1、Designation: C 1207 03Standard Test Method forNondestructive Assay of Plutonium in Scrap and Waste byPassive Neutron Coincidence Counting1This standard is issued under the fixed designation C 1207; the number immediately following the designation indicates the year oforiginal adoption or, in the cas
2、e 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 describes the nondestructive assay ofscrap or waste for plutonium content
3、 using 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 208-L drums. The testmethod applies to measurements of238Pu,240Pu, and242Pu andhas been used to assay items whose total p
4、lutonium contentranges from 0.01 to 6000 g (1).21.2 This test method requires knowledge of the relativeabundances of the plutonium isotopes to determine the totalplutonium mass.1.3 This test method may not be applicable to the assay ofscrap or waste containing other spontaneously fissioning nu-clide
5、s.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 the use of shift-registe
6、r-basedcoincidence technology (4).1.5 Several other techniques that are related to passiveneutron coincidence counting exist These include neutronmultiplicity counting (5,6), add-a-source analysis (7), andcosmic-ray rejection (8). Discussions of these techniques arenot included in this method.1.6 Th
7、is 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 limitations prior to use.2. Referenced Documen
8、ts2.1 ASTM Standards:C 859 Terminology Relating to Nuclear Materials3C 986 Guide for Developing Training Programs in theNuclear Fuel Cycle3C 1009 Guide for Establishing a Quality Assurance Pro-gram for Analytical Chemistry Laboratories Within theNuclear Industry3C 1030 Test Method for Determination
9、of Plutonium Isoto-pic Composition by Gamma-Ray Spectrometry3C 1068 Guide for Qualification of Measurement Methodsby a Laboratory Within the Nuclear Industry3C 1128 Guide for the Preparation of Working ReferenceMaterials for Use in the Analysis of Nuclear Fuel CycleMaterials3C 1133 Standard Test Met
10、hod for NDA of Special NuclearMaterial in Low Density Scrap and Waste by SegmentedPassive Gamma-Ray Scanning3C 1156 Guide for Establishing Calibration for a Measure-ment Method Used to Analyze Cycle Materials3C 1210 Guide for Establishing a Measurement SystemQuality Control Program for Analytical Ch
11、emistry Labo-ratories within the Nuclear Industry3C 1215 Guide for Preparing and Interpreting Precision andBias Statements in Test Method Standards Used in theNuclear Industry3C 1500 Test Method for Nondestructive Assay of Plutoniumby Passive Neutron Multiplicity Counting32.2 ANSI Standards:4ANSI 15
12、.20 Guide to Calibrating Nondestructive AssaySystemsANSI 15.35 Guide to Preparing Calibration Materials forNDA Systems that Count Passive Gamma-RaysANSI 15.36 Nondestructive Assay Measurement Controland Assurance1This practice is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and
13、is the direct responsibility of Subcommittee C26.10 on Nondestruc-tive Assay.Current edition approved Feb. 10, 2003. Published March 2003. Originallyapproved in 1991. Last previous edition approved in 1997 as C 120797.2The boldface numbers in parentheses refer to the list of references at the end of
14、this test method.3Annual Book of ASTM Standards, Vol 12.01.4Available from American National Standards Institute, 11 W. 42ndSt., 13thFloor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3. TerminologyThe followin
15、g definitions are needed in addition to thosepresented in ASTM C 859.3.1 Definitions:3.1.1 (a,n) reactionsoccur when energetic alpha particlescollide with low atomic number nuclei, such as O, F, or Mg,producing single neutrons.3.1.2 coincidence Gate Lengththe time interval followingthe detection of
16、a neutron during which additional neutrons areconsidered to be in coincidence with the original neutron.3.1.3 coincident neutronstwo or more neutrons emittedsimultaneously from a single event, such as from a nucleusduring fission.3.1.4 Dieaway timethe average life time of the neutronpopulation as me
17、asured from the time of emission to detection,escape, or absorption. The average life time is the time requiredfor the neutron population to decrease by a factor of 1/e. It isa function of several parameters including chamber design,detector design, assay item characteristics, and neutron energy.3.1
18、.5 iteman item refers to the entire scrap or wastecontainer being measured and its contents.3.1.6 matrixthe material which comprises the bulk of theitem, except for the special nuclear material and the container.This is the material in which the special nuclear material isembedded.3.1.6.1 benign mat
19、rixa matrix that has negligible effectson neutron transport. A benign matrix includes very littleneutron moderator.3.1.6.2 matrixspecific calibrationuses a calibration ma-trix similar to the matrix to be measured. No matrix correctionfactors are used. This calibration is generally not appropriatefor
20、 other matrices.3.1.7 neutron absorbersmaterials which have relativelylarge thermal-neutron absorption cross sections. Absorberswith the largest cross sections are commonly known as neutronpoisons. Some examples are lithium, boron, cadmium, andgadolinium.3.1.8 neutron moderatorsmaterials which slow
21、downneutrons. Materials containing large amounts of low atomicweight materials, e.g. hydrogen are highly moderating.3.1.9 passive neutron coincidence countinga techniqueused to measure the rate of coincident neutron emission in theassay item. The terminology used in this test method refersspecifical
22、ly to shift-register electronics (9, 10). Fig. 1 showsthe probability of detecting a neutron as a function of time andillustrates the time intervals discussed.3.1.9.1 Shift-register-based coincidence circuitan elec-tronic circuit for determining totals t, reals plus accidentals (r+ a), and accidenta
23、ls (a) in a selected count time t (9, 10). Shiftregister-based circuitry was developed to reduce dead times inthermal neutron coincidence counters. This technique permitsimproved measurement precision and operation at higher countrate ($ 100kHz).3.1.9.2 totals tthe total number of neutrons detectedd
24、uring the count time. This is a measured quantity.3.1.9.3 reals plus accidents, (r + a)the number of neu-trons detected in the (r+a) gate period (Fig. 1) following theinitial detection of each neutron. This is a measured quantityduring the count time (4, 9).3.1.9.4 accidentals, (a)the number of neut
25、rons detected inthe (a) gate period (Fig. 1) following the initial detection ofeach neutron during the selected count time t. This is ameasured quantity (4, 9).3.1.9.5 Reals, (r)This quantity is the difference betweenthe (r+a) and (a) quantities (4,9). It is proportional to thenumber of fissions in
26、the sample.3.1.10 Neutron multiplicationMultiplication takes placewhen a neutron interaction yields more than one neutron as aNOTE 1Curve (a) is a simplified probability distribution showing the approximately exponential decay, as a function of time, for detecting a secondneutron from a single fissi
27、on event. The probability for detecting a random neutron is constant with time. Typical coincidence timing parameters are shownin (b).FIG. 1 Probability of Detection as a Function of TimeC1207032product. Induced fission is the primary mechanism for neutronmultiplication, however (n,2n) interactions
28、are also multiplica-tion events.3.1.11 poisson assumptionFor passive neutron coinci-dence measurements, it is assumed that the net counts in a fixedperiod of time follow a Poisson distribution. This assumptioncan be verified by comparing the observed standard deviationof a series of measurements on
29、an item with the square root ofthe average number of counts. If the Poisson assumption iscorrect, these numbers should be equal within random error.3.1.12 PrecisionThe precision of a measurement is takento be the standard deviation or (percent) relative standarddeviation of a series of measurements
30、taken on the same itemunder essentially the same conditions.3.1.13 Pre-delaythe coincidence circuit has a pre-delayimmediately after a neutron has been detected to allow theamplifiers to recover and prepare to detect subsequent neu-trons. This principle is shown in Fig. 1.240Pu effective mass, meffi
31、s the mass of240Pu that wouldproduce the same coincident neutron response in the instru-ment as the assay item. It is correlated to the quantity of evenmass isotopes of plutonium in the assay item (11).3.1.15 transuranic waste (TRU waste)as defined in DOEOrder 5820.2 (12), transuranic waste is radio
32、active wastecontaining alpha-emitting isotopes with atomic number greaterthan 92 and half-life greater than 20 years, and with activityconcentrations greater than 100 nCi per gram of waste at thetime of the measurement.4. Summary of Test Method4.1 The even mass isotopes of plutonium fission spontane
33、-ously. On the average, two or more neutrons are emitted perfission event. The number of these coincident neutrons de-tected by the instrument is correlated to the quantity of evenmass isotopes of plutonium in the assay item, meff. The totalplutonium mass is determined from the known plutoniumisotop
34、ic ratios and the measured quantity of even massisotopes.4.2 The shift register technology is intended to correct forthe effects of accidental neutron coincidences.4.3 Other factors which may affect the assay are neutronmultiplication and matrix components with large (a, n) reac-tion rates, neutron
35、absorbers, or moderators. Corrections forthese effects are often not possible from the measurement dataalone, consequently assay items are sorted into material cat-egories or additional information is used to obtain the bestassay result.4.4 Corrections are typically made for electronic deadtimeand n
36、eutron background.4.5 Calibrations are based on measurements of well docu-mented and appropriate reference materials.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
37、 plutoniumcontent of scrap and waste in containers as large as 208-L(55-gal) drums. Total plutonium content ranges from 10 mg to6kg(1). The upper limit may be restricted to smaller massvalues depending on specific matrix, calibration material,criticality safety, or counting equipment considerations.
38、5.2 This test method is applicable for U.S. Department ofEnergy shipper/receiver confirmatory measurements (13),nuclear material diversion detection, and International AtomicEnergy Agency attributes measurements (14).5.3 This test method should be used in conjunction with ascrap and waste management
39、 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 plutonium isotopicratio, and hydrogen content. Packaging for each categoryshould be uniform with
40、respect to size, shape, and compositionof the container. Each material category will require calibrationstandards and may have different plutonium mass limits.5.4 Bias in passive neutron coincidence measurements isrelated to item size and density, the homogeneity and compo-sition of the matrix, and
41、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.5.4.1 For both benign matrix and matrix specific measure-ments, the method assumes the calibrati
42、on 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 theextent they affect the measurement.5.4.2 Measurements of smaller containers containing scrapand
43、waste are generally more accurate than measurements of208-L (55-gal) drums.5.4.3 It is recommended that measurements be made onitems with homogeneous contents. Heterogeneity in the distri-bution of nuclear material, neutron moderators, and neutronabsorbers have the potential to cause biased results.
44、5.5 The coincident neutron production rates measured bythis test method are proportional to the mass of the evennumber isotopes of plutonium. If the relative abundances ofthese isotopes are not accurately known, biases in the totalplutonium assay value will result.5.6 A typical count time is 1000 se
45、conds.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. Training guidance is available from ANSI15.20, ASTM C 1009, ASTM C 986, and ASTM C 1068.6. Interferences6.
46、1 Conditions affecting measurement uncertainty includeneutron background, moderators, multiplication, large (a,n)rates, absorbers, matrix and nuclear material heterogeneity, andother sources of coincident neutrons. It is usually not possibleto detect these problems or to calculate corrections for th
47、eseeffects 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 as low and as constant as practical. Corrections can beC1207033made for the effects of high-
48、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 willalso increase multiplication effects. Consequently, the mea-sured neutron rates
49、may be either smaller or larger than thosefor a nonmoderating matrix. Hydrogenous matrices contributethe most to this effect (15).6.4 Both spontaneous and induced fissions produce coinci-dent neutrons. The instrument, however, cannot distinguishbetween them. Three factors that strongly affect the degree ofmultiplication are the mass of fissile material, its density, andits geometry. Increases in mass that are not accompanied bychanges in either density or geometry will result in predictablemultiplication increases that can be incorporated into thecalibration fun
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