1、Designation: C 1133 03Standard Test Method forNondestructive Assay of Special Nuclear Material in Low-Density Scrap and Waste by Segmented Passive Gamma-Ray Scanning1This standard is issued under the fixed designation C 1133; the number immediately following the designation indicates the year oforig
2、inal adoption 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 transmission-corrected non-destruc
3、tive assay (NDA) of gamma-ray emitting specialnuclear materials (SNMs), most commonly235U,239Pu,and241Am, in low-density scrap or waste, packaged in cylin-drical containers. The method can also be applied to NDA ofother gamma-emitting nuclides including fission products.High-resolution gamma-ray spe
4、ctroscopy is used to detect andmeasure the nuclides of interest and to measure and correct forgamma-ray attenuation in a series of horizontal segments(collimated gamma detector views) of the container. Correc-tions are also made for counting losses occasioned by signalprocessing limitations (1-3).21
5、.2 There are currently several systems in use or underdevelopment for determining the attenuation corrections forNDA of radioisotopic materials (4-8). A related technique,tomographic gamma-ray scanning (TGS), is not included inthis test method (9,10).1.2.1 This test method will cover two implementat
6、ions ofthe Segmented Gamma Scanning (SGS) procedure: (1) IsotopeSpecific (Mass) Calibration, the original SGS procedure, usesstandards of known radionuclide masses to determine detectorresponse in a mass versus corrected count rate calibration thatapplies only to those specific radionuclides for whi
7、ch it iscalibrated, and (2) Efficiency Curve Calibration, an alternativemethod, typically uses non-SNM radionuclide sources todetermine system detection efficiency vs. gamma energy andthereby calibrate for all gamma-emitting radionuclides ofinterest (11). These two methods will be covered in detail
8、in theremainder of the main body of this test method and Annex A1.1.2.1.1 Efficiency Curve Calibration, over the energy rangefor which the efficiency is defined, has the advantage ofproviding calibration for many gamma-emitting nuclide forwhich half-life and gamma emission intensity data are avail-a
9、ble.1.3 The assay technique may be applicable to loadings up toseveral hundred grams of nuclide in a 208-L (55-gal) drum,with more restricted ranges to be applicable depending onspecific packaging and counting equipment considerations.1.4 Measured transmission values must be available for usein calc
10、ulation of segment-specific attenuation corrections at theenergies of analysis.1.5 A related method, SGS with calculated correction fac-tors based on sample content and density, is not included in thisstandard.1.6 The values stated in SI units are to be regarded as thestandard. The values given in p
11、arentheses are for informationonly.1.7 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 and health practices and determine the applica-bility of regulatory limit
12、ations prior to use. Specific precau-tionary statements are given in Section 8.2. Referenced Documents2.1 ASTM Standards:C 982 Guide for Selecting Components for Energy-Dispersive X-Ray Fluorescence (XRF) Systems3C 1030 Test Method for Determination of Plutonium Isoto-pic Composition by Gamma Ray Sp
13、ectrometry3C 1128 Guide for Preparation of Working Reference Mate-rials for Use in the Analysis of Nuclear Fuel CycleMaterials3C 1156 Guide for Establishing Calibration for a Measure-ment Method Used to Analyze Nuclear Fuel Cycle Mate-rials3C 1207 Test Method for Nondestructive Assay of Plutoniumin
14、Scrap and Waste by Passive Neutron CoincidenceCounting3C 1210 Guide for Establishing a Measurement SystemQuality Control Program for Analytical Chemistry Labo-ratories within the Nuclear Industry3C 1458 Test Method for Nondestructive Assay of Pluto-nium, Tritium and241Am by Calorimetric Assay31This
15、test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on Nondestruc-tive Assay.Current edition approved July 10, 2003. Published September 2003. Originallyapproved in 1996. Last previous edition approved in 1996 as C
16、1133 96.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3Annual Book of ASTM Standards, Vol 12.01.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E 181 Test Methods for Detector Cali
17、bration and Analysisof Radionuclides42.2 ANSI Standards:5ANSI/IEEE 325 Test Procedures for Germanium Gamma-Ray DetectorsANSI N42.14 Calibration and Use of Germanium Spec-trometers for the Measurement of Gamma-Ray EmissionRates of Radionuclides2.3 NRC Regulatory Guides:6Regulatory Guide 5.9, Rev. 2,
18、Guidelines for GermaniumSpectroscopy Systems for Measurement of SpecialNuclear MaterialsRegulatory Guide 5.11, Rev. 1, Nondestructive Assay ofSpecial Nuclear Material Contained in Scrap and WasteRegulatory Guide 5.53, Rev. 1, Qualification, Calibration,and Error Estimation Methods for Nondestructive
19、 Assay3. Summary of Test Method3.1 The assay of the nuclides of interest is accomplished bymeasuring the intensity of one or more characteristic gammarays from each nuclide. Corrections are made for countrate-related losses and attenuation by the item. The appropriatemass or efficiency calibration t
20、hen provides the relationshipbetween observed gamma-ray intensity and nuclide content.3.2 Either of two distinct calibration methods can be used:3.2.1 Isotope Specific Calibration provides assay results foronly those radionuclides for which the SGS is specificallycalibrated. Calibration is performed
21、 using standards containingthe radionuclides to be assayed.3.2.2 Effciency Curve Calibration entails determination ofthe system detecton efficiency as a function of gamma rayenergy. Analysis of assay data consists of using the energy ofa peak to infer the emitting radionuclide, and then calculatingt
22、he radionuclide mass from the specific activity and the gammaemission intensity of the radionuclide, and the corrected countrate and detector efficiency at the peak energy.3.3 The assay item is rotated about its vertical axis andscanned segment by segment along that axis, thereby reducingthe effects
23、 of nonuniformity in both matrix density and nuclidedistribution (see Fig. 1).3.4 Count rate-dependent losses from pulse pile-up andanalyzer dead time are corrected for by electronic modules, aradioactive source, a pulser, or a combination of these.3.5 The average linear attenuation coefficient of e
24、ach hori-zontal segment is calculated by measurement of the transmittedintensity of an appropriate external gamma-ray source. Thesource is mounted directly opposite the gamma-ray detector, onthe far side of the assay item (see Fig. 1).3.6 Two conditions must be met to optimize SGS assayresults as fo
25、llows:3.6.1 The particles containing the nuclides of interest mustbe small enough to minimize self-absorption of emitted gammaradiation (12).3.6.1.1 Under specific conditions, particles large enough toprovide significant self absorption (lumps ) may be assayedaccurately. These conditions include use
26、 of specific Nuclidedifferential peak calibration and calibration using mass stan-dards that have the same attenuation characteristics over theenergy range used for quantitative measurements as the mate-rials to be assayed.3.6.1.2 An alternative approach to mass calibration withstandards that contai
27、n the same sized particles is to applycorrection algorithms that are based on the differential responseof two or more peaks at different energies from the samenuclide. For example, the 129 and 414 keV peaks of239Pu orthe 144 and 186 keV peaks of235U could be used (see 6.7).3.6.1.3 The presence of lu
28、mps in material being assayedalso can be detected using differential peak response algori-hms.3.6.2 The mixture of material within each item segmentmust be sufficiently uniform to apply an attenuation correctionfactor, generally computed from a measurement of gamma-raytransmission through the segmen
29、t.3.7 The corrected gamma-ray count rates for the nuclides ofinterest are determined on a segment-by-segment basis. Theprecision of the measured count rate of each gamma ray usedfor analysis is also estimated on a segment-by-segment basis.At the completion of the measurement of all segments,correcte
30、d count rates are summed, and mass values for thenuclides of interest in the entire container are calculated basedeither on comparisons to appropriate calibration materials orfrom the gamma emission rates determined from the segmentefficiencies determined over the energy range of interest. Basedon c
31、ounting statistics for individual segments, precision valuesare propagated to obtain the estimated precision of the analysis.3.8 In the event that a single nuclide of an element ismeasured and the total element mass is required (for4Annual Book of ASTM Standards, Vol 12.02.5Available from American N
32、ational Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.6Available from U.S. Nuclear Regulatory Commission, Public Document Room,1717 H St., N.W., Washington, DC 20555.FIG. 1 Typical Arrangement for Segmented Gamma-Ray ScanningC1133032example,239Pu and total plutonium), it i
33、s common practice toapply a known or estimated nuclide/total element ratio to thenuclide assay value to determine the total element content.3.8.1 Isotope ratios can be determined using gamma isoto-pic analysis techniques such as those described in Test MethodC 1030.4. Significance and Use4.1 Segment
34、ed gamma-ray scanning provides a nondestruc-tive means of measuring the nuclide content of scrap and wastewhere the specific nature of the matrix and the chemical formand relationship between the nuclide and matrix may beunknown.4.2 The procedure can serve as a diagnostic tool thatprovides a vertica
35、l profile of transmission and nuclide concen-tration within the item.4.3 Sample preparation is generally limited to good waste/scrap segregation practices that produce relatively homoge-neous items that are required for any successful waste/inventory management and assay scheme, regardless of themea
36、surement method used. Also, process knowledge should beused, when available, as part of a waste management programto complement information on sample parameters, containerproperties, and the appropriateness of calibration factors.5. Interferences5.1 Radionuclides may be present in the assay item tha
37、tproduce gamma rays with energies that are the same or verynearly the same as the gamma rays suggested for nuclide ortransmission measurement. The areas of the closely spacedpeaks that are produced in the gamma-ray spectrum cannot becalculated by simple spectroscopic procedures. Peak fittingsoftware
38、 routines may be able to resolve closely spaced peaksin some cases; if not, the nuclide of interest may produce othergamma rays that may be used for analysis.5.1.1 The peak produced by the 661.6-keV gamma ray from137Cs would interfere with calculation of the area of the241Am peak produced by its 662
39、.4-keV gamma ray. The721.9-keV gamma ray of241Am may be a useful alternative.5.1.2 The peak produced by the 765.8-keV gamma ray from95Nb would interfere with calculation of the area of the238Pupeak produced by its 766.4-keV gamma ray. The 786.3-keVgamma ray of238Pu may be a useful alternative.5.1.3
40、Occasionally,237Np is found in the presence of pluto-nium. The237Np daughter,233Pa, emits a gamma ray at 415.8-keV along with several gamma rays in the range from 300 to400 keV. Peaks from these gamma rays would interfere withcalculation of the area of the239Pu peak produced by its413.7-keV gamma ra
41、y and several other often used peaksfrom239Pu. In this case, the peak produced by the 129.3-keVgamma ray of239Pu may be the only reasonable alternative.5.1.4 The peak produced by the 63.1-keV gamma rayfrom169Yb, sometimes used as the transmission sourcefor235U assays, may interfere with calculation
42、of the area ofthe peak produced by the 59.5-keV gamma ray of241Am,which is used as the count rate correction source. The169Ybgamma ray can be sufficiently attenuated by placing a cadmiumabsorber over the transmission source or the problem can beavoided altogether by using a two-pass assay. The first
43、 mea-surement pass measures the intensity of the transmissionsource for each segment. The second measurement passmeasures the intensity of the 413.7-keV239Pu gamma-rayemission from each segment with the transmission sourceshutter closed.5.1.5 Transmission source peaks may have errors intro-duced by
44、the presence of a radionuclide in the assay materialthat emits gamma rays at or near one or more of the measuredtransmission energies. The affected measurements will then behigher than the actual transmissions through the item, leadingto calculation of a lower than actual correction factor andquanti
45、ty of measured radionuclide.5.2 In the case of239Pu assays using75Se as a transmissionsource, random coincident summing of the 136.00 and 279.53-keV gamma-ray emissions from75Se produces a low-intensitypeak at 415.5-keV that interferes with calculation of the area ofthe239Pu peak produced by its 413
46、.7-keV gamma ray. Theeffects of this sum-peak can be reduced by attenuating theradiation from the transmission source to the lowest intensityrequired for transmission measurements of acceptable preci-sion. This problem also can be avoided by making a two-passassay.5.3 Peaks may appear at the gamma-r
47、ay energies used foranalysis when there is no nuclide present on the turntable. Thelikely cause is excessive amounts of nuclide stored in thevicinity of the detector. The preferred solution to this problemis removal of the nuclide from the vicinity and restraint ofnuclide movements around the system
48、 during measurements. Ifthese conditions cannot be met, sufficient shielding must beprovided to eliminate these peaks. Shielding opposite thedetector, on the far side of the item to be assayed, will also helpto reduce the amount of ambient radiation seen by the detector(see Fig. 1).6. Sources of Err
49、or6.1 Sources of error specifically applicable to segmentedgamma-ray scanning are discussed in this section. Generaldescriptions of sources of error encountered in gamma-raynondestructive assay systems can be found in NRC RegulatoryGuide 5.11.6.2 The bias in an assay is strongly dependent on how wellthe attenuation for each segment has been determined. In orderto determine the attenuation, a radioactive source with agamma ray of nearly the same energy as the gamma ray of thenuclide of interest is positioned directly opposite the gamma-ray detector, on the far side of the assay item (se
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