1、Designation: C 1344 97 (Reapproved 2003)Standard 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the isotopic analysis of uraniumhexafluorid
3、e (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 theabundance of a specific isotope of one sample (the standard) isknown, its abun
4、dance 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 sensitivity with which differences between twomaterials can be detected depends o
5、n 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 as thestandard. The values given in parentheses are for informationonly.1.5 This standard does not purport to address all
6、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 prior to use. Specific hazardsstatements are given in Section 7.2. Referenced
7、Documents2.1 ASTM Standards:C 787 Specification for Uranium Hexafluoride for Enrich-ment2C 996 Specification for Uranium Hexafluoride Enriched toLess Than 5 %235U22.2 Other Document:USEC-651, Uranium Hexafluoride: A Manual of GoodHandling Practices33. Terminology3.1 Definitions of Terms Specific to
8、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.3.1.2 memory corrections, ncorrections applied to thesample analysis results f
9、or 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 normal isotopic abundance material, nUF6having avalue of 0.711 weight percent
10、(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. Summary of Test Method4.1 Test MethodThe unknown sample and a standard withan isot
11、opic 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. Measurementsare made of235UF5+to the total of the other UF5+isotopes.With the known co
12、mposition 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 purpose, thematerial must meet the criteria for isotopic composition. Thistes
13、t method is designed to determine whether the materialmeets the requirements 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 it
14、s possession and use. The analytical procedure in1This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved Aug. 10, 1997. Published May 1997.2Annual Book of ASTM Standards,
15、 Vol 12.01.3Available from U.S. Enrichment Corporation, 6903 Rockledge Dr., Bethesda,MD 20817.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.this test method has been designated as technically acceptablefor generating safeguards acc
16、ountability 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 automatically guarantee regu-latory acceptance of the regulatory safeguard
17、s 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 following features andcapabilities:6.1.1 A single-focusing spectrometer,
18、 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 evacuate the sample lines through whichthe sample and standard are introduced
19、. 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 thespectrometer ion source, is preferred.6.1.1.3 The pumping system of the spe
20、ctrometer 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 109amps is necessary, with a signal-to-noise ratiogreater than 3000 in
21、 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 high-current collector. The preferred method ofmaintaining the low-current
22、 ion beam within the collector slitis by an automatic beam positioner circuit. A resolving slit withadjustable width features enhances the measurement of allisotopes but is not mandatory for isotopic measurements.6.1.1.6 The amplified high- and low-current signals are fedinto a multimeter or other d
23、evice 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 capability with the controller.6.1.1.7 The memory effect of the spectrome
24、ter 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 spectrometer mustbe established from periodic measurement of the effect. Cu
25、r-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 mass spectrometer mustallow the operator to monitor parameters of the
26、 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 interactive program allowspausing of the instrument for adjustment or restar
27、t 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 be monitored by the computerprogram. Manifold valve actuation, conditi
28、oning 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 practices for analysis must beprovided.8. Procedure8.1 Calibration o
29、f 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 precisely with a largedifference between two working standards, but th
30、e 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 corrected. Workingstandards approximately 5 % apart (having a ratio of ra
31、tios 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 and used for sample comparisons thus enablesthis 2.5 % limit.8.1.3 Pr
32、epare 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, and the sample, X, to the spectrometer inlet system,and prepare the ma
33、terials 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 thesample and working standard containers. If the amount ofsample or
34、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.8.2.1.3 After the pumping system has evacuated the ventedgases, repeat the steps given in 8.2.1.2 a second time.8.2.1.4 Repeat the steps given in
35、 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:C 1344 97 (2003)28.2.2.1 Operate the appropriate valves to remove air en-trapped in the connectors and to determine that there are
36、 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 the container valve.8.2.2.4 Remove the coolant from around the contain
37、er,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 the beam positioner in the manual mode, adjustthe mass spectrometer hi
38、gh-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 the low-current collector is maximized. Place thebeam positioner in the
39、 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 current of approximately 109ampsto the high-current collector. Place the le
40、ak 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 of the working standard, andevacuate the ion source.8.3.2 The shortes
41、t 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 timingof the introductions and evacuations depends on the instru-ments bei
42、ng 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 spectrometer, always begin and end the sequence with thesame material in th
43、e 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 interaction more uniform and to improve the validityof the memory corre
44、ction. 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 regulationmay be conducted manually or by an automatic leak controlcirc
45、uit.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 of scans of thepeak maxima during the period.8.3.2.3 With the instrume
46、nt 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 collector over the number of ions striking thehigh-current collector.8.3.3
47、 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 desiredanalytical precision.8.3.5 To correct for memory effects, intersperse memory
48、sequences 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 ofdetermina
49、tions 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 the time a sample is analyzed.9. Calculation9.1 Percent Drop ThroughA convenient method for de-termining ion beam resolution is to measure the “drop through”of the238UF5+ion peak. Adjust the high voltage to bring the238UF5peak onto the low-current collector, and then observethe amount signal remaining on the high-current collector.With normal isotopic abundance material, the drop throughsho
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