1、Designation: C 1514 08Standard Test Method forMeasurement of235U Fraction Using Enrichment MeterPrinciple1This standard is issued under the fixed designation C 1514; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last
2、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 covers the quantitative determinationof the fraction of235U in uranium using measurement of the185.7 keV g
3、amma-ray produced during the decay of235U.1.2 This test method is applicable to items containinghomogeneous uranium-bearing materials of known chemicalcomposition in which the compound is considered infinitelythick with respect to 185.7 keV gamma-rays.1.3 This test method can be used for the entire
4、range of235Ufraction as a weight percent, from depleted (0.2 %235U) tohighly enriched (97.5 %235U).1.4 Measurement of items that have not reached secularequilibrium between238U and234Th may not produce thestated bias when low-resolution detectors are used with thecomputational method listed in Annex
5、 A2.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard may involve hazardous materials, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with
6、itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 1030 Test Method for Determination of Plutonium Isoto-pic Composition
7、 by Gamma-Ray SpectrometryC 1490 Guide for the Selection, Training and Qualificationof Nondestructive Assay (NDA) PersonnelC 1592 Guide for Nondestructive Assay MeasurementsC26.10 Terminology Guide2.2 ANSI Standard:N42.14 Calibration and Use of Germanium Spectrometersfor the Measurement of Gamma-Ray
8、 Emission Rates ofRadionuclides33. Terminology3.1 For definitions of terms used in this test method, refer toTerminology C26.10.4. Summary of Test Method4.1 The test method consists of measuring the emission rateof 185.7 keV gamma-rays from an item in a controlledgeometry and correlating that emissi
9、on rate with the enrich-ment of the uranium contained in the item.4.2 Calibration is achieved using reference materials ofknown enrichment. Corrections are made for attenuating ma-terials present between the uranium-bearing material and thedetector and for chemical compounds different from thecalibr
10、ation reference materials used for calibration.4.3 The measured items must completely fill the field ofview of the detector, and must contain a uranium-bearingmaterial which is infinitely thick with respect to the 185.7 keVgamma-ray. If the field of view is not filled, a correction factormust be app
11、lied.5. Significance and Use5.1 The enrichment meter principle provides a nondestruc-tive measurement of the235U fraction of uranium-bearingitems. Sampling is not required and no waste is generated,minimizing exposure to hazardous materials and resulting inreduced sampling error.5.2 This method reli
12、es on a fixed and controlled geometry.The uranium-bearing materials in the measured items andcalibration reference materials used for calibration must fill thedetector field of view.5.3 Use of a low resolution detector (for example, NaIdetector) to measure uranium with235U fraction approximately10 %
13、 which is contained in a thin-walled container can provide1This test method is under the jurisdiction ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on NonDestructive Assay.Current edition approved July 1, 2008. Published August 2008. Originallyappr
14、oved in 2002. Last previous edition approved in 2002 as C 1514 02.2For 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 web
15、site.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.a rapid (typically 100 s), easily portable measuremen
16、t systemwith precision of 0.6 % and bias of less than 1 %.5.4 Use of a high resolution detector (for example, high-purity germanium) can provide measurement with a precisionbetter than 0.2 % and a bias less than 1 % within a 300-smeasurement time when measuring uranium with235U fractionin the range
17、of 0.711 % or above which is contained inthin-walled containers.5.5 In order to obtain optimum results using this method,the chemical composition of the item must be well known, thecontainer wall must permit transmission of the 185.7 keVgamma-ray, and the uranium-bearing material within the itemmust
18、 be infinitely thick with respect to the 185.7 keV gamma-ray. All items must be in identical containers or must have aknown container wall thickness and composition.5.6 Items to be measured must be homogeneous withrespect to both235U fraction and chemical composition.5.7 When measuring items, using
19、low-resolution detectors,in thin-walled containers that have not reached secular equi-librium (more than about 120 days after processing), either themethod should not be used, additional corrections should bemade to account for the age of the uranium, or high-resolutionmeasurements should be perform
20、ed.5.8 The method is often used as a enrichment verificationtechnique.6. Interferences6.1 Appropriate corrections must be made for attenuatingmaterials present between the uranium-bearing material andthe detector. Inappropriate correction for this effect can resultin significant biases.6.2 Incorrect
21、 knowledge of chemical form of the uranium-bearing materials can result in a bias.6.3 Depending on the dead-time correction method used,excessive dead time can cause errors in live time correctionand, thus, result in a measurement bias. Excessive dead timecan usually be eliminated by modifications t
22、o the detectorcollimator and aperture.6.4 Background gamma-rays near 185.7 keV can result in abias. Table 1 is a list of interfering gamma-rays which maycause an interference.6.5 Any impurities present in the measured items must behomogeneously distributed and well characterized. The pres-ence of im
23、purities, at concentrations which can measurablyattenuate the 185.7 keV gamma-ray and which are not ac-counted for will result in a bias.6.6 The presence of radioactive impurities can affect thedetermination of the 185.7 keV peak area. This type ofinterference is most often encountered in low-resolu
24、tion mea-surement, but can affect high-resolution measurements.6.7 Other factors, such as the paint on the outside of thecylinders and the condition of the cylinder inner walls afterexposure to UF6, may affect the precision and bias for both theNaI and the HPGe measurement methods.7. Apparatus7.1 Ga
25、mma-Ray Detector SystemGeneral guidelines forselection of detectors and signal-processing electronics arediscussed in Guide C 1592, Test Method C 1030, and ANSIstandard N42.14. Refer to the References section for a list ofother recommended references (1).4This system typicallyconsists of a gamma-ray
26、 detector, spectroscopy grade ampli-fier, high-voltage bias supply, multi-channel analyzer, anddetector collimator. The system may also include detectorbackshielding, an ultrasonic thickness gauge, an oscilloscope, aspectrum stabilizer, a computer, and a printer.7.2 A high-resolution detector system
27、 or a low-resolutiondetector system should be selected, depending on precision andbias requirements for the measurements. Additional detectorselection considerations are measurement time, cost, and easeof use. High-resolution detector systems are generally larger,heavier, and more costly than low-re
28、solution detector systems.In addition, the cost of high-resolution detectors is significantlyhigher (roughly an order of magnitude) than the cost oflow-resolution detectors. High-resolution systems, however,provide better results than low-resolution systems, and elimi-nate some interferences.7.2.1 H
29、igh-Resolution DetectorA high-resolution detec-tor with a resolution of 1200 eV or better, full width at halfmaximum, at 122 keV is recommended. Either a planar orcoaxial detector can be used, although excessive dead time canresult if a coaxial detector with high (15 %) efficiency is used.The select
30、ed detector should be of sufficient size (including acombination of surface area and thickness) to provide thedesired counting-statistics based uncertainty within a reason-able counting time.7.2.2 Low-Resolution DetectorA low-resolution detectorwith the following specifications is recommended: a 5-c
31、mdiam, 1.25-cm thick or larger detector with a resolution of15 % or better at 122 keV.7.2.3 Collimator and Shield AssemblyThe detector colli-mator and shield assembly must be of sufficient thickness toattenuate in excess of 99.9 % of the 185.7 keV gamma-raysincident upon it. The detector collimator
32、must also block inexcess of 99.9 % of the gamma-rays incident upon it and theaperture must restrict the field of view of the detector so thatthe uranium in the measured items and calibration referencematerials used for calibration completely fill the detector fieldof view. A filter (typically fabric
33、ated from cadmium or tin)may, optionally, be included to reduce the intensity of gamma-induced X rays from the collimator and shield assembly.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.TABLE 1 Interfering Gamma-RaysIsotope ParentGamma-Ray Energy(k
34、eV)Measurement Affected226Ra N/A 185.9 High Resolution,Low Resolution212Pb232U 238.6 Low Resolution224Ra232U 241.0 Low Resolution233Pa237Np 300.1 Low Resolution233Pa237Np 311.9 Low Resolution234Th238U Bremsstrahlung Low Resolution99Tc N/A Bremsstrahlung Low ResolutionC15140827.3 Preparation of Appar
35、atus:7.3.1 Setup apparatus and set parameters according tomanufacturer instructions or site operating procedures.8. Hazards8.1 Gamma-ray detectors may use power-supply voltages ashigh as 5 kV. Appropriate precautions should be taken whenusing, assembling, and disassembling these systems.8.2 Collimat
36、ors and shielding may use materials (for ex-ample, lead and cadmium) which are considered hazardousand/or toxic and can be physically heavy and difficult tomaneuver. Proper care in their use and disposal are required.8.3 Uranium-bearing materials present both chemical andradiological hazards. The an
37、alyst should be aware of thesehazards and take appropriate precautions.9. Calibration9.1 Two types of reference materials are typically used forperforming calibration measurements: (1) certified referencematerials, and (2) secondary reference materials. Containers inthe same configuration as the ite
38、ms to be measured arepreferred.9.1.1 Certified reference materials are commercially avail-able which have been fabricated for the primary purpose ofcalibration of gamma-ray systems for enrichment measure-ments using the enrichment meter principle.9.1.2 Secondary reference materials can be fabricated
39、 byanalyzing for enrichment using destructive analysis techniqueswhich have been calibrated with a traceable reference material.9.2 Fill the field of view for the collimated detector, with theuranium in the reference material.9.3 Measure the reference material for a sufficient amountof time to obtai
40、n the desired precision for the net peak area.The precision for the net peak area should be smaller (a factorof ten is recommended) than the target overall measurementsystem uncertainty.9.4 Record the identifier for the measured item, the type ofuranium-bearing material contained in the item, the co
41、untingtime used, the net peak area and its uncertainty (or theinformation needed to compute the net peak area and itsuncertainty), and the wall thickness and material. Other infor-mation can be recorded as desired. The area for the 185.7 keVpeak can be determined using peak fitting or regions of int
42、erest.If regions of interest are used to determine the area of the 185.7keV peak, record the gross counts for each region to be used.9.5 Repeat steps 9.2-9.4 for other reference materials. Themeasurement of at least one additional item (total of two) isrecommended for calibration of high-resolution
43、systems. Themeasurement of at least two additional items (total of three) isrecommended for calibration of low-resolution systems. Ifrequired by regulations, the enrichment of the reference mate-rials used may need to span the range of anticipated enrich-ments for items to be measured. Use of the me
44、thod outside therange within which it was calibrated is possible due to thelinearity of the calibration, but measurement uncertainty mustbe considered.9.6 Determine the calibration constants and their uncertain-ties using methods shown in Annex A1 and Annex A2,asapplicable to the method chosen for p
45、eak area determination.10. Procedure10.1 Good measurement practice includes the measurementof an item used as a control source (refer to Guide C 1592).10.2 The uranium-bearing material within the measureditem must completely fill the field of view of the collimateddetector in the geometry used for c
46、alibration.10.3 Precision for the net peak area should be adequate tomeet data quality objectives.10.4 Assess the peak background at the 185.7 KeV mea-surement environment.10.5 The area for the 185.7 keV peak must be determinedusing the same method as was used for calibration (peak fittingor regions
47、 of interest). Refer to Table 1 for possible interfer-ences.10.6 Obtain the wall thickness, and material compositionand density for the items container.10.7 Document the identifier for the measured item, thechemical form of uranium-bearing material contained in theitem, the counting time used, the n
48、et peak area and itsuncertainty (or the information needed to compute the net peakarea and its uncertainty), and the wall thickness and material.Other information can be recorded as desired.10.8 Compute the attenuation correction factor and itsuncertainty using equations shown in Annex A1.10.9 Use a
49、ppropriate corrections to account for differentchemical forms verses that used during calibration. See Refer-ences (3) and (4).10.10 Compute the enrichment and the measurement uncer-tainty using equations shown in Annex A1 or Annex A2,asappropriate.11. Precision and Bias11.1 Precision and bias are dependent on several factors,including (but not limited to): measurement time, accuracy ofwall thickness correction factor determination, wall thickness,purity of the measured items, collimation, and calibrationuncertainty. In general, the measurement can be tailored toprovide the lev
