1、Designation: C 1493 01Standard Test Method forNon-Destructive Assay of Nuclear Material in Waste byPassive and Active Neutron Counting Using a DifferentialDie-Away System1This standard is issued under the fixed designation C 1493; the number immediately following the designation indicates the year o
2、foriginal 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 a system that performs nonde-stru
3、ctive assay (NDA) of uranium or plutonium, or both, usingthe active, differential die-away technique (DDT), and passiveneutron coincidence counting. Results from the active andpassive measurements are combined to determine the totalamount of fissile and spontaneously-fissioning material indrums of s
4、crap or waste as large as 208 L. Corrections aremade to the measurements for the effects of neutron modera-tion and absorption, assuming that the effects are averaged overthe volume of the drum and that no significant lumps of nuclearmaterial are present. These systems are most widely used toassay l
5、ow-level and transuranic waste, but may also be used forthe measurement of scrap materials. While this test method isspecific to the second-generation Los Alamos National Labo-ratory (LANL) passive-active neutron assay system, the prin-ciple applies to other DDT systems.1.1.1 In the active mode, the
6、 system measures fissile iso-topes such as235U and239Pu. The neutrons from a pulsed,14-MeV neutron generator are thermalized to induce fission inthe assay item. Between generator pulses, the system detectsprompt-fission neutrons emitted from the fissile material. Thenumber of detected neutrons betwe
7、en pulses is proportional tothe mass of fissile material. This method is called the differ-ential die-away technique.1.1.2 In the passive mode, the system detects time-coincident neutrons emitted from spontaneously fissioningisotopes. The primary isotopes measured are238Pu,240Pu,and242Pu; however, t
8、he system may be adapted for use onother spontaneously-fissioning isotopes as well. The number ofcoincident neutrons detected is proportional to the mass ofspontaneously-fissioning material.1.2 The active mode is used to assay fissile material in thefollowing ranges.1.2.1 For uranium-bearing items,
9、the DDT can measurethe235U content in the range from 0.02 to over 100 g.Normally, the assay of items bearing only uranium is per-formed using matrix-specific calibrations to account for theeffect of the matrix on the active signal.1.2.2 For plutonium-bearing items, the DDT method mea-sures the239Pu
10、content in the range between 0.01 and 20 g.1.3 The passive mode is capable of assaying spontaneously-fissioning nuclei, over a nominal range from 0.05 to 15 gof240Pu, or equivalent. The passive mode can also be used tomeasure large (for example, kg) quantities of238U.1.4 This test method requires kn
11、owledge of the relativeabundances of the plutonium or uranium isotopes to determinethe total plutonium or uranium mass.1.5 This test method will give biased results when the wasteform does not meet the calibration specifications and themeasurement assumptions presented in this test method regard-ing
12、 the requirements for a homogeneous matrix, uniformsource distribution, and the absence of nuclear material lumps,to the extent that they effect the measurement.1.6 The complete active and passive assay of a 208 L drumis nominally 10 min or less.1.7 Improvements to this test method have been reporte
13、d (1,2, 3, 4).2Discussions of these improvements are not includedin this test method.1.8 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 use
14、r of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.Specific precautionary statements are given in Section 8.2. Referenced Documents2.1 ASTM Standards:C 859 Terminology Relating to Nuclear Materials3C 986 Guid
15、e 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 of Plutonium Isoto-pic Composition by Gamma-Ray Spectrometry31This test method
16、is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on Non-Destructive Assay.Current edition approved Feb. 10, 2001. Published May 2001.2The boldface numbers given in parentheses refer to a list of references at theend of the t
17、ext.3Annual Book of ASTM Standards, Vol 12.01.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.C 1068 Guide for Qualification of Measurement Methodsby a Laboratory within the Nuclear Industry3C 1128 Guide for the Preparation of Working ReferenceMaterials for Us
18、e in the Analysis of Nuclear Fuel CycleMaterials3C 1156 Guide for Establishing Calibration for a Measure-ment Method used to Analyze Nuclear fuel Cycle Materi-als3C 1207 Test Method for Nondestructive Assay of Plutoniumin Scrap and Waste by Passive Neutron CoincidenceCounting3C 1210 Guide for Establ
19、ishing a Measurement SystemQuality Control Program for Analytical Chemistry Labo-ratories within the Nuclear Industry3C 1215 Guide for Preparing and Interpreting Precision andBias Statements in Test Method Standards used in theNuclear Industry32.2 ANSI Standard:ANSI N15.20 Guide to Calibrating Nonde
20、structive AssaySystems42.3 U.S. Government Documents:DOE Order 435.1 (supercedes DOE Order 5820.2A Radio-active Waste ManagementDOE Order 474.1 (supercedes DOE Order 5633.3B) Con-trol and Accountability of Nuclear MaterialsDOE Order 5630.2 Control and Accountability of NuclearMaterials, Basic Princi
21、plesDOE /WIPP-069 Waste Acceptance Criteria for the WasteIsolation Pilot Plant10CFR71 Packaging and Transport of Radioactive Materi-als40CFR191 Environmental Radiation Protection Standardsfor Management and Disposal of Spent Nuclear Fuel,High-Level, and Transuranic Radioactive WasteUSNRC Regulatory
22、Guide 5.11 Nondestructive Assay ofSpecial Nuclear Materials Contained in Scrap and WasteUSNRC Regulatory Guide 5.53 Qualification, Calibration,and Error Estimation Methods for Nondestructive Assay3. Terminology3.1 DefinitionsThe following definitions are needed inaddition to those presented in Termi
23、nology C 859.3.1.1 active mode, ndetermines total fissile mass of theassayed item through thermal neutron interrogation and sub-sequent detection of prompt-fission neutrons released frominduced fission. A 14-MeV neutron generator is pulsed at anominal rate of 50 Hz. The pulsed neutrons rapidly therm
24、alizein the chamber and in the assay item. Thermal neutrons arecaptured by fissile material which then fissions and immedi-ately releases more neutrons which are detected prior to theinitiation of the next pulse. The prompt-neutron count rate isproportional to the mass of fissile material. This mode
25、 is calledthe differential die-away technique (DDT). Refer to Fig. 1.3.1.2 (alpha, n) reactions, noccur when energetic alphaparticles collide with low atomic number nuclei such as18O, F,or Mg producing single neutrons. Neutrons produced in thismanner are not correlated in time and are a source ofacc
26、identals in passive mode and background in active mode.3.1.3 coincidence gate length, nthe time interval follow-ing the detection of a neutron during which additional neutroncounts are considered to be in coincidence with the originalneutron. Coincidence gate lengths are generally determined bythe d
27、ie-away time of the detector package. The gate length fora shielded detector package is nominally between 35 and 70 s.The gate length for a bare detector package is nominally 250s.3.1.4 coincident neutrons, ntwo or more neutrons emittedsimultaneously from a single event, such as from a nucleusduring
28、 fission.3.1.5 combined passive and active, na method which usespassive and active modes to determine the spontaneously-fissioning and fissile mass components of the waste form,respectively.3.1.6 depleted uranium, nuranium containing less thanthe naturally occurring fraction of235U isotopes ( 0.7 we
29、ightpercent).3.1.7 die-away time, nthe average lifetime of the neutronpopulation in an NDA assay system as measured from the timeof emission to detection, escape, or absorption. The averagelifetime is the time required for the neutron population todecrease by a factor of 1/e. It is a function of sev
30、eralparameters including chamber design, detector design, assayitem characteristics, and neutron energy.3.1.8 early gate, nthe time interval during which thethermal-neutron induced prompt-fission neutrons are mea-sured. Typically, this time interval begins 0.4 to 0.9 ms after theinitiating neutron g
31、enerator pulse and is 2 to 4 ms in duration.This gate is used only during the active mode. Fig. 1 indicatesthe approximate delay and length of the early gate in referenceto a generator pulse.3.1.9 fissile isotopes, nisotopes that can be induced tofission by neutrons with thermal kinetic energy, abou
32、t 0.025electron volts.233U,235U,239Pu, and241Pu are the mostcommon fissile isotopes.3.1.10 flux monitors, ndetectors in the measurementchamber. There are two types of flux monitors:3.1.10.1 cavity flux monitor, nbare neutron detectors usedto monitor the intensity of the interrogating thermal neutron
33、flux in the chamber.3.1.10.2 drum flux monitors, nbare neutron detectorsplaced close to the drum and collimated with cadmium tomeasure the thermal neutron flux emitted from the drum.3.1.11 late gate, nthe time interval during which theactive neutron background is measured. Typically, this timeinterv
34、al begins 8 to 18 ms after the initiating neutron generatorpulse. Refer to Fig. 1.3.1.12 lump, nthat contiguous mass of nuclear materialthat is sufficiently large to affect the measured signal. In theactive mode, self-shielding of the thermal neutron interrogatingflux results in an underestimation o
35、f the fissile mass. In thepassive mode, self-multiplication leads to an overestimation ofthe spontaneous-fissioning mass.3.1.13 matrix, nthe material which comprises the bulk of4Available from American National Standards Institute, 11 W. 42nd St., 13thFloor, New York, NY 10036.C 14932the item, excep
36、t for the assay isotopes and the container.3.1.14 matrix-specific calibration, nuses a calibration ma-trix for both passive and active assays similar to the matrix tobe measured. No matrix correction factors are used. Thiscalibration is generally not appropriate for other matrices.3.1.15 neutron abs
37、orbers, nmaterials which have rela-tively large thermal-neutron capture cross-sections. Absorberswith the largest capture cross-sections are commonly known asneutron poisons. Some examples are boron, cadmium, gado-linium and lithium.3.1.16 neutron detector package, na bundle of two orthree, 2- or 3-
38、ft long neutron proportional detectors (forexample,3He tubes) surrounded by polyethylene. The output ofthe detectors from one package is combined into one signal andprocessed by a single preamplifier/amplifier/ discriminator.Neutron detector packages are of two types:3.1.16.1 bare detector package,
39、nneutron detectors sur-rounded by polyethylene, but not shielded with cadmium.These packages provide a better efficiency for thermal neu-trons, thus providing a better passive sensitivity when a smallamount of nuclear material is present.3.1.16.2 shielded detector package, nneutron detectorssurround
40、ed by polyethylene and shielded by a thin wrapping ofcadmium. These packages measure the neutrons produced bynuclear interactions and are relatively insensitive to thermal-ized neutrons.3.1.17 neutron moderators, nmaterials which slow downneutrons through elastic scattering interactions. Materials c
41、on-taining large amounts of low atomic weight materials, forexample, hydrogen, are highly moderating.3.1.18 passive mode, na technique used to determine thespontaneously-fissioning mass in the measured item throughthe detection of coincident neutrons. The coincident neutronsare prompt neutrons.3.1.1
42、9240Pu-effective mass, meff, nthe mass of240Pu thatwould produce the same coincident neutron response in theinstrument as the assay item. It is a function of the quantity ofeven mass isotopes of plutonium in the assay item andfundamental nuclear constants.3.1.20 prompt neutrons, nneutrons released w
43、ithin ap-proximately 10-14s of the fissioning event. For example, onaverage,235U and239Pu emit 2.41 and 2.88, respectively,prompt neutrons per neutron-induced fission event.240Pu emitson an average of 2.16 neutrons per spontaneous fission event.3.1.21 pulsed neutron generator, na device which cansup
44、ply a pulsed flux of neutrons. A widely used generator is thezetatron which produces 14-MeV neutrons via the deuterium-tritium interaction. Zetatrons generate a 10 to 20 s pulse at afrequency of 50 Hz.3.1.22 spontaneously-fissioning nuclei, nthose nucleiwhich do not require an external neutron sourc
45、e to undergoFIG. 1 Time History of an Active Assay of Plutonium Using the Differential Die-Away TechniqueC 14933fission. The most common isotopes are238Pu,240Pu,242Pu,244Cm and252Cf.3.1.23 totals, ntotal number of individual neutrons de-tected during the count time, t.3.1.23.1 bare totals, nis the s
46、um of neutrons detectedfrom all bare detector packages.3.1.23.2 shielded totals, nis the sum of neutrons detectedfrom all shielded detector packages.3.1.23.3 system totals, nis the sum of neutrons detected inboth the bare and shielded detector packages.3.1.24 transuranic waste, TRU waste, nas define
47、d byDOE Order 435.1 (5), transuranic waste is radioactive wastecontaining alpha-emitting isotopes with atomic number greaterthan 92, half-life greater than 20 years, and with activityconcentration greater than 100 nCi per gram of waste at thetime of the assay.3.1.25 volume weighted average response,
48、 nan estimateof the count rate that would be obtained from a drumcontaining a uniform distribution of special nuclear material. Itis a weighted average calculated from a series of measurementsas follows: the drum is divided into typically 10 to 15 volumeelements, a point source is centered in one of
49、 the volumeelements and measured, the point source is moved to the nextvolume element and measured, and each response is weightedby the size of the corresponding element. See Appendix X1 fora more detailed explanation.3.1.26 wide-range calibration, na calibration techniquefor both passive and active assays that uses calibration sourcesin a variety of homogeneous mock matrices whose moderationand absorption properties span the range expected to beencountered in the waste drums for which the calibration is tobe used. Relationships between the measured qua
