1、Designation: C1514 08 (Reapproved 2017)Standard Test Method forMeasurement of235U Fraction Using Enrichment MeterPrinciple1This standard is issued under the fixed designation C1514; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he 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 covers the quantitative determinationof the fraction of235U in uranium using measurement o
3、f the185.7 keV gamma-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
4、 for the entire 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
5、 listed in Annex 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,operations, and equipment. This standard does not purport toaddress all of the safety concerns, if any, as
6、sociated with 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:2C1030 Test Method for Determination of Plutonium Isotopic
7、Composition by Gamma-Ray SpectrometryC1490 Guide for the Selection, Training and Qualification ofNondestructive Assay (NDA) PersonnelC1592 Guide for Nondestructive Assay MeasurementsC26.10 Terminology Guide2.2 ANSI Standard:N42.14 Calibration and Use of Germanium Spectrometersfor the Measurement of
8、Gamma-Ray 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 th
9、at emission 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
10、thecalibration 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 factormu
11、st be applied.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 me
12、thod relies 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.1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct resp
13、onsibility of Subcommittee C26.10 on NonDestructive Assay.Current edition approved Jan. 1, 2017. Published January 2017. Originallyapproved in 2002. Last previous edition approved in 2008 as C1514 08. DOI:10.1520/C1514-08R17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcon
14、tact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright
15、 ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International
16、Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.15.3 Use of a low resolution detector (for example, NaIdetector) to measure uranium with235U fraction approximately10 % which is contained in a thin-walled container can providea
17、rapid (typically 100 s), easily portable measurement 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 wh
18、en measuring uranium with235U fractionin the range 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, a
19、nd the uranium-bearing material within the itemmust 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 ch
20、emical composition.5.7 When measuring items, using 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 uraniu
21、m, or high-resolutionmeasurements should be performed.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 e
22、ffect can resultin significant biases.6.2 Incorrect 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 de
23、ad timecan usually be eliminated by modifications to 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 dist
24、ributed and well characterized. The pres-ence of impurities, 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 ofi
25、nterference is most often encountered in low-resolutionmeasurement, 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 an
26、d the HPGe measurement methods.7. Apparatus7.1 Gamma-Ray Detector SystemGeneral guidelines forselection of detectors and signal-processing electronics arediscussed in Guide C1592, Test Method C1030, and ANSIstandard N42.14. Refer to the References section for a list ofother recommended references (1
27、).4This system typicallyconsists of a gamma-ray detector, spectroscopy gradeamplifier, high-voltage bias supply, multi-channel analyzer,and detector collimator. The system may also include detectorbackshielding, an ultrasonic thickness gauge, an oscilloscope, aspectrum stabilizer, a computer, and a
28、printer.7.2 A high-resolution detector system 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 generall
29、y larger,heavier, and more costly than low-resolution 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 syste
30、ms, and elimi-nate some interferences.7.2.1 High-Resolution DetectorA high-resolution detectorwith 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 wit
31、h high (15 %) efficiency is used.The selected 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 fol
32、lowing specifications is recommended: a 5-cmdiam, 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-ray
33、sincident upon it. The detector collimator must also block inexcess of 99.9 % of the gamma-rays incident upon it and the4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.TABLE 1 Interfering Gamma-RaysIsotope ParentGamma-Ray Energy(keV)Measurement Affecte
34、d226Ra 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 ResolutionC1514 08 (2017)2aperture must restrict the field of vi
35、ew 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 fabricated from cadmium or tin)may, optionally, be included to reduce the intensity of gamma-induced X rays from the coll
36、imator and shield assembly.7.3 Preparation of Apparatus: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, assem
37、bling, and disassembling these systems.8.2 Collimators and shielding may use materials (forexample, 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 pres
38、ent both chemical andradiological hazards. The analyst 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 material
39、s. Containers inthe same configuration as the items 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.
40、2 Secondary reference materials can be fabricated 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
41、 material for a sufficient amountof time to obtain 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 ofurani
42、um-bearing material contained in the item, the countingtime 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 b
43、e determined using peak fitting or regions of interest.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)
44、isrecommended for calibration of high-resolution 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 enr
45、ich-ments for items to be measured. Use of the method 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
46、 Annex A2,asapplicable to the method chosen for peak area determination.10. Procedure10.1 Good measurement practice includes the measurementof an item used as a control source (refer to Guide C1592).10.2 The uranium-bearing material within the measureditem must completely fill the field of view of t
47、he collimateddetector in the geometry used for calibration.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
48、was used for calibration (peak fittingor regions 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 con
49、tained in theitem, the counting time used, the net 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 appropriate corrections to account for differentchemical forms verses that used during calibration. See Refer-ences (2) and (3).10.10 Compute the enrichment and the measurement uncer-tainty using equations shown in Annex A1 or Annex A
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