1、Designation: C1455 14Standard 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 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 gamma-ray methods used tonondestructively measure the quantity of
3、235Uor239Pu 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 useful formanagement, planning, selection of equipmen
4、t, 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, transmission of radiation, calibration, facilityopera
5、tions 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 and distribution of the material, various background
6、s,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-tributed in a diffuse and irregular manner. It is di
7、fficult 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 its use. It is theresponsibility of the user of th
8、is 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 ofNondestructive Assay (NDA) PersonnelC1592 Guide for Nondest
9、ructive 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 ofNuclear Material Holdup: General Provisions2.3
10、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 measurements range from thesolitary assay of a sin
11、gle 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 performed in situ onequipment or items instead of
12、on multiple items with similarcharacteristics measured in a specialized, isolated room. Oftenthe chemical form and geometric distribution of the SNM arenot well known. These challenges require unique preparation1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle an
13、d is the 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/C1455-14.2The boldface numbers in parentheses refer to the list of re
14、ferences 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
15、National 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 States1for eve
16、ry 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 objectives (that is, criticality control, SNMaccountabilit
17、y, 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 authorities should agree on the holdup measurementrequirement
18、s 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 measurement requirements.Preliminary measurements may
19、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 configuration of the item orprocess equipment to be assayed, lo
20、cation 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. Sources of information mayinclude a visual survey, engin
21、eering 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 changeshave been made to the process.4.3.2 Shutdown facili
22、ties 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 method, assaymodel, and subsequently leads to determi
23、nation 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 measurementlocations and geometries or guidance for their selec
24、tion. Themeasurement plan will reference overall measurement programdocuments governing required documentation, operatingprocedures, background measurement methods andfrequencies, plus training, quality and measurement controlrequirements. Any needed additional procedures should bedeveloped, documen
25、ted, 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 detailed in the measurement plan or procedure.4.7 Eval
26、uation 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 effects in the assay modeland for self-attenuation.
27、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 careful evaluationof the measurement parameters against
28、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, andinterferences. Measurement uncertainties (random and
29、 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. If a discrepancy is evident, an evaluation should b
30、emade. 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-surement location, the measurement techniques used, the r
31、awdata, 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 assists indemonstrating regulatory compliance in such area
32、s 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 flux generally will cause pulsepileup, which affects
33、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 registered by the equipment. Dead timeindication from the
34、 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 candegrade the energy resolution of the spectra.8.2.3 Secular
35、 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 information to determine ifsecular equilibrium has been
36、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 corrections are notsimple to perform and the measurement
37、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 principles discussed are appli-cable to all measurements.8
38、.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.8.2.5.1 Care must be taken to position the detector
39、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 cause a bias in low resolution measurements. Forexam
40、ple, 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 Measurement Plan,9.1.2 Preparation for Measurements,9.1.3
41、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 (3, 4, 9, 10, 11) NRCRegulatory Guide 5.23).9.2 Proce
42、dureMeasurement 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. The informationshould provide the boundaries for the t
43、ask 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 Acceptable lower detection limit for the assay.9.2.1
44、.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 and reporting require-ments.9.2.2 Resource Constraints:
45、C1455 1449.2.2.1 The time available to perform the measurement(s),analyze the data and report the results.9.2.2.2 Resources available to perform the individual mea-surement or the measurement program.9.2.3 Personnel and ProceduresThere are typically twolevels of procedures: (1) generic or all-encomp
46、assing 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 lessonslearned from previous experience.9.2.3.2 Personnel designing
47、 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 instructions and per-forming the initial measurements generally r
48、equire 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 mitigation of ra-diological and industrial safety issues mus
49、t 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 geometry, other sources of radiation, attenuatingmaterials, and
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