation: C1267 11Standard Test Method forUranium by Iron (II) Reduction in Phosphoric Acid Followedby Chromium (VI) Titration in the Presence of Vanadium1This standard is issued under the fixed designation C1267; the number immediately following the designation indicates the year oforiginal adop
2、tion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method, commonly referred to as the ModifiedDavies and Gray te
3、chnique, covers the titration of uranium inproduct, fuel, and scrap materials after the material is dis-solved. The test method is versatile and has been ruggednesstested. With appropriate sample preparation, this test methodcan give precise and unbiased uranium assays over a widevariety of material
4、 types (1, 2).2Details of the titrationprocedure in the presence of plutonium with appropriatemodifications are given in Test Method C1204.1.2 Uranium levels titrated are usually 20 to 50 mg, but upto 200 mg uranium can be titrated using the reagent volumesstated in this test method.1.3 The values s
5、tated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety
6、and health practices and determine the applica-bility of regulatory limitations prior to use. For specificsafeguard and safety precaution statements, see Section 4.2. Referenced Documents2.1 ASTM Standards:3C696 Test Methods for Chemical, Mass Spectrometric, andSpectrochemical Analysis of Nuclear-Gr
7、ade Uranium Di-oxide Powders and PelletsC799 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and Radiochemical Analysis ofNuclear-Grade Uranyl Nitrate SolutionsC1128 Guide for Preparation of Working Reference Mate-rials for Use in Analysis of Nuclear Fuel Cycle MaterialsC1204
8、 Test Method for Uranium in Presence of Plutoniumby Iron(II) Reduction in Phosphoric Acid Followed byChromium(VI) TitrationC1346 Practice for Dissolution of UF6from P-10 Tubes,C1347 Practice for Preparation and Dissolution of UraniumMaterials for Analysis2.2 NIST Standard:4SRM 136e Potassium Dichrom
9、ate (Oxidimetric Standard)2.3 NBL Standard:5CRM 112A Uranium Metal Standard3. Summary of Test Method3.1 Samples are prepared by dissolution techniques detailedin Practices C1346, C1347, or Refs (2), (3), and (4). Appro-priate uncertainties for sampling and weight determinationshould be applied to th
10、e overall precision and bias calculationsfor the final result. Aliquants containing 20 to 200 mg ofuranium are prepared by weight. The sample is fumed todryness after the appropriate acid treatment. The sample isdissolved in dilute nitric acid or water prior to titration.3.2 Uranium is reduced to ur
11、anium(IV) by excess iron(II) inconcentrated phosphoric acid (H3PO4) containing sulfamicacid. The excess iron(II) is selectively oxidized by nitric acid(HNO3) in the presence of a molybdenum(VI) catalyst. Afterthe addition of a vanadium(IV) solution, the uranium(IV) istitrated with chromium(VI) to a
12、potentiometric end point.3.3 The chromium(VI) titrant may be delivered manually ona weight or on a volumetric basis as specified by the facilitytitration procedure.3.3.1 If the titrant is delivered on a volumetric basis,corrections to the volume of titrant may be needed to adjust forthe difference b
13、etween the temperature of preparation and theambient temperature.3.3.2 Automated titrators are facility specific and are notexplicitly addressed in this test method. However, automatedtitrators which have comparable bias and precision may beused.1This test method is under the jurisdiction ofASTM Com
14、mittee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved June 1, 2011. Published June 2011. Originallyapproved in 1994. Last previous edition approved in 2006 as C1267 06. DOI:10.1520/C1267-11.2The boldface numbers in parenthe
15、ses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM websit
16、e.4Available from National Institute of Standards and Technology (NIST), 100Bureau Dr., Stop 1070, Gaithersburg, MD 20899-1070, http:/www.nist.gov.5New Brunswick Laboratory (NBL) Certified Reference Materials Catalog (U.S.Department of Energy), http:/www.nbl.doe.gov.1Copyright ASTM International, 10
17、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.3.3 There is an alternate, high precision (;0.005 % RSD)modified Davies and Gray titration, which is similar to themethod covered in this procedure. In the high precisionmethod, the amount of uranium titrated is incr
18、eased and about90 % of the titrant is delivered on a solid weight basis followedby titration to the end point with a dilute titrant. Details of thisalternate method are available in Ref (5).4. Significance and Use4.1 Factors governing selection of a method for the deter-mination of uranium include a
19、vailable quantity of sample,homogeneity of material sampled, sample purity, desired levelof reliability, and facility available equipment.4.2 This uranium assay method is referenced in the TestMethods for Chemical, Mass Spectrometric, and Spectro-chemical Analysis of Nuclear-Grade Uranium Dioxide Po
20、w-ders and Pellets (Test Methods C696) and in the Test Methodsfor Chemical, Mass Spectrometric, and Spectrochemical,Nuclear, and RadiochemicalAnalysis of Nuclear-Grade UranylNitrate Solutions (Test Methods C799). This uranium assaymethod may also be used for uranium hexafluoride anduranium ore conce
21、ntrate. This test method determines 20 to200 mg of uranium; is applicable to product, fuel, and scrapmaterial after the material is dissolved; is tolerant towards mostmetallic impurity elements usually specified in product andfuel; and uses no special equipment.4.3 The ruggedness of the titration me
22、thod has been studiedfor both the volumetric (6) and the weight (7) titration ofuranium with dichromate.4.4 Committee C26 Safeguards Statement:4.4.1 The materials (nuclear grade uranium in product, fuel,and scrap) to which this test method applies are subject tonuclear safeguard regulations governin
23、g their possession anduse. The analytical method in this standard meets U.S. Depart-ment of Energy guidelines for acceptability of a measurementmethod for generation of safeguards accountability measure-ment data.4.4.2 When used in conjunction with the appropriate certi-fied reference materials (SRM
24、6or CRM), this procedure candemonstrate traceability to the national measurement base.However, use of the test method does not automaticallyguarantee regulatory acceptance of the resulting safeguardsmeasurements. It remains the sole responsibility of the user ofthis test method to assure that its ap
25、plication to safeguards hasthe approval of the proper regulatory authorities.5. Interferences5.1 Interfering elements are not generally present in productand fuel material in quantities which cause interference in thetitration.5.1.1 Of the metallic impurity elements usually included inspecifications
26、 for product and fuel, silver, manganese, andvanadium (in the V oxidation state) interfere when present inamounts of 10 mg or greater of impurity per 100 mg ofuranium (2, 8).5.1.2 Silver and vanadium (in the V oxidation state) causepositive bias when present in milligram quantities in thesample. The
27、 aliquant treatment adjusts the oxidation state ofany vanadium(V) present in the sample (2). To remove silver,the sample must be treated prior to titration (8).5.1.3 Manganese was originally found to cause a negativebias (2), but this bias is eliminated when the titration aliquantpreparation procedu
28、re is followed as given (9, 10) in thistitrimetric method.5.2 Interferences with the Modified Davies and Gray titra-tion, which may be present in some uranium materials, havebeen systematically studied.5.2.1 The non-interference of copper, titanium, cobalt,nickel, cerium, and samarium was demonstrat
29、ed (11) at the 50mg impurity level for 100 mg of uranium.5.2.2 The effects of the following elements in milligramquantities were studied: silver, gold, lead, iodine, arsenic,antimony, and bismuth (8).5.2.2.1 Gold, lead, arsenic(V), antimony(V), and bismuthdo not interfere when present in amounts of
30、10 mg for 100 mgof uranium.5.2.2.2 Silver, iodine, arsenic(III), and antimony(III) inter-fere seriously in the determination of uranium and must beeliminated prior to titration.5.2.3 The effects of impurities on the titration of uraniumcontinued with the platinum metals (ruthenium, rhodium,palladium
31、, osmium, iridium, and platinum), chloride, bromide(12), fluoride (13), and technetium (14).5.2.3.1 Ruthenium, palladium, osmium, iridium, and plati-num cause serious positive errors in the determination ofuranium. Rhodium alone among the platinum metals does notcause any significant error.5.2.3.2 C
32、hloride and bromide interfere with the assaythrough their effect on the platinum indicator electrode.5.2.3.3 Small amounts of fluoride, less than 400 mg ashydrofluoric acid (HF) or 600 mg if HNO3is present, can betolerated by the titration.5.2.3.4 Technicium, found in high temperature reactor grader
33、ecycle (htgr) fuel, interferes with the titration and must beremoved before titration.5.3 The removal of certain interferences in the modifiedDavies and Gray titration has also been studied.5.3.1 The initial fuming of titration aliquants with sulfuricacid removes impurity elements such as the halide
34、s and volatilemetallic elements (2, 12, 13).5.3.2 Arsenic(III) and antimony(III) can be eliminated inthe H3PO4by potassium dichromate (K2Cr2O7) oxidation priorto its addition to the titration medium (8).5.3.3 Elimination of interferences in the titration by mer-cury, platinum, and palladium by means
35、 of a copper columnwas evaluated (15).5.3.4 Elimination of interferences by solvent extraction ofthe uranium from the impurities has also been studied (16).5.4 A list of impurities with brief references to their treat-ment for elimination is given in Table A1.1 in Annex A1, andthe details are given
36、in Refs 2, 8, 9, 10, and 12-16.6SRM is a registered trademark.C1267 1126. Apparatus6.1 Buret, polyethylene bottle (preparation instructions canbe found in Appendix X1), glass weight, or glass volumetric.6.2 pH Meter, with indicator (a 16-gauge platinum wire hasbeen found to be satisfactory) and refe
37、rence (saturated calomelhas been found to be satisfactory) electrodes.6.2.1 The indicator electrode should be changed or cleanedif there is a titration problem such as less distinct than normalend point break or end point drift, or, if desired, prior to usewhen more than a week has passed since its
38、last use. Suggestedcleaning procedures for platinum wire electrodes are detailedin Appendix X2.6.2.2 Asbestos and glass bead tipped saturated calomelelectrodes can be placed directly in the titration solution. Glassfrit tipped saturated calomel electrodes may have a faster leakrate and may need to b
39、e used with a separator tube containingthe electrolyte to prevent titration problems due to chloride.6.2.3 The reference electrode should be covered with arubber tip or submerged in a solution (saturated potassiumchloride solution for the calomel electrode) for overnightstorage.6.3 Magnetic Stirrer
40、and TFE-Fluorocarbon Coated Mag-net.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specific
41、ations are available.7Other grades of reagentsmay be used, provided it is first ascertained that the reagent isof sufficiently high purity to permit its use without lesseningthe accuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mea
42、n laboratory accepteddemineralized or deionized water.7.3 Ferrous Sulfate Heptahydrate (FeSO47 H2O, 1.0 M)Add 100 mL of sulfuric acid (H2SO4, sp gr 1.84) to 750 mL ofwater as the solution is stirred.Add 280 g of FeSO47 H2O, anddilute the solution to 1 L with water. Prepare the FeSO47 H2Oreagent fres
43、h, weekly. See the Note 5 in 10.8 on combinationof this reagent with the H3PO4.7.4 Nitric Acid (HNO3, 8 M)Add 500 mL of HNO3(sp gr1.42) to 10 % Au Reduce the gold to metal and separate (8).Am, Sb, As, Br, Cl, Fe, Au, Pb, Ir, Mn, Hg, Mo,Np, Os, Pd, Pt, Pu, Ru, Ag, Th, Sn, V, ZrUse the tributyl phosph
44、ate/carbon tetrachloride extraction technique (16). Alternate solvents such as dodecaneare now used.AThe potassium dichromate oxidizes these elements to a non-interfering oxidation state which the ferrous ion is not capable of reducing.C1267 118X2. PLATINUM WIRE ELECTRODE TREATMENTSX2.1 A routine pl
45、atinum wire electrode cleaning treatmentand the treatment for restoring fast response to a sluggishplatinum electrode is flaming to white heat with immediateimmersion in concentrated nitric acid; the process is usuallydone at least two times.X2.2 An alternate cleaning method for the platinum wireele
46、ctrodes is to soak the electrode in hydrofluoric acid prior toflaming and nitric acid immersion as detailed in X2.1.X2.3 If the analyses of standards show increasing bias overthe days analyses after routine cleaning, for several consecu-tive days, a sodium bisulfate fusion of the platinum wireelectr
47、ode may be needed.After the sodium bisulfate fusion andflaming, again perform the routine cleaning in X2.1.X3. DICHROMATE SOLUTION STANDARDIZATIONX3.1 Standardize reagent grade or better potassium dichro-mate against CRM 112-A uranium metal or its equivalent (seeAppendix X4).X3.2 The standard deviat
48、ion of the mean for the potassiumdichromate standardization (s/=n ) should be well within theaccepted laboratory error limits for the uranium titration whenn = 10. Example: To maintain an accepted laboratory precisionon the uranium titration of s = 0.10, the recommended accept-able precision on the
49、potassium dichromate standardization iss = 0.05 for n = 10 so that the accuracy of the potassiumdichromate standard solution will have a minimal effect on thetitration results.X4. DISSOLUTION OF URANIUM METALX4.1 The following method has been used successfully forthe dissolution of approximately 40 g of uranium metal forwhich the cleaned and dried weight of the uranium metal hasbeen accurately determined. The surface of the uranium metal(CRM 112-A or its equivalent) shall be cleaned following theinstructions on the certificate.X4.2 Place the metal in a dry weighed 2-L fl
