1、Designation: C 1344 97 (Reapproved 2008)1Standard Test Method forIsotopic Analysis of Uranium Hexafluoride by Single-Standard Gas Source Mass Spectrometer Method1This standard is issued under the fixed designation C 1344; the number immediately following the designation indicates the year oforiginal
2、 adoption or, in the 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.1NOTESection reference in Section 9.2 was corrected editorially in March 2009.1
3、. Scope1.1 This test method covers the isotopic analysis of uraniumhexafluoride (UF6) and may be used for the entire range of235U isotopic compositions for which standards are available.1.2 This test method is applicable to the determination ofthe isotopic relationship between two UF6samples. If the
4、abundance of a specific isotope of one sample (the standard) isknown, its abundance in the other can be determined. This testmethod is flexible in that the number of times a given materialis admitted to the ion source may be adjusted to the minimumrequired for a specified precision level.1.3 The sen
5、sitivity with which differences between twomaterials can be detected depends on the measuring systemused, but ratio-measuring devices can generally read ratio-of-mol ratio differences as small as 0.0001.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement ar
6、e included in thisstandard.1.5 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 practices and determine the applica-bility of regulatory limitations p
7、rior to use. Specific hazardsstatements are given in Section 7.2. Referenced Documents2.1 ASTM Standards:2C 787 Specification for Uranium Hexafluoride for Enrich-mentC 996 Specification for Uranium Hexafluoride Enriched toLess Than 5 %235U2.2 Other Document:USEC-651, Uranium Hexafluoride: A Manual o
8、f GoodHandling Practices33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 drop through, na measurement of the amount of the238UF5+ion beam that can be passed through the235UF5+collector slit and measured on the235UF5+collector, stated asa percentage of the total238UF5+signal.3.
9、1.2 memory corrections, ncorrections applied to thesample analysis results for memory effects.3.1.3 memory effect, nthe inability of the mass spectrom-eter to omit completely the isotopic composition of the sampleanalyzed previously from attributing to the results of furthersamples analyzed.3.1.4 no
10、rmal isotopic abundance material, nUF6having avalue of 0.711 weight percent (wt %)235U.3.1.5 ratio-of-mol-ratios, nthe mol ratio (235U/238U) ofthe sample divided by the mol ratio of the standard, or theinverse condition of the mol ratio of the standard divided by themol ratio of the sample.4. Summar
11、y of Test Method4.1 Test MethodThe unknown sample and a standard withan isotopic composition close to that of the sample areintroduced in sequence into the Neir mass spectrometer. UF5+ions of the isotopes are focused through a mass-resolvingcollector slit and onto a faraday cup collector. Measuremen
12、tsare made of235UF5+to the total of the other UF5+isotopes.With the known composition of the standard, calculation of the235U composition of the sample can be determined.5. Significance and Use5.1 Uranium hexafluoride is a basic material used to preparenuclear reactor fuel. To be suitable for this p
13、urpose, the1This test method is under the jurisdiction ofASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved Dec. 1, 2008. Published January 2009. Originallyapproved in 1997. Last previous edition approved in 2003
14、 as C 1344 97 (2003).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. Enrichment Corporat
15、ion, 6903 Rockledge Dr., Bethesda,MD 20817, http:/.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.material must meet the criteria for isotopic composition. Thistest method is designed to determine whether the materialmeets the requi
16、rements described in Specifications C 787 andC 996.5.2 ASTM Committee C-26 Safeguards Statement:5.2.1 The material (uranium hexafluoride) to which this testmethod applies is subject to the nuclear safeguards regulationsgoverning its possession and use. The analytical procedure inthis test method has
17、 been designated as technically acceptablefor generating safeguards accountability data.5.2.2 When used in conjunction with appropriate certifiedreference materials (CRMs), this procedure can demonstratetraceability to the national measurement base. However, adher-ence to this procedure does not aut
18、omatically guarantee regu-latory acceptance of the regulatory safeguards measurements.It remains the sole responsibility of the user of this test methodto ensure that its application to safeguards has the approval ofthe proper regulatory authorities.6. Apparatus6.1 Neir Mass Spectrometer, with the f
19、ollowing features andcapabilities:6.1.1 A single-focusing spectrometer, with a 127-mm mini-mum deflection radius, is satisfactory when equipped andfocused as follows:6.1.1.1 The sample inlet system must have two sampleholders, to which UF6containers can be attached, and thenecessary valves to evacua
20、te the sample lines through whichthe sample and standard are introduced. The sample inletsystem should be nickel or Monel for use with corrosive gases,and should have minimum volume.6.1.1.2 A single adjustable leak, operated by an automaticleak control mechanism for admitting the sample into thespec
21、trometer ion source, is preferred.6.1.1.3 The pumping system of the spectrometer analyzertube must maintain a pressure below 5 3 108torr with sampleflowing into the ion source.6.1.1.4 Focus the instrument for resolution consistent withprecision requirements. A high-current ion beam of 5 3 1010to 1 3
22、 109amps is necessary, with a signal-to-noise ratiogreater than 3000 in the low-current amplifier system.6.1.1.5 A dual collector must be used, so that ions from oneisotope are passed through a resolving slit and focused on alow-current collector, and ions from all other isotopes arefocused on a hig
23、h-current collector. The preferred method ofmaintaining the low-current ion beam within the collector slitis by an automatic beam positioner circuit.Aresolving slit withadjustable width features enhances the measurement of allisotopes but is not mandatory for isotopic measurements.6.1.1.6 The amplif
24、ied high- and low-current signals are fedinto a multimeter or other device capable of ratioing high- andlow-current signals. If a multimeter is used, the multimetermust have a minimum of 5.5 digits of resolution, a means ofratioing the high- and low-current signals, and interactivecommunication capa
25、bility with the controller.6.1.1.7 The memory effect of the spectrometer must beconsistent with the precision required since a high memorylevel is usually more variable than a low one. Memory valuesof 2 to 3 % are typical, but up to 10 % memory can betolerated. The memory characteristics of a spectr
26、ometer mustbe established from periodic measurement of the effect. Cur-rent memory values usually will apply until the ion source isreplaced, repairs are made on the sample inlet system, or theinstrument is refocused so the flow rate of UF6is alteredsignificantly.6.1.1.8 The computer control of the
27、mass spectrometer mustallow the operator to monitor parameters of the spectrometerand check other operating conditions. The development of aninteractive program allows input of sample information, per-forms necessary calculations, makes memory corrections, andrecords data. Flexibility of the interac
28、tive program allowspausing of the instrument for adjustment or restart capability,or both. Suggested methods of analysis checks include thestandard deviation (SD) on individual data points, linearity ofthe data set, and a check of source pressure differences betweenthe standard and sample that can b
29、e monitored by the computerprogram. Manifold valve actuation, conditioning time, andpump-out time are features of the computer control program.7. Hazards7.1 Since UF6is radioactive, toxic, and highly reactive,especially with reducing substances and moisture (see USEC-651), appropriate facilities and
30、 practices for analysis must beprovided.8. Procedure8.1 Calibration of Isotopic Standards:8.1.1 One working standard is required for the analysis of asample at any specific concentration of any isotope. Twoworking standards are required to determine memory correc-tions. Memory can be measured more p
31、recisely with a largedifference between two working standards, but the adverseeffect of introducing wide concentration ranges into the massspectrometer must be considered. Ideally, the values obtainedfrom the high- and low-memory standards should symmetri-cally bracket those of the sample to be corr
32、ected. Workingstandards approximately 5 % apart (having a ratio of ratios of1.05) are suitable for most applications.8.1.2 A reasonable limit for the relative e between theunknown sample and the working standard to which it iscompared is 2.5 %. A series of working standards prepared at5 % intervals
33、and used for sample comparisons thus enablesthis 2.5 % limit.8.1.3 Prepare a working standard, and standardize againstan oxide blend of CRM standards that is within 0.02 % of thevalue of the working standard.8.2 Sample Preparation:8.2.1 Attach tubes containing the appropriate working stan-dard, S, a
34、nd the sample, X, to the spectrometer inlet system,and prepare the materials for introduction into the ion source,as follows:8.2.1.1 If adequate sample and working standard are avail-able, open all valves between the sample and working standardcontainers and the pumping system, except the valves on
35、thesample and working standard containers. If the amount ofsample or working standard is limited, proceed to 8.2.2.8.2.1.2 Open the valve on the sample container, and thenclose it quickly to vent gases to the pumping system.C 1344 97 (2008)128.2.1.3 After the pumping system has evacuated the ventedg
36、ases, repeat the steps given in 8.2.1.2 a second time.8.2.1.4 Repeat the steps given in 8.2.1.2 and 8.2.1.3 for theworking standard.8.2.2 Use the following alternative method of sample puri-fication if the amount of the sample or working standard islimited:8.2.2.1 Operate the appropriate valves to r
37、emove air en-trapped in the connectors and to determine that there are noleaks into the inlet system.8.2.2.2 Freeze the UF6by immersing the container in amixture of water and ice.8.2.2.3 Open the valve on the container to permit theevacuation of volatile impurities from the container, and thenclose
38、the container valve.8.2.2.4 Remove the coolant from around the container,allowing the UF6to return to room temperature.8.3 Instrument Preparation:8.3.1 Prepare the instrument for analysis as follows:8.3.1.1 Operate the appropriate valves to admit the workingstandard into the ion source.8.3.1.2 With
39、the beam positioner in the manual mode, adjustthe mass spectrometer high-voltage or magnet current to focusthe235UF5+ion beam through the collector slit to the low-current collector, while the other UF5+ions are collected on thehigh-current collector. This peaking up is complete when thecurrent to t
40、he low-current collector is maximized. Place thebeam positioner in the automatic mode.8.3.1.3 Zero both amplifiers as frequently as needed. Somemust be zeroed daily; others may require zeroing only once perweek.8.3.1.4 Adjust the variable leak until the flow of UF6intothe ion source produces a curre
41、nt of approximately 109ampsto the high-current collector. Place the leak control in theautomatic position. If the analyzer pressure is not within2 3 108torr of that observed when the working standard isadmitted as in 8.3.1.1, further purify the UF6having the higherpressure.8.3.1.5 Terminate the flow
42、 of the working standard, andevacuate the ion source.8.3.2 The shortest sequence for the analytical determinationis X, S, X, where X and S represent introductions of the sampleand standard, respectively. Follow each introduction by evacu-ation of the ion source before the next introduction. The timi
43、ngof the introductions and evacuations depends on the instru-ments being used but is typically approximately 2 min forsample introduction followed by a 30-s evacuation. Thenumber of introductions per analytical sequence depends onthe precision required. To minimize errors caused by drift inthe spect
44、rometer, always begin and end the sequence with thesame material in the spectrometer source. A five-introductionsequence (X, S, X, S, X) is most commonly used. An extrapreliminary or equilibration introduction, during which no dataare recorded, precedes the determination to make the sample-standard
45、interaction more uniform and to improve the validityof the memory correction. During each introduction of UF6into the ion source, conduct the following functions eithermanually or automatically:8.3.2.1 Regulate the ion intensity to within 2 % of thedesired level by adjusting the variable leak. This
46、regulationmay be conducted manually or by an automatic leak controlcircuit.8.3.2.2 Adjust the magnet current or high voltage to obtaina maximum low-current collector signal, and maintain at thisvalue for the entire sample introduction period; or repeatedlysweep across this maximum to obtain a series
47、 of scans of thepeak maxima during the period.8.3.2.3 With the instrument peaked up, obtain a readingwith the electrometers for the two collectors connected to amultimeter placed in the ratio circuit position. This reading isproportional to the ratio of the number of ions striking thelow-current col
48、lector over the number of ions striking thehigh-current collector.8.3.3 Average all of the readings for the standard. Alsoaverage all of the readings for the sample. The two values, RXand RS, are calculated for each analytical sequence.8.3.4 Repeat the sequence, as needed, to obtain the desiredanaly
49、tical precision.8.3.5 To correct for memory effects, intersperse memorysequences with sample sequences, using two memory stan-dards that bracket the samples isotopic composition and thatdiffer in isotopic composition by approximately 10 %. Desig-nate the results of RAand RBfor memory standards A and B,respectively. Usually, less than 5 % of the total number ofdeterminations needs and to be made on memory standards.Schedule memory measurements more frequently for maxi-mum precision and plot on a time scale. Interpolate thememory factor from this plot at t
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