1、Designation: C1455 141Standard Test Method forNondestructive Assay of Special Nuclear Material HoldupUsing Gamma-Ray Spectroscopic Methods1This standard is issued under the fixed designation C1455; 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 () indicates an editorial change since the last revision or reapproval.1NOTE10.4.1.1 editorially corrected in July 2015.1. Scope1.1 This test method describes gamma-ray metho
3、ds used tonondestructively measure the quantity of235Uor239Pu presentas holdup in nuclear facilities. Holdup may occur in anyfacility where nuclear material is processed, in processequipment, in exhaust ventilation systems and in building wallsand floors.1.2 This test method includes information use
4、ful formanagement, planning, selection of equipment, considerationof interferences, measurement program definition, and theutilization of resources (1, 2, 3, 4).21.3 The measurement of nuclear material hold up in processequipment requires a scientific knowledge of radiation sourcesand detectors, tra
5、nsmission of radiation, calibration, facilityoperations and uncertainty analysis. It is subject to the con-straints of the facility, management, budget, and schedule; plushealth and safety requirements. The measurement processincludes defining measurement uncertainties and is sensitive tothe form an
6、d distribution of the material, various backgrounds,and interferences. The work includes investigation of materialdistributions within a facility, which could include potentiallylarge holdup surface areas. Nuclear material held up in pipes,ductwork, gloveboxes, and heavy equipment, is usually dis-tr
7、ibuted in a diffuse and irregular manner. It is difficult to definethe measurement geometry, to identify the form of the material,and to measure it without interference from adjacent sources ofradiation.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with
8、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 Documents2.1 ASTM Standards:3C1490 Guide for the Selection, Training and Qualification ofNondestru
9、ctive Assay (NDA) PersonnelC1592 Guide for Nondestructive Assay MeasurementsC1673 Terminology of C26.10 Nondestructive Assay Meth-ods2.2 ANSI Standards:4ANSI N15.36 Measurement Control ProgramNondestructive Assay Measurement Control and Assur-ance SystemsANSI N15.56 Nondestructive Assay Measurements
10、 ofNuclear Material Holdup: General Provisions2.3 U.S. Nuclear Regulatory Commission RegulatoryGuides:5Regulatory Guide 5.23, In Situ Assay of Plutonium ResidualHoldup3. Terminology3.1 Refer to Terminology C1673 for definitions used in thistest method.4. Summary of Test Method4.1 IntroductionHoldup
11、measurements range from thesolitary assay of a single item or routine measurement of apiece of equipment, to an extensive campaign of determiningthe total SNM in-process inventory for a processing plant.Holdup measurements differ from other nondestructive mea-surement methods in that the assays are
12、performed in situ onequipment or items instead of on multiple items with similarcharacteristics measured in a specialized, isolated room. Oftenthe chemical form and geometric distribution of the SNM are1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the
13、direct responsibility of Subcommittee C26.10 on NonDestructive Assay.Current edition approved Jan. 1, 2014. Published March 2014. Originallyapproved in 2000. Last previous edition approved in 2007 as C1455 07. DOI:10.1520/C1455-14E01.2The boldface numbers in parentheses refer to the list of referenc
14、es at the end ofthis standard.3For 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.4Available from American Nation
15、al Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.5Available from the U.S. Nuclear Regulatory Commission, Washington, DC,20555.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1not well know
16、n. These challenges require unique preparationfor every measurement to obtain a quality result. Unknownmeasurement parameters can lead to large measurement uncer-tainties.4.2 Definition of RequirementsDefinition of the holdupmeasurement requirements should include, as a minimum, themeasurement objec
17、tives (that is, criticality control, SNMaccountability, safety, or combinations thereof); the desiredmeasurement sensitivity, measurement uncertainty, and avail-able resources (schedule, funds, and subject matter experts).The customer, the measurement organization, and appropriateregulatory authorit
18、ies should agree on the holdup measurementrequirements before holdup measurements commence.4.3 Information Gathering and Initial EvaluationInformation must be gathered concerning the item or items tobe assayed and an initial evaluation should be made of the levelof effort needed to meet the holdup m
19、easurement requirements.Preliminary measurements may be needed to assess theproblem, to define the location and extent of the holdup, todetermine the SNM isotopic composition or enrichment, and toidentify potential interfering radionuclides. Factors to be con-sidered include the geometric configurat
20、ion of the item orprocess equipment to be assayed, location of the equipment inthe facility, attenuating materials, sources of background orinterferences, facility processing status, radiological and indus-trial safety considerations, plus the personnel and equipmentneeded to complete the assay. Sou
21、rces of information mayinclude a visual survey, engineering drawings, processknowledge, process operators, and prior assay documentation.4.3.1 Subsequent measurement campaigns may well pro-ceed more rapidly when the objective is to quantify changesfrom the previous measurement campaigns and no chang
22、eshave been made to the process.4.3.2 Shutdown facilities are frequently measured once-through carefully and completely. Any subsequent measure-ment campaigns may only verify a subset of the data set.4.4 Task Design and PreparationThe initial evaluationprovides a basis for choosing the quantitative
23、method, assaymodel, and subsequently leads to determination of the detec-tion system and calibration method to be used. Appropriatestandards and support equipment are developed or assembledfor the specific measurement technique. A measurement planshould be developed. The plan will include measuremen
24、tlocations and geometries or guidance for their selection. Themeasurement plan will reference overall measurement programdocuments governing required documentation, operatingprocedures, background measurement methods andfrequencies, plus training, quality and measurement controlrequirements. Any nee
25、ded additional procedures should bedeveloped, documented, and approved.4.5 CalibrationCalibration and initialization of measure-ment control should be completed before measurements ofunknowns. Calibration requires traceable standards.4.6 MeasurementsPerform measurements and measure-ment control as d
26、etailed in the measurement plan or procedure.4.7 Evaluation of Measurement DataAs appropriate, cor-rections to measured count rates are made for Comptonbackground, gamma-ray attenuation effects by equipmentwalls, and measured area background. As appropriate, correc-tions are made for finite geometry
27、 effects in the assay modeland for self-attenuation. These corrections are applied in thecalculation of the assay value. Measurement uncertainties areestablished based on factors affecting the assay.4.7.1 Converting measurement data to estimates of thequantity of nuclear material holdup requires car
28、eful evaluationof the measurement parameters against calibration assump-tions. Depending on the calibration and measurement methodsused, corrections may be necessary for geometric effects(differences between holdup measurement and calibrationgeometries), gamma-ray attenuation effects, background, an
29、dinterferences. Measurement uncertainties (random and system-atic) are estimated based on uncertainties in assay parameters,for example, holdup distribution, attenuation effects, measuredcount rates and finite source corrections.4.7.2 Results should be evaluated against previous results, ifavailable
30、. If a discrepancy is evident, an evaluation should bemade. Additional measurements with subsequent evaluationmay be required.4.8 DocumentationMeasurement documentation shouldinclude the plans and procedures, a description of measurementparameters considered important to the calibration and mea-sure
31、ment location, the measurement techniques used, the rawdata, the assumptions and correction factors used in theanalysis, the results with estimated uncertainty, and compari-son to other measurement techniques (when available).5. Significance and Use5.1 Measurement results from this test method assis
32、ts indemonstrating regulatory compliance in such areas as safe-guards SNM inventory control, criticality control, wastedisposal, and decontamination and decommissioning (D properindustrial safety practices for working with cryogenic liquidsmust be followed.8.2 Technical Hazards:8.2.1 High gamma-ray
33、flux generally will cause pulsepileup, which affects the observed energy and resolution of thepeaks, as well as, the total counts observed in the peaks due tosumming effects. Extremely high activity holdup may saturatethe electronics of certain types of preamplifiers resulting in nocounts being regi
34、stered by the equipment. Dead timeindication from the measurement electronics will often identifythis problem. Preliminary scan measurements (5.2) may alsoidentify this problem.8.2.2 Electronic instability can significantly alter assay re-sults. For example, electrical noise or microphonics candegra
35、de the energy resolution of the spectra.8.2.3 Secular Equilibrium (Terminology C1673)If thegamma ray from a daughter radionuclide is used to quantifyholdup, such as with238U and234mPa, secular equilibriumwithin the holdup should be verified. Process knowledge andhistory may provide the necessary inf
36、ormation to determine ifsecular equilibrium has been established. If secular equilibriumis assumed but not established measurement results could bebiased.8.2.4 Infinitely Thick (Terminology C1673) SNMHoldupIf the holdup deposit is infinitely thick to the mea-surement of gamma rays, transmission corr
37、ections are notsimple to perform and the measurement results will likely bebiased low.8.2.4.1 Reference (3) provides a detailed discussion on thecorrections for thick deposits and the limitations of suchcorrections. The discussion in reference (3) applies directly tothe GGH method although the princ
38、iples discussed are appli-cable to all measurements.8.2.5 BackgroundA lack of understanding of backgroundeffects on the measurement or incorrect background measure-ments may impact the results significantly. Neither measure-ment items nor items affecting background should be movedduring measurements
39、.8.2.5.1 Care must be taken to position the detector toproperly account for background.8.2.6 Temperature changes at the measurement locationmay result in a detector gain drift. Stabilization methods maybe necessary to mitigate this effect.8.2.7 Unexpected presence of bremsstrahlung in the spectramay
40、 cause a bias in low resolution measurements. Forexample, bremsstrahlung caused by99Tc or the238U daughter,234mPa.9. Procedure9.1 A Holdup Measurement Campaign Procedure generallyincludes the following:9.1.1 Development (or Review) of Measurement Strategyand Development (or Review) of Detailed Measu
41、rement Plan,9.1.2 Preparation for Measurements,9.1.3 Calibration or Model Development,9.1.4 Performance of Measurements,9.1.5 Calculations (often in parallel while the data isacquired),9.1.6 Estimation of Measurement Uncertainty (typicallyPrecision and Bias), and,9.1.7 Recording of data and results
42、(3, 4, 9, 10, 11) NRCRegulatory Guide 5.23).9.2 ProcedureMeasurement Strategy/Plan Development:9.2.1 Measurement Program RequirementsPrior to theevaluation of a holdup measurement or campaign, specificinformation must be gathered regarding what is expected of themeasurement or measurement program. T
43、he informationshould provide the boundaries for the task or project. Thisinformation typically includes the following:9.2.1.1 Identification of item(s) or piece(s) of equipment tobe measured.9.2.1.2 Radionuclide or radionuclides of interest.9.2.1.3 Acceptable level of measurement uncertainty.9.2.1.4
44、 Acceptable lower detection limit for the assay.9.2.1.5 Intended applications for results, for example, criti-cality risk assessment, SNM accountability, health physics, ordecontamination and demolition.9.2.1.6 Administrative requirements, for example, qualityassurance requirements, documentation an
45、d reporting require-ments.9.2.2 Resource Constraints:9.2.2.1 The time available to perform the measurement(s),analyze the data and report the results.C1455 14149.2.2.2 Resources available to perform the individual mea-surement or the measurement program.9.2.3 Personnel and ProceduresThere are typica
46、lly twolevels of procedures: (1) generic or all-encompassing such asthe measurement strategy or selection of models, and (2) thedetailed work instructions for each data acquisition:9.2.3.1 Formal procedures may be developed for the itemmeasurements. Procedures can evolve to incorporate lessonslearne
47、d from previous experience.9.2.3.2 Personnel designing and performing holdup mea-surements must have adequate training, education, and expe-rience. Definition of adequate training, educations, and expe-rience can be found in Guide C1490. Development ofmeasurement plans, strategy and work instruction
48、s and per-forming the initial measurements generally require much moreexpertise than the repeating of routine or subsequent re-measurements. Routine or subsequent remeasurements can beperformed by trained personnel using established proceduresand software.9.2.4 Safety ConditionsEvaluation and mitiga
49、tion of ra-diological and industrial safety issues must be performed priorto initiating measurements.9.2.5 Facility EvaluationThe objective of the evaluationis to develop a measurement plan. Each assay situation isunique. Information must be gathered and evaluated concern-ing the item or items to be assayed, as well as, concerning thelevel of effort necessary to obtain the required level of qualityand precision for the assays.9.2.5.1 Inspect the equipment to be assayed and the sur-rounding area to gain an overview of the task at hand. Considermeasurement geomet
