1、Designation: E 692 00Standard Test Method forDetermining the Content of Cesium-137 in Irradiated NuclearFuels by High-Resolution Gamma-Ray Spectral Analysis1This standard is issued under the fixed designation E 692; the number immediately following the designation indicates the year oforiginal adopt
2、ion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the numberof atoms of137Cs
3、in aqueous solutions of irradiated uraniumand plutonium nuclear fuel. When combined with a method fordetermining the initial number of fissile atoms in the fuel, theresults of this analysis allows atom percent fission (burnup) tobe calculated (1).2The determination of atom percent fission,uranium an
4、d plutonium concentrations, and isotopic abun-dances are covered in Test Methods E 267 and E 321.1.2137Cs is not suitable as a fission monitor for samples thatmay have lost cesium during reactor operation. For example, alarge temperature gradient enhances137Cs migration from thefuel region to cooler
5、 regions such as the radial fuel-clad gap,or, to a lesser extent, towards the axial fuel end.1.3 A nonuniform137Cs distribution should alert theanalyst to the potential loss of the fission product nuclide. The137Cs distribution may be ascertained by an axial gamma-rayscan of the fuel element to be a
6、ssayed. In a mixed-oxide fuel,comparison of the137Cs distribution with the distribution ofnonmigrating fission-product nuclides such as95Zr or144Cewould indicate the relative degree of137Cs migration.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its
7、 use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:E 170 Terminology Relating to Radiation Measurementsand Dosimetry3E 181 G
8、eneral Methods for Detector Calibration and Analy-sis of Radionuclides3E 219 Test Method for Atom Percent Fission in UraniumFuel (Radiochemical Method)3E 267 Test Method for Uranium and Plutonium Concentra-tions and Isotopic Abundances3E 321 Test Method for Atom Percent Fission in UraniumAnd Plutoni
9、um Fuel (Neodymium-148 Method)33. Summary of Test Method3.1137Cs is assayed by measuring the 6624keV gamma-rayemission rate from the isomeric transition of its metastable 2.65min137mBa daughter, using a high-resolution germaniumdetector and multichannel pulse-height analyzer. Refer to TestMethods E
10、181.3.2 The number of atoms of137Cs in a sample is computedfrom the measured net gamma-ray count rate relative to themeasured net gamma-ray count rate from a standard137Cssolution.4. Significance and Use4.1 This test method uses a high-resolution gamma-rayspectrometer as a basis for measuring the ga
11、mma-ray emissionrate of137Cs-137mBa in a dilute nitric acid solution containing10 mg/L of cesium carrier. No chemical separation of thecesium from the dissolved-fuel solution is required. Theprincipal steps consist of diluting a weighed aliquot of thedissolved-fuel solution with a known mass of 1 M
12、nitric acid(HNO3) and measuring the 662 keV gamma-ray count ratefrom the sample, then measuring the 662 keV gamma-raycount rate from a standard source that has the same physicalform and counting geometry as the sample.4.2 The amount of fuel sample required for the analysis issmall. For a sample cont
13、aining 1 mg of fuel irradiated to oneatom percent fission, a net count rate of approximately 103counts per second will be observed for a counting geometrythat yields a full-energy peak efficiency fraction of 1 3 10-3.The advantage of this small amount of sample is that theconcentration of fuel mater
14、ial can be kept at levels well below1 g/L, which results in negligible self-absorption in the samplealiquot and a small radiation hazard to the analyst.1This test method is under the jurisdiction of ASTM Committee E-10 on NuclearTechnology and Applications and is the direct responsibility of Subcomm
15、itteeE10.05 on Nuclear Radiation Metrology.Current edition approved March 10, 2000. Published May 2000. Originallypublished as E 692-79. Last previous edition E 692-98.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3Annual Book of ASTM Standards, V
16、ol 12.02.4The energy of the gamma ray is more precisely given in Reference (2) as661.657 keV. For simplicity, all citations of this energy in this standard will be givenas 662 keV.5The half-life of this state is more precisely given in Reference (3) as 2.552 min.For simplicity, all citations of this
17、 half-life listed in this standard will be given as 2.6min.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.5. Precautions5.1 Interferences from other gamma-emitting fission prod-ucts are lessened by the use of a germanium detector with aminimum resolution of 3
18、 keV full-width at half-maximum(FWHM) at 1332 keV, and by allowing 4 months or more forthe sample to decay prior to measurement (4). Under theseconditions, the gamma rays nearest to the 662 keV gamma rayof137mBa will be the 637 keV gamma ray of125Sb and the697 keV gamma ray of144Pr.5.2 A slight comp
19、lication of this test method is that the 662keV gamma ray is superimposed on the Compton edge fromthe 766 keV gamma ray of95Nb and from the 796 keV gammaray of134Cs, as shown in Fig. 1.5.3 This test method requires accurately weighing an aliquotof the sample of fuel material containing sufficient137
20、Cs-137mBa activity into a sample vial. In order to achieve theprecision of which this test method is capable, the analystshould exercise great care when preparing the sample. Toreduce the uncertainty associated with the sample quantity,aliquots should be prepared by weighing to an accuracy ofbetter
21、than 0.2 %. Weighing also reduces the calculation task,because in the case of burnup analysis, the quantity ofheavy-element atoms in the sample will have been determinedon a mass-aliquot basis. The aliquot of sample solution shouldcontain a weight of fuel sample of not less than 0.1 g weighedto an a
22、ccuracy of 0.01 mg, and is to be diluted to the same totalmass as the working standard. Uncertainties caused by slightvariations in the counting-geometry among samples are negli-gible provided that the masses of the individual diluted samplesare within 6 0.01 g of each other.5.4 The preparation of t
23、he137Cs reference standard shouldreceive particular attention. Preferably, the number of137Csatoms per gram of standard should have been determined byisotope-dilution mass spectrometry. An aliquot of not less than0.1 g of the standard solution, weighed to 6 0.1 mg, is dilutedto total mass of 10.00 g
24、 with 1 M HNO3in a sample vial, whichis then flame-sealed. A series of working standards withdifferent concentrations should be prepared so that a workingstandard may be selected that will have approximately thesame number of137Cs atoms as the sample to be measured.6. Apparatus6.1 Germanium Detector
25、, with minimum resolution capa-bility of 3 keV FWHM at 1332 keV, and associated electronics.6.2 Multichannel Pulse-Height Analyzer, capable of a con-version ratio of 1 keV per channel (channel number versusgamma-ray energy in kiloelectronvolts).7. Reagents and Materials7.1 Cesium-137 Standard Soluti
26、onNBS SRM 4233, cer-tified for137Cs atoms per gram contents.67.2 Dilution Reagent1M nitric acid (HNO3), containing10 mg/L of natural cesium carrier. Dissolve 15 mg of oven-dried (140C) reagent-grade cesium nitrate (CsNO3) per litre of1 M HNO3. Mix well.7.3 Vials, flame-sealable, 20-mL standards ampo
27、ules.77.4 Vials for Samples, 20-mL nominal capacity.86Available from the U.S. Department of Commerce, National Institute ofStandards and Technology, Washington, DC 20234.7Vials, available as Item No. 5844 from Wheaton Glass Co., Millville, NJ, ortheir equivalent have been found satisfactory.8Wheaton
28、 Crystal Lite glass liquid-scintillation counting vials, available fromWheaton Glass Co., Millville, NJ, or their equivalent have been found satisfactory.FIG. 1 Gamma-Ray Spectrum of a (Pu,U)O2Fuel, Irradiated to 6 Atom % Fission, and Decayed for 7 MonthsE 6922NOTE 1Vials used for samples and standa
29、rds should have the samedimensions.8. Procedure8.1 Weigh into a tared sample vial a sufficient aliquot of thesolution containing the dissolved fuel to obtain 10 to 250counts per second in the 662 keV peak. Weigh the sample massto the nearest 0.1 mg and record.8.2 Add sufficient 1 M HNO3to the sample
30、 vial to give atotal (sample-plus-acid solution) mass of 10.00 6 0.01 g.8.3 Seal the vial with the cap and mix the solution by gentleswirling.8.4 Place the sample vial in an exactlyreproducible posi-tion relative to the germanium detector so that a count rate of10 to 250 s-1in the 662 keV peak is ob
31、tained without exceedinga gross count rate of 3000 s-1.8.5 Accumulate sufficient counts in the 662 keV peak toachieve the desired precision. The standard deviation of thesample net peak counts is equal to the square root of the sumof the squares of the standard deviations of the countsassociated wit
32、h the Compton edge and background and withthe gross peak counts. Thus, when the Compton and back-ground counts comprise, for example, up to 50 % of the grosspeak counts, then a total accumulation of 100 000 counts willbe necessary to obtain a 1 % standard deviation. The net countsin the 662 keV peak
33、 should be greater than the Compton-background correction; otherwise one should use Test MethodE 321, which involves the chemical separation of cesium fromother radioactive interferences. The analyst must determine theoptimum counting time needed to achieve the desired accuracyand precision.8.6 Repl
34、ace the sample vial with the standard, and count itto the same precision.8.7 Determine the net counts in the 662 keV peak in boththe sample spectrum and in the standard spectrum.8.8 Calculate the number of137Cs atoms in the sample fromthe ratio of the 662-ke V-peak countrates and the knownnumber of1
35、37Cs atoms in the standard.8.9 For determination of atom percent fission from thenumber of137Cs atoms in the sample, refer to Test MethodE 219 and the current compilation of fission yields (1).9. Precision and Bias9.1 The estimated precision in an interlaboratory compari-son with seven participating
36、 laboratories was 0.45 % relativestandard deviation.9.2 Two irradiated fuel sample solutions and a pure137Csreference standard, each in a sealed ampoule, were circulatedamong the participating laboratories. The relative standarddeviation for sample 1, for a single laboratory was 0.40 % andfor sample
37、 2 was 0.45 %. Sample 1 was from a uraniumdioxide (UO2) fuel irradiated to 3 atom % fission and decayedfor 1.5 years. Sample 2 was from a mixed oxide (Pu,U)O2fuelirradiated to a 6 atom % fission and decayed for 7 months. Aportion of the gamma-ray spectrum of sample 2 is shown inFig. 1.NOTE 2Measurem
38、ent uncertainty is described by a precision and biasstatement in this standard. Another acceptable approach is to use Type Aand Type B uncertainty components (5, 6). The Type A/B uncertaintyspecification is now used in the International Organization for Standard-ization (ISO) standards and this appr
39、oach can be expected to play a moreprominent role in future uncertainty analyses.REFERENCES(1) Rider, B. F, and Meek. M. E. ENDF/BVE, NEDO-12154-2E, June1978.(2) “Evaluated Nuclear Structure Data File (ENSDF),” maintained by theNational Nuclear Data Center (NNDC), Brookhaven National Labo-ratory, on
40、 behalf of the International Network for Nuclear StructureData Evaluation, status as of September 8, 1997.(3) “Nuclear Wallet Cards,” National Nuclear Data Center (NNDC),Brookhaven National Laboratory, prepared by J. K. Tuli, July 1995.(4) Matlack, G. M., Buzzelli, G., and Larsen, R. P., “Cs-137 Det
41、ermina-tion for Burnup Measurements by Gamma-Ray Spectrometry,” Libby/Cockcroft Exchange Meeting on Burnup, Los Alamos Scientific Lab.,Los Alamos, NM, June 9-11, 1969, Paper No. 37, p. 181.(5) Taylor, B.N., Kuyatt, C.E., “Guidelines for Evaluating and Expressingthe Uncertainty of NIST Measurement Re
42、sults,” NIST Technical Note1297, National Institute of Standards and Technology, Gaithersburg,MD, 1994.(6) “Guide to the Expression of Uncertainty in Measurement,” Interna-tional Organization for Standardization, 1993, ISBN 92-67-10188-9.The American Society for Testing and Materials takes no positi
43、on respecting the validity of any patent rights asserted in connectionwith any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any suchpatent rights, and the risk of infringement of such rights, are entirely their own responsibility
44、.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM
45、Headquarters. Your comments will receive careful consideration at a meeting of the responsibletechnical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make yourviews known to the ASTM Committee on Standards, at the address shown below.This
46、 standard is copyrighted by ASTM, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the above address or at610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website (www.astm.org).E 6923
