1、Designation: C1207 10Standard Test Method forNondestructive Assay of Plutonium in Scrap and Waste byPassive Neutron Coincidence Counting1This standard is issued under the fixed designation C1207; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the 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 describes the nondestructive assay ofscrap or waste for plutonium content us
3、ing passive thermal-neutron coincidence counting. This test method provides rapidresults and can be applied to a variety of carefully sortedmaterials in containers as large as several thousand liters involume. The test method applies to measurements of238Pu,240Pu, and242Pu and has been used to assay
4、 items whose totalplutonium content ranges from 10 mg to 6 kg (1).21.2 This test method requires knowledge of the relativeabundances of the Pu isotopes to determine the total Pu mass(Test Method C1030).1.3 This test method may not be applicable to the assay ofscrap or waste containing other spontane
5、ously fissioning nu-clides.1.3.1 This test method may give biased results for measure-ments of containers that include large amounts of hydrogenousmaterials.1.3.2 The techniques described in this test method havebeen applied to materials other than scrap and waste (2, 3).1.4 This test method assumes
6、 the use of shift-register-basedcoincidence technology (4).1.5 Several other techniques that are often encountered inassociation with passive neutron coincidence counting existThese include neutron multiplicity counting (5, 6, Test MethodC1500), add-a-source analysis for matrix correction (7), fluxp
7、robes also for matrix compensation, cosmic-ray rejection (8)to improve precision close to the detection limit, and alterna-tive data collection electronics such as list mode data acquisi-tion. Passive neutron coincidence counting may also be com-bined with certain active interrogation schemes as in
8、TestMethods C1316 and C1493. Discussions of these establishedtechniques are not included in this method.1.6 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
9、health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C986 Guide for Developing Training Programs in theNuclear Fuel CycleC1009 Guide for Establishing a QualityAssurance Programfor Analytical Chemistry Laboratories Within
10、the NuclearIndustryC1030 Test Method for Determination of Plutonium Isoto-pic Composition by Gamma-Ray SpectrometryC1068 Guide for Qualification of Measurement Methods bya Laboratory Within the Nuclear IndustryC1128 Guide for Preparation of Working Reference Mate-rials for Use in Analysis of Nuclear
11、 Fuel Cycle MaterialsC1133 Test Method for Nondestructive Assay of SpecialNuclear Material in Low-Density Scrap and Waste bySegmented Passive Gamma-Ray ScanningC1210 Guide for Establishing a Measurement System Qual-ity Control Program forAnalytical Chemistry LaboratoriesWithin the Nuclear IndustryC1
12、316 Test Method for Nondestructive Assay of NuclearMaterial in Scrap and Waste by Passive-Active NeutronCounting Using252Cf ShufflerC1458 Test Method for NondestructiveAssay of Plutonium,Tritium and241Am by Calorimetric AssayC1490 Guide for the Selection, Training and Qualificationof Nondestructive
13、Assay (NDA) PersonnelC1493 Test Method for Non-Destructive Assay of NuclearMaterial in Waste by Passive andActive Neutron CountingUsing a Differential Die-Away SystemC1500 Test Method for Nondestructive Assay of Plutoniumby Passive Neutron Multiplicity CountingC1592 Guide for Nondestructive Assay Me
14、asurementsC1673 Terminology of C26.10 NondestructiveAssay Meth-ods1This practice is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on NonDestructive Assay.Current edition approved June 1, 2010. Published July 2010. Originally
15、 approvedin 1991. Last previous edition approved in 2003 as C1207 03. DOI: 10.1520/C1207-10.2The boldface numbers in parentheses refer to the list of references at the end ofthis test method.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serv
16、iceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.2 ANSI Standards:4ANSI 15.20 Guide to Calibrating Non
17、destructive AssaySystemsANSI 15.36 Nondestructive Assay Measurement Controland Assurance3. Terminology3.1 Refer to Terminology C1673 for definitions used in thistest method.4. Summary of Test Method4.1 The even mass isotopes of Pu fission spontaneously. Onthe average, two or more prompt neutrons are
18、 emitted perfission event. The number of time correlated or coincidentneutrons detected by the instrument is related to the effectivemass of240Pu, meff, present in the time. The effective240Pumass is a weighted sum of the even mass isotopes of Pu in theassay item. The total Pu mass is determined fro
19、m the knownplutonium isotopic ratios and the measured quantity meff.4.2 The shift register technology is intended to correct forthe effects of Accidental neutron coincidences which resultfrom the registration of neutrons in the coincidence gate whichare not correlated in time to the neutron which tr
20、iggered theinspection of the gate.4.3 Other factors which may affect the assay are neutron selfmultiplication, matrix components with large (a, n) reactionrates, neutron absorbers, or moderators. Corrections for theseeffects are often not possible from the measurement data alone,consequently assay i
21、tems are commonly sorted into materialcategories or additional information is sometimes used.4.4 Corrections are typically made for electronic deadtimeand neutron background.4.5 Calibrations are typically based on measurements ofwell documented and appropriate reference materials. Model-ing based on
22、 knowledge of the instrument design and thephysical principles of neutron interactions may also be applied.4.6 This method includes measurement control tests toverify reliable and stable performance of the instrument.5. Significance and Use5.1 This test method is useful for determining the plutonium
23、content of scrap and waste in containers ranging from smallcans with volumes of the order of a mL to crates and boxes ofseveral thousand liters in volume. A common applicationwould be to 208-L (55-gal) drums. Total Pu content rangesfrom 10 mg to 6 kg (1). The upper limit may be restricteddepending o
24、n specific matrix, calibration material, criticalitysafety, or counting equipment considerations.5.2 This test method is applicable for U.S. Department ofEnergy shipper/receiver confirmatory measurements (9),nuclear material diversion detection, and International AtomicEnergy Agency attributes measu
25、rements (10).5.3 This test method should be used in conjunction with ascrap and waste management plan that segregates scrap andwaste assay items into material categories according to some orall of the following criteria: bulk density, the chemical forms ofthe plutonium and the matrix, americium to p
26、lutonium isotopicratio, and hydrogen content. Packaging for each categoryshould be uniform with respect to size, shape, and compositionof the container. Each material category might require calibra-tion standards and may have different Pu mass limits.5.4 Bias in passive neutron coincidence measureme
27、nts isrelated to item size and density, the homogeneity and compo-sition of the matrix, and the quantity and distribution of thenuclear material. The precision of the measurement results isrelated to the quantity of nuclear material, the (a,n) reactionrate, and the count time of the measurement.5.4.
28、1 For both benign matrix and matrix specific measure-ments, the method assumes the calibration reference materialsmatch the items to be measured with respect to the homoge-neity and composition of the matrix, the neutron moderator andabsorber content, and the quantity of nuclear material, to theexte
29、nt they affect the measurement.5.4.2 Measurements of smaller containers containing scrapand waste are generally more accurate than measurements oflarger items.5.4.3 It is recommended that where feasible measurementsbe made on items with homogeneous contents. Heterogeneityin the distribution of nucle
30、ar material, neutron moderators, andneutron absorbers have the potential to cause biased results.5.5 The coincident neutron production rates measured bythis test method are related to the mass of the even numberisotopes of plutonium. If the relative abundances of theseisotopes are not accurately kno
31、wn, biases in the total Pu assayvalue will result.5.6 Typical count times are in the range of 300 to 3600 s.5.7 Reliable results from the application of this methodrequire training of the personnel who package the scrap andwaste prior to measurement and of personnel who perform themeasurements. Trai
32、ning guidance is available fromANSI 15.20, Guides C986, C1009, C1068, and C1490.6. Interferences6.1 Conditions affecting measurement uncertainty includeneutron background, moderators, multiplication, (a, n) rate,absorbers, matrix and nuclear material heterogeneity, and othersources of coincident neu
33、trons. It is usually not possible todetect these problems or to calculate corrections for theseeffects from the measurement data alone. Consequently, assayitems are sorted into material categories defined on the basis ofthese effects.6.2 Neutron background levels from external sources shouldbe kept
34、as low and as constant as practical. Corrections can bemade for the effects of high-neutron background levels, butthese will adversely affect measurement precision and detec-tion limits.6.3 Neutron moderation by low atomic mass materials willnot only increase thermal-neutron absorption effects, but
35、willalso increase multiplication effects. Consequently, the mea-sured neutron rates may be either smaller or larger than thosefor a nonmoderating matrix. Hydrogenous matrices contributethe most to this effect (11).6.4 Both spontaneous and induced fissions produce coinci-dent neutrons. The instrument
36、, however, cannot distinguish4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.C1207 102between them. Three factors that strongly affect the degree ofmultiplication are the mass of fissile material, its density, andits geom
37、etry. Increases in mass that are not accompanied bychanges in either density or geometry will result in predictablemultiplication increases that can be incorporated into thecalibration function. Localized increases in nuclear materialdensity and/or changes in the geometry are likely to causeunknown
38、changes in multiplication and measurement bias.6.5 Neutrons from (a, n) reactions are an interference biassource if they induce multiplication effects. In addition, (a,n)neutrons can increase the Accidentals rate thereby affecting thestatistical precision of the assay which is based on the netcoinci
39、dence rate.6.6 Biases may result from non-uniformity in the sourcedistribution and heterogeneity in the matrix distribution.6.7 Other spontaneous fission nuclides (for example, curiumor californium) will increase the coincident neutron countrates, causing an overestimation of the plutonium content.6
40、.8 Cosmic rays, which are difficult to shield against, canproduce coincident neutrons. Cosmic ray effects become largerfor small quantities of Pu in the presence of large quantities ofrelatively high atomic number materials, for example, iron orlead are more prolific producers than celluloxic wastes
41、 (see12.5).7. Apparatus7.1 Counting AssemblySee Fig. 1.7.1.1 The apparatus used in this test method can be obtainedcommercially. Specific applications may require customizeddesign. The neutron detectors are usually3He proportionalcounters embedded in polyethylene. The detection efficiencyfor neutron
42、s of fission energy is typically at least 15 %. Largerdetection efficiencies provide better precision and lower detec-tion limits for a given count time. A short dieaway time is alsoimportant in that it allows a shorter gate width to be used whichin turn helps control the Accidents. Ideally, the cou
43、nterdetection efficiency should vary less than 10 % over the itemvolume. The coincident response varies as the square of thedetection efficiency.7.1.2 Reproducible positioning of the item in the assaychamber is important for obtaining the best accuracy. Thiscounting geometry should be maintained for
44、 the measurementof all reference materials and assay items. (See 11.7.)7.1.3 A 0.4 mm to 1mm thick cadmium liner (12) is ofteninstalled on the inside surfaces of the counting chambersurrounding the assay item. This liner will reduce the dieawaytime, decrease multiplication inside the item from retur
45、ningneutrons and decrease the effects on the assay of neutronabsorbers inside the item. The liner will also decrease neutrondetection efficiency due to absorption of thermalized neutronsand may increase the cosmic ray spallation background. Thefinal design may represent a compromise between multiple
46、conflicting influences.7.2 ShieldingThe detector assembly is often surroundedby cadmium and an additional layer of hydrogenous material(see Fig. 1). Approximately 100 mm of polyethylene canreduce the neutron background in the assay chamber byapproximately a factor of 10 (13).7.3 ElectronicsHigh-coun
47、t-rate nuclear electronics pro-vide a standard logic pulse from the3He proportional counters.These pulses are processed by the shift-register coincidencetechnology.7.4 Data acquisition and reduction can be facilitated byinterfacing the instrument to a computer.8. Hazards8.1 Safety HazardsConsult qua
48、lified professionals asneeded.8.1.1 Precautions should be taken to prevent inhalation,ingestion, or the spread of Pu contamination during waste orscrap handling operations. All containers should be surveyedon a regular basis with an appropriate monitoring device toverify their continued integrity.8.
49、1.2 Precautions should be taken to minimize personnelexposure to radiation.8.1.3 Precautions should be taken regarding nuclear critical-ity, especially of unknown items. The measurement chamberapproximates a reflecting geometry for fast neutrons. Theassumption that waste is not of criticality concern is notrecommended.8.1.4 Counting chambers may contain a cadmium liner.Precautions should be taken to prevent the inhalation oringestion of cadmium. It is a heavy metal poison. Cadmiumshielding should be covered with nontoxic materials.8.1.5 Precautions should be taken to avoid cont
