1、Designation: C1807 15Standard Guide forNondestructive Assay of Special Nuclear Material (SNM)Holdup Using Passive Neutron Measurement Methods1This standard is issued under the fixed designation C1807; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case 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 guide describes passive neutron measurementmethods used to nondestructively estimat
3、e the amount ofneutron-emitting special nuclear material compounds remain-ing as holdup in nuclear facilities. Holdup occurs in allfacilities in which nuclear material is processed. Material mayexist, for example, in process equipment, in exhaust ventilationsystems, and in building walls and floors.
4、1.1.1 The most frequent uses of passive neutron holduptechniques are for the measurement of uranium or plutoniumdeposits in processing facilities.1.2 This guide includes information useful for management,planning, selection of equipment, consideration ofinterferences, measurement program definition,
5、 and the utili-zation of resources.1.3 Counting modes include both singles (totals) or grosscounting and neutron coincidence techniques.1.3.1 Neutron holdup measurements of uranium are typi-cally performed on neutrons emitted during (, n) reactions andspontaneous fission using singles (totals) or gr
6、oss counting.While the method does not preclude measurement usingcoincidence or multiplicity counting for uranium, measurementefficiency is generally not sufficient to permit assays inreasonable counting times.1.3.2 For measurement of plutonium in gloveboxes, in-stalled measurement equipment may pro
7、vide sufficient effi-ciency for performing counting using neutron coincidencetechniques in reasonable counting times.1.4 The measurement of nuclear material holdup in processequipment requires a scientific knowledge of radiation sourcesand detectors, radiation transport, modeling methods,calibration
8、, facility operations, and uncertainty analysis. It issubject to the constraints of the facility, management, budget,and schedule, plus health and safety requirements, as well asthe laws of physics. This guide does not purport to instruct theNDA practitioner on these principles.1.5 The measurement p
9、rocess includes defining measure-ment uncertainties and is sensitive to the chemicalcomposition, isotopic composition, distribution of the material,various backgrounds, and interferences. The work includesinvestigation of material distributions within a facility, whichcould include potentially large
10、 holdup surface areas. Nuclearmaterial held up in pipes, ductwork, gloveboxes, and heavyequipment is usually distributed in a diffuse and irregularmanner. It is difficult to define the measurement geometry,identify the form of the material, and measure it.1.6 UnitsThe values stated in SI units are t
11、o be regardedas the standard. No other units of measurement are included inthis standard.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 practice
12、s and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C1009 Guide for Establishing and Maintaining a QualityAssurance Program forAnalytical Laboratories Within theNuclear IndustryC1455 Test Method for Nondestructive Assay of SpecialNucle
13、ar Material Holdup Using Gamma-Ray Spectro-scopic MethodsC1490 Guide for the Selection, Training and Qualification ofNondestructive Assay (NDA) PersonnelC1592/C1592M Guide for Making Quality NondestructiveAssay MeasurementsC1673 Terminology of C26.10 Nondestructive Assay Meth-ods2.2 NRC Standard:NRC
14、 Regulatory Guide 5.23 In-Situ Assay of PlutoniumResidual Holdup31This guide is under the jurisdiction of ASTM Committee C26 on Nuclear FuelCycle and is the direct responsibility of Subcommittee C26.10 on Non DestructiveAssay.Current edition approved Jan. 1, 2015. Published January 2015. DOI: 10.152
15、0/C1807-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from U. S. Nuclear Regulatory Commissio
16、n (NRC), One White FlintNorth, 11555 Rockville Pk., Rockville, MD 20852-2738, http:/www.nrc.gov.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12.3 ANSI Standard:ANSI N15.20 Guide to Calibrating Nondestructive AssaySystems43. Terminol
17、ogy3.1 DefinitionsRefer to Terminology C1673 for defini-tions used in this guide.4. Summary of Guide4.1 IntroductionHoldup measurements using neutronmethods typically measure the (, n) or spontaneous fissionproduction of neutrons, or both. Neutrons generated in itemsthat do not include significant m
18、asses of neutron moderators,such as hydrogenous materials, typically have an escapefraction of nearly one. The isotopic distribution and, for (,n)production, the chemical composition of the measured materialaffect assay results and shall be determined by process knowl-edge or an alternative measurem
19、ent technique. Ref (1)5pro-vides an example of a holdup campaign using neutron mea-surements.4.2 Choice of Measurement MethodPassive neutron mea-surement methods are typically used for holdup when othermethods of measurement (for example, gamma-ray assay) arenot practical or would produce large bias
20、es. In some cases,neutron measurements are performed in conjunction withgamma-ray measurements for defense in depth or to obtainisotopic information, or both. Neutron measurement instru-mentation is typically heavier, more difficult to shield, and hasmore difficult data interpretation than other NDA
21、 measurementmethods. Neutrons, though, are very penetrating and lessinfluenced by lumps than gamma rays, and the instrumentationhas a very stable response. Examples of when neutron mea-surements are preferred include containers that severely attenu-ate gamma rays of interest for the nuclides measure
22、d or whensufficient nuclear material is present that self-attenuation ofgamma rays of interest is severe (see Test Method C1455 andGuide C1592/C1592M).4.3 Specific Neutron YieldThe number of neutrons gener-ated per unit time per unit mass of the nuclide(s) of interest isan important parameter that i
23、s affected by conditions (forexample, chemical composition and isotopic distribution) notdetectable by passive neutron holdup measurement methods.Information used to estimate specific neutron yield shall bedetermined using process knowledge or alternate analysismethods (for example, sampling and X-r
24、ay fluorescence todetermine chemical composition and high-resolution gamma-ray spectroscopy to determine isotopic composition). Both thechemical and isotopic distribution have significant effects onspecific neutron yield.4.4 Definition of RequirementsDefinition of the holdupmeasurement requirements
25、should include, as a minimum, themeasurement objectives (that is, nuclear criticality safety,special nuclear material (SNM) accountability, radiologicalsafety, or combinations thereof); time and resource constraints;the desired measurement sensitivity, accuracy, and uncertainty;and available resourc
26、es (schedule, funds, and subject matterexperts). Specific data quality objectives should be providedwhen available.4.5 Information Gathering and Initial EvaluationInformation shall be gathered concerning the item or items tobe assayed, and an initial evaluation should be made of themeasurement techn
27、iques and level of effort needed to meet theholdup measurement requirements. Preliminary radiation mea-surements may be needed to define the location and extent ofthe holdup. Additional information should be collected prior tocommencement of measurements. This information includes,but is not limited
28、 to, the geometric configuration of the item orprocess equipment to be assayed, location of the equipment inthe facility, the presence of neutron moderators and absorbers,neutron leakage multiplication, factors affecting specific neu-tron yield, sources of background or interferences, facilityproces
29、sing status, radiological and industrial safetyconsiderations, plus the personnel and equipment needed tocomplete the assay. Sources of information may include avisual survey, engineering drawings, process knowledge, pro-cess operators, results of sampling and wet chemical analysis,and prior assay d
30、ocumentation.4.6 Measurement PlanA measurement plan shall be de-veloped. The initial evaluation provides a basis for choosingthe quantitative method and assay model and, subsequently,leads to the determination of the detection system and calibra-tion method to be used. Appropriate reference material
31、s andsupport equipment are developed or assembled for the specificmeasurement technique. The plan will include measurementlocations and geometries or guidance for their selection. In theplan, required documentation; operating procedures; back-ground measurement methods and frequencies; plus training
32、,quality, and measurement control requirements (Guide C1009)are typically outlined. Necessary procedures, including thosefor measurement control, shall be developed, documented, andapproved.4.7 CalibrationCalibration and initialization of measure-ment control is completed before measurements of unkn
33、owns.Calibration requires reference materials traceable to a NationalMeasurement Institute to establish detection efficiency andmodeling detector response to neutron sources. If modeling isused for calibration (for example, Monte Carlo n-Partical(MCNP) modeling), detailed specifications for the dete
34、ctorpackage will be required. If modeling is used, validation of thecalibration shall include validation of each model developed.Familiarity with the facility on which assays will be performedis required to ensure that calibration is sufficiently robust toencompass all reasonable measurement situati
35、ons.4.7.1 Calibration Using252Cf252Cf is commonly used forcalibrating neutron detectors.252Cf is convenient in that itprovides a point source of neutron emissions with a strongsignal so that calibrations can be completed using relativelyshort measurement times. Corrections for the difference indetec
36、tion efficiency between neutrons from252Cf and neutronsfrom assayed items may be significant because of the differ-ence in average energy from the two sources. For example, the4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.o
37、rg.5The boldface numbers in parentheses refer to a list of references at the end ofthis standard.C1807 152average energy of neutrons from252Cf is 2.14 MeV and theaverage energy of neutrons from holdup is 1.2 MeV for (,n)with Fluorine as a target and an alpha energy of 5.2 MeV (2).An additional issue
38、 is that252Cf standards are typicallycertified for total neutron activity, and isotopes present in thestandards produce an increasing number of neutrons as themass of252Cf decreases relative to the mass of longer-livedisotopes as time passes. As the time since separation of the252Cf increases, this
39、may become a significant source of biasunless appropriate corrections are made.4.7.2 Calibration Using Surrogate MaterialsSurrogatematerials, typically created using the same materials that willbe subsequently measured, may also be used for calibration,provided sufficient characterization is perform
40、ed to establishtraceability. These sources typically produce fewer neutronsper unit time than252Cf and require longer measurement timesfor equivalent calibration uncertainty. In addition, surrogatematerials are typically significantly larger than point sources,which may complicate the process of eva
41、luating calibrationdata. Calibration using surrogate materials reduces the numberof corrections (for example, for energy difference betweenneutrons produced by the calibration source and measuredmaterials) and may result in a lower total measurementuncertainty.4.7.3 Calibration ConfirmationA calibra
42、tion confirmationis needed to produce objective evidence demonstrating theapplicability and correctness of the calibration relative to theitems in which holdup is to be measured. The recommendedmethod is to assemble test item(s) consisting of source/matrixand radioactive material configuration(s) no
43、minally represen-tative of the items to be characterized. The test item(s) shouldcontain known and, preferably, traceable quantity of radioac-tive material in a known and representative configuration. Ifpractical, the range of expected materials should be spanned.Acceptance criteria for the calibrat
44、ion confirmation measure-ments should be established in the measurement plan.4.8 MeasurementsPerform measurements and measure-ment control as detailed in the measurement plan or procedure.4.9 Evaluation of Measurement DataAs appropriate, cor-rections are estimated and made for factors that may bias
45、themeasurement. Examples include neutron scattering; cosmic rayinduced spallation; leakage multiplication; neutron moderators,absorbers, and poisons; and the presence of targets that produce(, n) neutrons. These corrections are applied in the calculationof the assay value. Measurement uncertainties
46、are establishedbased on factors affecting the assay.4.9.1 Converting measurement data to estimates of thequantity of nuclear material holdup requires careful evaluationof the measurement parameters against calibration and model-ing assumptions. Depending on the calibration, models, andmeasurement me
47、thods used, corrections may be necessary forgeometric effects (differences between holdup measurementand calibration geometries); neutron moderators, absorbers, orpoisons; scattering from nearby process equipment; the influ-ence (scattering and shielding) of and holdup in nearby processequipment tha
48、t is in the detector field of view; background; andinterferences. Measurement uncertainties (random and item-specific bias) are estimated based on uncertainties in assayparameters. A comprehensive total measurement uncertaintyanalysis must accompany every measurement result.4.9.2 Results should be e
49、valuated against previous results orclean-out data, if either are available. This evaluation providesa cross-check between measurement techniques. The results ofthis evaluation can be used to provide feedback to measure-ment personnel, to refine the measurement and analysistechniques, and to evaluate the measurement uncertaintyagainst estimates. If a discrepancy is evident, an evaluationshould be made. Modeling errors or other sources of bias canbe identified using this technique. Additional measurementswith subsequent evaluation may be required. This can be useda
