1、Designation: C 1514 02Standard Test Method forMeasurement of235U Fraction using the 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 l
2、ast 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 quantitative determinationof the fraction of235U in uranium using measurement of the185.7
3、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 for the en
4、tire range of235Ufraction, from depleted (0.2 %235U) to very highly 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 Appendix B.1.5
5、 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 itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine th
6、e applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:C 982 Standard Guide for Selecting Components forEnergy-Dispersive X-Ray Fluorescence (XRF) Systems3. Terminology3.1 Infinite thicknessThe thickness of a material which isat least seven mean free paths f
7、or 185.7 keV gamma rays (i.e.,the minimum thickness which will attenuate 99.9 % of 185.7keV gamma rays incident on the compound).3.2 EnrichmentThe fraction of235U relative to total ura-nium in an item, typically expressed as a weight percentage.3.3 Atom PercentThe ratio of the number of atoms of agi
8、ven isotope (e.g.,235U) to the total number of atoms of anelement (e.g., uranium), expressed as a percentage.3.4 Weight PercentThe ratio of the weight of a givenisotope (e.g.,235U) to the total weight of an element (e.g.,uranium), expressed as a percentage.4. Summary of Test Method4.1 The test metho
9、d consists of measuring the emission rateof 185.7 keV gamma rays from an item and correlating thatemission rate with the enrichment of the uranium contained inthe item.4.2 Calibration is achieved using reference materials ofknown enrichment. Corrections are made for attenuating ma-terials present be
10、tween the uranium-bearing material and thedetector and for chemical compounds different from 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
11、 respect to the 185.7 keVgamma ray.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 sampl
12、ing error.5.2 Use of a low resolution detector (e.g., NaI detector) tomeasure uranium with235U fraction approximately 10 %which is contained in a thin-walled container can provide arapid (typically 100 s), easily portable measurement systemwith precision of 0.6 % and bias of less than 1 %.5.3 Use of
13、 a high resolution detector (e.g., high-puritygermanium) can provide measurement with a precision betterthan 0.2 % and a bias less than 1 % within a 300-sec measure-ment time when measuring uranium with235U fraction in therange of 0.711 % to 4.46 % which is contained in thin-walledcontainers.5.4 In
14、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 be infinitely thick with respect to the 185.7 keV gammaray.5.5 Items m
15、ust be homogeneous with respect to both235Ufraction and chemical composition.5.6 The uranium-bearing materials in the measured items1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on NonDestructive Assay.C
16、urrent edition approved Jan. 10, 2002. Published May 2002.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.and calibration reference materials used for calibration must fillthe detector field of view.5.7 When measuring items, using lo
17、w-resolution detectors,in thin-walled containers that have not reached secular equi-librium, either the method should not be used, additionalcorrections should be made to account for the age of theuranium, or high-resolution measurements should be per-formed.5.8 The method is typically used as a ver
18、ification technique,not to establish enrichment.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 knowledge of chemical
19、 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 to the detectorcollimat
20、or 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 impurities, at concentra
21、tions which can measurablyattenuate the 185.7 keV gamma ray and which are notaccounted 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-resolution mea-surement, but c
22、an affect high-resolution measurements.7. ApparatusGamma-Ray Detector System. General guidelines for selec-tion of detectors and signal-processing electronics are dis-cussed in Guide C 982 and NRC Regulatory Guide 5.9, Rev. 2(1). This system typically consists of a gamma-ray detector,spectroscopy gr
23、ade amplifier, high-voltage bias supply, multi-channel analyzer, and detector collimator. The system may alsoinclude detector backshielding, an ultrasonic thickness gauge,an oscilloscope, a spectrum stabilizer, a computer, and aprinter.7.1 A high-resolution detector system or a low-resolutiondetecto
24、r system should be selected, depending on precision andbias requirements for the measurements. Additional detectorselection considerations are measurement time, cost, and easeof use. Because they are cooled using liquid nitrogen, high-resolution detector systems are larger, heavier, and somewhatmore
25、 difficult to use than low-resolution detector systems. Inaddition, 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-na
26、te some interferences.7.1.1 High-resolution detector. A high-resolution detectorwith a resolution of 2000 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 %)
27、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.7.1.2 Low-resolution detector. A low-resolution detectorwith the following speci
28、fications is recommended: a 5-cmdiam, 1.25-cm thick or larger detector with a resolution of15 % or better at 122 keV.7.1.3 Other system components. Specifications for ampli-fier, high-voltage bias supply, multi-channel analyzer, andother components of the system are provided in C 982.7.1.4 Collimato
29、r and Shield Assembly. The 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 must also block inexcess of 99.9 % of the gamma rays incident upon it and theaperture must restrict
30、 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 fabricated from cadmium or tin)may, optionally, be included to reduce the intensity of gamma-induced X ra
31、ys from the collimator and shield assembly.7.2 Preparation of Apparatus7.2.1 Pole zero. Prior to the use of the detector system, thepole zero should be adjusted per manufacturers instructions.7.2.2 Gain. After setting the pole zero, set the gain so thatthe 185.7 keV peak is well within the observabl
32、e spectrum.Depending on the software used for analysis, peak positionmay not be arbitrary.7.2.3 Other parameters. Other detection parameters (e.g.,threshold, zero level) should be configured as described inC 982.8. Hazards8.1 Gamma-ray detectors may use power-supply voltages ashigh as 5 kV. Appropri
33、ate precautions should be taken whenusing, assembling, and disassembling these systems.8.2 Collimators and shielding may use materials (e.g., leadand cadmium) which are considered hazardous and/or toxicand can be physically heavy and difficult to maneuver. Propercare in their use and disposal are re
34、quired.8.3 Uranium-bearing materials present both chemical andradiological hazards. The analyst should be aware of thesehazards and take appropriate precautions.TABLE 1 Interfering Gamma RaysIsotope Parent Gamma-Ray Energy (keV) Measurement Affected226Ra N/A 185.9 High Resolution, LowResolution212Pb
35、232U 238.6 Low Resolution224Ra232U 241.0 Low Resolution233Pa237Np 300.1 Low Resolution233Pa237Np 311.9 Low Resolution234Th238U Bremsstrahlung Low Resolution99Tc N/A Bremsstrahlung Low ResolutionC 151429. Calibration9.1 Two types of reference materials are typically used forperforming calibration mea
36、surements (1) certified referencematerials, and (2) reference materials. Certified referencematerials are preferred for calibration of high resolutionmeasurement systems. Containers in the same configuration asthe items to be measured are preferred for low resolutionmeasurements.9.1.1 Certified refe
37、rence materials are available which havebeen fabricated for the primary purpose of calibration ofgamma-ray systems for enrichment measurements using theenrichment meter principle. These materials are available inthe range of235U fraction from 0.31 % to 4.46 %. Highresolution measurement systems are
38、typically calibrated usingthese reference materials.9.1.2 Secondary reference materials can be fabricated byanalyzing for enrichment using destructive analysis techniqueswhich have been calibrated with NIST traceable referencematerials. Low-resolution measurement systems are typicallycalibrated usin
39、g these secondary reference materials.9.2 Place the container to be used for calibration in contactwith the detector collimator, with the uranium in the referencematerial filling the detector field of view.9.3 Measure the reference material for a sufficient amountof time to obtain the desired precis
40、ion 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 countingtime used, the
41、 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 interest.If regions of
42、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 systems. Themeasurem
43、ent 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 method outside therang
44、e within which it was calibrated is possible, but is notrecommended.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 peak area determination.10. Procedure10.1 Measurement Control. Prior to the measure
45、ment ofunknown items, local measurement control procedures shouldbe followed. Good measurement practice includes, at a mini-mum, the measurement of an item used as a control source atthe start and end of each day of measurements. The source canbe a calibration reference material or an item which ism
46、aintained in inventory for the purpose of measurementcontrol, and does not change. The results of these measure-ments should be evaluated each day of measurement, using avalid statistical technique (e.g., control charting) to assesscontrol.10.2 Place the detector collimator in contact with thecontai
47、ner of the item to be measured, with the item in front ofthe detector. The uranium-bearing material within the mea-sured item must completely fill the field of view of the detector.10.3 Measure the item for a sufficient amount of time toobtain the desired precision for the net peak area. The precisi
48、onfor the net peak area should be smaller than the target overallmeasurement system uncertainty.10.4 Obtain the wall thickness and material type of theitems container.10.5 Record the identifier for the measured item, the type ofuranium-bearing material contained in the item, the countingtime used, t
49、he 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 must be determined using the same method as was usedfor calibration (peak fitting or regions of interest).10.6 Compute the attenuation correction factor and itsuncertainty using equations shown in Annex A1.10.7 Compute the enrichment and the measurement uncer-tainty using equations shown in Annex A1 or Annex A2, asappropriate.11. Precision and BiasPrecision an
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