1、Designation: C 993 97 (Reapproved 2003)Standard Guide forIn-Plant Performance Evaluation of Automatic PedestrianSNM Monitors1This standard is issued under the fixed designation C 993; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision,
2、 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 guide is affiliated with Guide C 1112 on applyingspecial nuclear material (SNM) monitors, Guide C 1
3、169 onlaboratory performance evaluation, Guide C 1189 on calibrat-ing pedestrian SNM monitors, and Guides C 1236 and C 1237on in-plant evaluation. This guide to in-plant performanceevaluation is a comparatively rapid way to verify whether apedestrian SNM monitor performs as expected for detectingSNM
4、 or SNM-like test sources.1.1.1 In-plant performance evaluation should not be con-fused with the simple daily functional test recommended inGuide C 1112. In-plant performance evaluation takes place lessoften than daily tests, usually at intervals ranging from weeklyto once every three months. In-pla
5、nt evaluations are also moreextensive than daily tests and may examine both a monitorsnuisance alarm record and its detection sensitivity for aparticular SNM or alternative test source.1.1.2 In-plant performance evaluation also should not beconfused with laboratory performance evaluation. In-plantev
6、aluation is comparatively rapid, takes place in the monitorsroutine operating environment, and its results are limited toverifying that a monitor is operating as expected, or todisclosing that it is not and needs repair or recalibration.1.2 In-plant evaluation is one part of a program to keepSNM mon
7、itors in proper operating condition. Every monitor ina facility is evaluated. There are two applications of thein-plant evaluation: one used during routine operation andanother used after calibration.1.2.1 Routine Operational EvaluationIn this form of theevaluation, nuisance alarm records for each m
8、onitor are exam-ined, and each monitors detection sensitivity is estimatedduring routine operation. The routine operational evaluation isintended to reassure the plant operator, and his regulatoryagency, that the monitor is performing as expected duringroutine operation. This evaluation takes place
9、without pre-testing, recalibration, or other activity that might change themonitors operation, and the evaluation simulates the normaluse of the monitor.1.2.2 Post-Calibration EvaluationThis form of the evalu-ation is part of a maintenance procedure; it should alwaysfollow scheduled monitor recalibr
10、ation, or recalibration con-nected with repair or relocation of the monitor, to verify that anexpected detection sensitivity is achieved. Nuisance alarm datado not apply in this case because the monitor has just beenrecalibrated. Also, having just been calibrated, the monitor islikely to be operatin
11、g at its best, which may be somewhat betterthan its routine operation.1.3 The values stated in SI units are to be regarded asstandard.1.4 This standard does not purport to address the safetyproblems, if any, associated with its use. It is the responsibilityof the user of this standard to establish a
12、ppropriate safety andhealth practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 The guide is based on ASTM standards that describeapplication and evaluation of SNM monitors, as well astechnical publications that describe aspects of SNM monitorde
13、sign and use.2.2 ASTM Standards:C 859 Terminology Relating to Nuclear Materials2C 1112 Guide for Application of Radiation Monitors to theControl and Physical Security of Special Nuclear Material2C 1169 Guide for Laboratory Evaluation of Automatic Pe-destrian SNM Monitor Performance2C 1189 Guide to P
14、rocedures for Calibrating AutomaticPedestrian SNM Monitors2C 1236 Guide for InPlant Performance Evaluation of Au-tomatic Vehicle SNM Monitors2C 1237 Guide to InPlant Performance Evaluation of Hand-Held SNM Monitors21This guide is under the jurisdiction of ASTM Committee C26 on Nuclear FuelCycle and
15、is the direct responsibility of Subcommittee C26.12 on SafeguardApplications.Current edition approved May 10, 1997. Published May 1998. Originallyapproved in 1991. Last previous edition approved in 1997 as C 993 97.2Annual Book of ASTM Standards, Vol 12.01.1Copyright ASTM International, 100 Barr Har
16、bor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3. Terminology3.1 Definitions:3.1.1 alternative test sourcealthough no other radioactivematerials individually or collectively duplicate the radioactiveemissions of uranium or plutonium, some materials havesomewhat similar attri
17、butes and are sometimes used as alter-native test sources.3.1.2 alternative gamma-ray test sourcesexamples of al-ternative gamma-ray sources are HEU or133Ba used in place ofplutonium when a plutonium source is not readily available oris prohibited.3.1.2.1 DiscussionTable 1 tabulates amounts of HEUma
18、ss, plutonium mass, and133Ba source activity that produceequal response in two different types of monitor.3.1.3 alternative neutron test sourcea common alternativeneutron source used in place of plutonium is252Cf that emitsneutrons from spontaneous fission as does plutonium.3.1.3.1 DiscussionAlterna
19、tive test sources may have shortdecay half-lives in comparison to SNM isotopes; for example,the half-life of133Ba is 10.7 years and252Cf 2.64 years. Largersource activities than initially needed are often purchased toobtain a longer working lifetime for the source.3.1.4 confidence coeffcientthe theo
20、retical proportion ofconfidence intervals from an infinite number of repetitions ofan evaluation that would contain the true result.3.1.4.1 DiscussionIn a demonstration, if the true resultwere known the theoretical confidence coefficient would be theapproximate proportion of confidence intervals, fr
21、om a largenumber of repetitions of an evaluation, that contain the trueresult. Typical confidence coefficients are 0.90, 0.95 and 0.99.3.1.5 Confidence Interval for a Detection ProbabilityAninterval, based on an actual evaluation situation, so constructedthat it contains the (true) detection probabi
22、lity with a statedconfidence.3.1.5.1 DiscussionConfidence is often expressed as 100*the confidence coefficient. Thus, typical confidence levels are90, 95 and 99 %.3.1.6 detection probabilitythe proportion of passages forwhich the monitor is expected to alarm during passages of aparticular test sourc
23、e.3.1.6.1 DiscussionAlthough probabilities are properly ex-pressed as proportions, performance requirements for detectionprobability in regulatory guidance have sometimes been ex-pressed in percentage. In that case, the detection probability asa proportion can be obtained by dividing the percentage
24、by100.3.1.7 nuisance alarma monitoring alarm not caused bySNM but by other causes, such as statistical variation in themeasurement process, a background intensity variation, or anequipment malfunction.3.1.8 process-SNM test sourcean SNM test source fabri-cated by a facility from process material tha
25、t differs in physicalor isotopic form from the material recommended in 3.1.11 forstandard test sources.3.1.8.1 DiscussionThis type of source is used when itmeets plant operator or regulatory agency performance require-ments and a suitable standard source is not readily available.Encapsulation and fi
26、ltering should follow that recommended in3.1.11.3.1.9 SNMspecial nuclear material: plutonium of anyisotopic composition,233U, or enriched uranium as defined inTerminology C 859.3.1.9.1 DiscussionThis term is used here to describe bothSNM and strategic SNM, which includes plutonium,233U, anduranium e
27、nriched to 20 % or more in the235U isotope.3.1.10 SNM monitorradiation detection system that mea-sures ambient radiation intensity, determines an alarm thresh-old from the result, and then, when it monitors, sounds analarm if its measured radiation intensity exceeds the threshold.3.1.11 standard SNM
28、 test sourcea metallic sphere or cubeof SNM having maximum self attenuation of its emittedradiation and an isotopic composition listed below that mini-mizes the intensity of its radiation emission. Encapsulation andfiltering also affect radiation intensity, and particular details arelisted for each
29、source. This type of test source is used inlaboratory evaluation but, if suitable and readily available, maybe used for in-plant evaluation.3.1.12 standard plutonium test sourcea metallic sphere orcube of low-burnup plutonium containing at least 93 %239Pu,less than 6.5 %240Pu, and less than 0.5 % im
30、purities.3.1.12.1 DiscussionA cadmium filter can reduce the im-pact of241Am, a plutonium decay product that will slowlybuild up in time and emit increasing amounts of 60-keVradiation. Begin use of a 0.04-cm thick cadmium filter whenthree or more years have elapsed since separation of plutoniumdecay
31、products. If ten or more years have elapsed sinceseparation, use a cadmium filter 0.08 cm thick. The protectiveencapsulation should be in as many layers as local rulesrequire. A nonradioactive encapsulation material, such as,aluminum (#0.32 cm-thick) or thin (#0.16 cm-thick) stainlesssteel or nickel
32、, should be used to reduce unnecessary radiationabsorption.3.1.13 standard uranium test sourcea metallic sphere orcube of highly enriched uranium (HEU) containing at least93 %235U and less than 0.25 % impurities. Protective encap-sulation should be thin plastic or thin aluminum (#0.32 cmthick) to re
33、duce unnecessary radiation absorption in the encap-sulation. No additional filter is needed.3.2 Definitions of Terms Specific to This Standard:3.2.1 post-calibration evaluationverifies performance af-ter repair, relocation, or recalibration. Monitor is prepared forTABLE 1 Alternative Test Source Equ
34、ivalent AmountsAMonitorCategoryMonitorDescriptionPlutonium,gUranium,g133Ba (Ci)Required inNaI(T1)ScintillatorMonitorsPlasticScintillatorMonitorsI Standard plutonium 1 64 2.5 3.2II Standard uranium 0.29 10 0.9 1.4III Improved sensitivity 0.08 3 0.4 0.6IV High sensitivity 0.03 1 0.2 0.3AThis table com
35、bines information from Tables II and V of the report referencedin Footnote 8. Note that the term “category” refers to an SNM monitor performancecategory used in that report and not to an SNM accountability category. Also notethat the133Ba source strengths depend on individual differences in how thes
36、cintillators respond to radiation from the barium isotope and plutonium.C 993 97 (2003)2best operation. Monitor is not yet in routine operation. Onlysensitivity is evaluated.3.2.2 routine-operational evaluationverifies performancein routine operation. Simulates normal use of a monitor. Usesno monito
37、r preparation procedures. Both sensitivity and nui-sance alarm probability or rate are evaluated.4. Summary of Guide4.1 Preliminary Steps Common to Both Forms of In-PlantEvaluation:4.1.1 The monitor being evaluated is an automaticwalkthrough-portal or monitoring booth.4.1.2 The monitors indicated ba
38、ckground measurementvalue is recorded for possible future use in troubleshooting.4.1.3 Nonmandatory InformationIf a gamma-ray surveymeter (see 6.1) capable of quickly and precisely measuringenvironmental gamma-ray intensity is available, its use andrecording its measurement value may provide additio
39、nal ben-eficial information for future troubleshooting.3Independentknowledge of the ambient background intensity also can helpto interpret performance differences at different monitor loca-tions or at one location at different times.4.2 Steps for Routine Operational Evaluation:4.2.1 Determine nuisan
40、ce alarm probability during the pe-riod since the monitor was last maintained, calibrated, orevaluated (see 8.1). Use recorded numbers of alarms andpedestrian passages from records kept during routine monitoruse.4.2.1.1 Handwritten alarm logs or records from the moni-tors control unit can provide to
41、tal alarms (see Section 6) fromwhich alarms from daily or other performance testing andalarms explained by radioactive material presence in follow-upsearches must be subtracted.4.2.1.2 Total pedestrian passages can be estimated fromoperating logs or recorded information from the monitorscontrol unit
42、.4.2.2 Estimate detection probability by transporting a stan-dard SNM, process-SNM, or alternative test source (seeSection 7) through the monitor in a specific way adopted forevaluation beforehand (see 8.2).4.2.2.1 Record the results, detect or miss for each passage.4.2.2.2 End testing when a total
43、number of passages, se-lected beforehand, is reached.4.2.2.3 Analyze the results as a binomial experiment (see8.2).4.3 Steps for Post-Calibration Evaluation:4.3.1 Calibrate the monitor according to procedures sug-gested by the manufacturer, Guide C 1189, or local practice.4.3.2 Estimate detection pr
44、obability by transporting a stan-dard SNM, process-SNM, or alternative test source (seeSection 7) through the monitor in a specific way adoptedbeforehand (see 8.2).4.3.2.1 Record the results, detect or miss for each passage.4.3.2.2 End testing when a total number of passages, se-lected beforehand, i
45、s reached.4.3.2.3 Analyze the results as a binomial experiment (see8.2).5. Significance and Use5.1 SNM monitors are an effective and unobtrusive meansto search pedestrians for concealed SNM. Facility securityplans use SNM monitors as one means to prevent theft orunauthorized removal of designated qu
46、antities of SNM fromaccess areas. Daily testing of the monitors with radioactivesources guarantees only the continuity of alarm circuits. Thein-plant evaluation is a way to estimate whether an acceptablelevel of performance for detecting chosen quantities of SNM isobtained from a monitor in routine
47、service or after repair orcalibration.5.2 The evaluation verifies acceptable performance or dis-closes faults in hardware or calibration.5.3 The evaluation uses test sources shielded only bynormal source filters and encapsulation and, perhaps, byintervening portions of the transporting individuals b
48、ody. Thetransporting individual also provides another form of shieldingwhen the body intercepts environmental radiation that wouldotherwise reach the monitors detectors. Hence, transportingindividuals play an important role in the evaluation by repro-ducing an important condition of routine operatio
49、n.5.4 The evaluation, when applied as a routine-operationalevaluation, provides evidence for continued compliance withthe performance goals of security plans or regulatory guidance.It is the responsibility of the users of this evaluation tocoordinate its application with the appropriate regulatoryauthority so that mutually agreeable evaluation frequency, testsources, way of transporting the test source, number oftest-source passages, and nuisance-alarm-rate goals are used.Agreed written procedures should be used to document thecoordination.6. App
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