1、Designation: C 1703 08Standard Practice forSampling of Gaseous Uranium Hexafluoride1This standard is issued under the fixed designation C 1703; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
2、parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers methods for withdrawing represen-tative sample(s) of uranium hexafluoride (UF6) during atransfer occurring in the gas phase.
3、 Such transfer in the gasphase can take place from a mother cylinder, for example in anautoclave to a receiving cylinder. It can also occur during thefilling in the gas phase of a cylinder during a continuousproduction process, for example centrifuge enrichment facilityor the distillation column in
4、a conversion facility. Suchsample(s) may be used for determining compliance with theapplicable commercial specification, for example SpecificationC 996 or Specification C 787.1.2 Since UF6sampling is taken during the filling process,this practice does not address any special additional arrange-ments
5、 that may be agreed upon between the buyer and theseller when the sampled bulk material is being added toresidues already present in a container (“heels recycle”). Sucharrangements will be based on QA procedures such as trace-ability of cylinder origin (to prevent for example contaminationwith irrad
6、iated material).1.3 If the receiving cylinder is purged after filling andsampling, special verifications must be performed by the userto verify the representativity of the sample(s). It is thenexpected that the results found on volatile impurities with gasphase sampling may be conservative.1.4 This
7、practice is only applicable when the transfer occursin the gas phase. When the transfer is performed in the liquidphase, Practice C 1052 should apply. This practice does notapply to gas sampling after the cylinder has been filled sincethe sample taken will not be representative of the cylinder.1.5 T
8、he scope of this practice does not include provisionsfor preventing criticality incidents.1.6 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 practic
9、es and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 761 Test Methods for Chemical, Mass Spectrometric,Spectrochemical, Nuclear, and Radiochemical Analysis ofUranium HexafluorideC 787 Specification for Uranium Hexafluoride for Enrich
10、-mentC 996 Specification for Uranium Hexafluoride Enriched toLess Than 5 %235UC 1052 Practice for Bulk Sampling of Liquid UraniumHexafluoride2.2 Other Document:ISO/DIS 7195 Packaging of Uranium Hexafluoride (UF6)for Transport33. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 con
11、tainera vessel either holding or receiving bytransfer, the UF6to be sampled; it may consist of, for example,a fixed vessel in a UF6handling plant or a cylinder to be usedfor the transport of UF6.3.1.2 sample vesselthe small vessel into which the sampleof UF6is withdrawn for analysis in the laborator
12、y for charac-terization. It can be a 1S or 2S bottle or a PCTFE(polydifluorodichloroethylene)/ PTFE (polytetrafluoroethyl-ene) pot or tube or any other type of cylinder compatible withUF6.4. Summary of Practices4.1 Two methods of withdrawing gas UF6for sampling arepossible, namely: (1) continuous wi
13、thdrawal using for examplea capillary and producing only one sample, or (2) sequentialwithdrawals producing a composite sample. Depending on thepressure and temperature conditions during the transfer, thesampled UF6is either liquefied or solidified in the samplevessel.1This practice is under the jur
14、isdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.02 on Fuel andFertile Material Specifications.Current edition approved Dec. 1, 2008. Published December 2008.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM
15、Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1Copyright ASTM Int
16、ernational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 An example of (1) is the sampling of UF6coming froma distillation column. In such case, the sampled gas UF6can becondensed in the liquid phase in the sampling vessel. Therepresentative sample is then
17、homogenized before analysis atthe laboratory. It is assumed that the flow rate from thedistillation is either constant (for example using a mass flowcontroller) or that the capillary will take its variation inaccount.4.3 Examples of (2) are the sampling of UF6from anautoclave or from the cascades of
18、 an enrichment facility. Thiswould apply only to a stable process. In such case, thesequential withdrawals must take into account the potentialvariation of flow rate which must be continuously monitoredduring the transfer. A composite sample is prepared and iscompared to an average calculation using
19、 on line analysis.4.4 For both methods of sampling, the presence of residuesmay have significant implications for the quality of the UF6.For safety and quality reasons, cylinders and bottles shall beclean, dry, and empty before filling.5. Significance and Use5.1 Uranium hexafluoride is normally prod
20、uced and handledin large (typically 1 to 14-ton) quantities and must, therefore,be characterized by reference to representative samples (seeISO/DIS 7195). The samples are used to determine compliancewith the applicable commercial specifications C 996 andC 787. The quantities involved, physical prope
21、rties, chemicalreactivity, and hazardous nature of UF6are such that forrepresentative sampling, specially designed equipment must beused and operated in accordance with the most carefullycontrolled and stringent procedures. This practice can be usedby UF6converters, enrichers, and fuel fabricators t
22、o review theeffectiveness of existing procedures or as a guide to the designof equipment and procedures for future use.5.2 The intention of this practice is to avoid liquid UF6sampling once the cylinder has been filled. For safety reasons,manipulation of large quantities of liquid UF6should beavoide
23、d when possible.5.3 It is emphasized that this practice is not meant to addressconventional or nuclear criticality safety issues.6. Hazards6.1 Because of its chemical, radiochemical, and toxic prop-erties, UF6is a hazardous material.7. Principles7.1 The essential purpose of the sample(s) is to be re
24、pre-sentative of the total material which has been transferred. It isthe responsibility of the user to determine the way of continu-ous sampling or the number of samples and time distributionthat are necessary to be representative, depending on theprocess variability. For example, in case of the pre
25、sence of highlevel of very volatile impurities, additional samples may haveto be taken at the beginning of the transfer.7.1.1 It is recommended to validate the gas sampling usinga comparison on several cylinders with liquid sampling afterfilling. Statistically significant sampling basis and requirem
26、entshould be established. Adequacy shall be demonstrated byquality assurance procedures.7.1.2 In case of the presence of volatile impurities close tothe specification (for example within 80 % of the specifica-tion), a confirmation using liquid sampling may be necessary.7.2 Uranium hexafluoride is ve
27、ry reactive and corrosive. Itreacts readily with water, atmospheric moisture, certain metals,and many organic materials. For reasons of safety and to avoidcontamination, precautions must be taken to avoid contact withsuch materials. The sampling equipment is therefore fabricatedto appropriate high s
28、tandards of vacuum and high temperatureintegrity, and components in direct contact with UF6are madefrom nickel, high-nickel alloys, or materials having equivalentresistance to UF6corrosion. The formation of an inert fluoridelayer is often an important feature of UF6corrosion resistance,and hence, in
29、ternal surfaces are generally conditioned with asuitable fluorinating agent, sometimes UF6itself.7.3 Cross-contamination may occur between subsequentsamples taken using the same equipment, and appropriateprecautions must be taken to prevent this. It is thereforerecommended that, before taking defini
30、tive samples, the equip-ment is flushed through with an aliquot of the material to besampled. This is normally accomplished by taking an initialvolume which is then rejected and not used for definitiveanalysis. Alternative procedures to prevent cross-contamination are possible and should be validate
31、d individu-ally.8. Procedure for Continuous Sampling During Filling ofa Transport Cylinder8.1 Sample Preparation:8.1.1 The equipment consists of a continuous samplingvessel that has the ability to collect a desired weight/volume ofUF6during the filling of a UF6transport cylinder, and a samplemanifol
32、d used for obtaining the aliquot of UF6from thecontinuous sampling vessel. The sampling manifold can be apermanent (fixed) manifold, and can be the same manifoldused for sampling straight from a product cylinder. Thecontinuous sampling vessel should be fed gaseous UF6from aslip stream at the exit of
33、 the supplying source (for example, adistillation column) that is supplying UF6to a transportcylinder.8.1.2 The continuous sampling vessel should be maintainedat a temperature and pressure adequate for condensing andmaintaining UF6in liquid phase, to allow for homogenizationby the action of convecti
34、on currents within the bulk liquid. Thecontinuous sampling vessel should be operated so that acomposite sample of UF6could be withdrawn during the entirefilling cycle of a transport cylinder. The continuous samplingvessel should be able to be isolated from the supply so thatadequate purging of the v
35、essel and supply lines can beaccomplished after the sampling cycle is complete.8.1.3 The continuous sampling vessel should be opened todraw a sample from the UF6feed line at the beginning of fillingof the transport cylinder. At the completion of filling thetransport cylinder the continuous sampler s
36、hould be isolatedfrom the feed line.8.1.4 The sampling manifold should be appropriately sizedto contain the quantity of UF6required for a single sample andnormally, consists of the manifold and associated pipe work ormay also include an additional metering volume (pipette). TheC1703082total graduate
37、d volume of the connected equipment (excludingthe vacuum system) should not exceed the designated maxi-mum fill volume of the attached sample vessels. Certain valvesmay be remotely operated as necessary. The sampling equip-ment should be heated to prevent the solidification of UF6.8.1.5 The weight/v
38、olume of UF6collected in the continuoussampling vessel should be monitored by load cell, so to notoverfill the continuous sampling vessel. This sample volumeshould be adequate for flushing the piping between thecontinuous sampling vessel and the sampling manifold, as wellas the manifold itself. The
39、total volume of the sample manifoldshould be transferred to the sample cylinder without anyventing.8.2 Sampling:8.2.1 The UF6can now be sampled into a desired number ofsample vessels from the continuous sampling vessel.8.2.2 Attach the sample vessel to the sampling manifold (ifa fixed manifold is us
40、ed) or attach the sampling equipment,including sample vessels, at the relevant location on the UF6runoff line from the continuous sampler. Evacuate and test theequipment to ensure vacuum integrity. Isolate the samplevessels from the sample manifold.8.2.3 Open the valves on the continuous sampling ve
41、ssel toallow liquid UF6to flow to the sampling manifold.8.2.4 Establish liquid transfer of UF6from the UF6continu-ous sampling vessel to the sampling manifold.Allow a suitableamount of UF6to flush the sampling manifold and piping fromthe continuous sampler to manifold.8.2.5 At an appropriate time, o
42、pen the valve and withdrawthe required quantity of UF6into the graduated volume. Thismay be indicated by the use of suitable temperature sensors,pressure transducers, strain gauges, a line of sight window atthe top of the transfer pipette, or combinations thereof.8.2.6 Close the manifold valve and o
43、pen the first samplevessel valve to transfer the sample. The equipment should bedesigned to allow transfers to take place using the influence ofgravity and differential pressures induced by temperaturegradients. For this reason, it may be necessary to cool thereceiving vessels.8.2.7 The first sample
44、 may be used to condition internalsurfaces of the equipment by suitable manipulation of thevacuum system or rejected to prevent cross-contaminationfrom earlier materials or both.8.2.8 Isolate the sample vessel from the sampling manifold.8.2.9 If successive samples are to be taken, repeat 8.2.5 and8.
45、2.6.8.2.10 At the completion of sampling, close all the samplevessel valves. Any residual UF6in the equipment, samplinglines, and continuous sampling vessel is withdrawn using drygas or evacuated into a UF6trap. Purge all equipment with drygas several times to assure any residual vapors have beenrem
46、oved.8.2.11 Remove, identify, cap, and weigh the sample vessels.Local safety regulations may demand that the UF6be allowedto cool and solidify before this operation is carried out.9. Procedure for Sequential Sampling9.1 Description of the Main Steps:9.1.1 During cylinder filling, successive gas samp
47、les areisolated in an intermediate dosing vessel. The UF6is each timecollected in the same vessel (CDG or 1S or alternative) whichis maintained at low temperature. The frequency of withdrawalis regular. The number of transfers and the vessel volume aredefined to ensure sufficient material for analyz
48、ing and provid-ing a representative sample.Arepresentative sample is ensuredby withdrawing a quantity which is proportional to the flowrate, an appropriate frequency of withdrawing is used, thepressure is also checked and a cross check with on line analysisis carried out.9.1.2 An on-line235U isotopi
49、c analysis is performed at thesame time; the UF6flow rate and the pressure in the vessel areconstantly monitored. Ti and Qi are the235U content and flowrate found at time i.9.1.3 The235U is measured on the UF6collected in thevessel and then compared to the average calculation usingon-line measurement: STi Qi/ S Qi.9.1.4 If the difference between the two235U values is notsignificant (based for example on a 95 % confidence limit), thestability of the process is considered sufficient and the materialcan be used for further sub-sampling and analysis according toTest Methods C 761 in ord
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