1、Designation: C1817 16Standard Test Method forThe Determination of the Oxygen to Metal (O/M) Ratio inSintered Mixed Oxide (U, Pu)O2) Pellets by Gravimetry1This standard is issued under the fixed designation C1817; the number immediately following the designation indicates the year oforiginal adoption
2、 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.1. Scope1.1 This practice is an alternative method to Test MethodC698 for the determinat
3、ion of the oxygen-to-metal atom ratio(O/M) in sintered mixed oxide fuel (MOX) pellets. The methodpresented in Test Method C698 is a one-step thermogravimet-ric method for determining O/M ratio in sintered MOXpowders and pellets. As stated in Test Method C698, thermo-gravimetric methods using a two-s
4、tep heating cycle are alsosatisfactory (1, 2).2The method presented in this test method isa two-step heating cycle method. This test method is applicableto sintered MOX pellets containing up to 10 weight percentPuO2.1.2 The values stated in SI units are to be regarded asstandard. No other units of m
5、easurement are included in thisstandard.1.3 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
6、limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C698 Test Methods for Chemical, Mass Spectrometric, andSpectrochemical Analysis of Nuclear-Grade Mixed Ox-ides (U, Pu)O2)C753 Specification for Nuclear-Grade, Sinterable UraniumDioxide PowderC757 Specification for Nuclear-Grade Plut
7、onium DioxidePowder, SinterableC833 Specification for Sintered (Uranium-Plutonium) Diox-ide PelletsC859 Terminology Relating to Nuclear MaterialsC1068 Guide for Qualification of Measurement Methods bya Laboratory Within the Nuclear IndustryC1672 Test Method for Determination of Uranium or Pluto-nium
8、 Isotopic Composition or Concentration by the TotalEvaporation Method Using a Thermal Ionization MassSpectrometerD1193 Specification for Reagent WaterD1356 Terminology Relating to Sampling and Analysis ofAtmospheres2.2 ISO Standards:4ISO 21484 Nuclear Fuel Technology Determination of theO/M Ratio in
9、 MOX Pellets Gravimetric Method FirstEdition3. Terminology3.1 For definitions of terms used in this test method but notdefined herein, refer to Terminology C859.3.2 Definitions of Terms Specific to This Standard:3.2.1 average of the relative atomic massthe weightedaverage of the relative atomic mass
10、 of an element calculated asa function of its isotopic composition.3.2.2 mole fractionthe ratio of the number of molecules(or moles) of a compound or element to the total number ofmolecules (or moles) present (Terminology D1356).3.2.3 MOXnuclear fuel composed of a mixture of uraniumand plutonium oxi
11、des (U, Pu)O2).3.2.4 O/Mratio of the oxygen atoms divided by the metalatoms in the sample.3.2.5 relative atomic massa dimensionless physicalquantity, the ratio of the average mass of atoms of an element(from a single given sample or source) to112 of the mass of anatom of carbon-12 (known as the unif
12、ied atomic mass unit).3.2.6 scavengingthe process of pushing a gas out byintroducing a fresh flow in.1This 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 Jan. 15, 2016
13、. Published February 2016. Originallyapproved in 2015. Last previous edition approved in 2015 as C1817 15. DOI:10.1520/C1817-16.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontac
14、t 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 International Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:
15、/www.iso.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.7 sinteringto increase the bonding in a mass of pow-der or a compact by heating below the melting point of themain constituent.4. Summary of Test Method4.1 The purpose o
16、f the analysis is to test the stoichiometryof the MOX pellet by the determination of the O/M ratio. Theprinciple of the method is that one or a number of MOX pelletsare heated under a specific set of atmospheric conditions inorder to add or subtract oxygen molecules to the MOX pellets.This process r
17、esults in an O/M ratio of 2 in the MOX pelletsafter heating. The mass of the oxygen molecules added to orsubtracted from the MOX pellets to achieve an O/M ratio of 2is quantified by weighing the MOX pellets before and after theheating step. Once the difference in mass is known, the numberof atoms of
18、 oxygen added to or subtracted from the MOXpellets can be determined. The resulting data are used tocalculate the O/M ratio in the pellets prior to heating.4.2 Three or four MOX pellets are weighed before and afteran oxidation-reduction heat treatment at specified time andtemperature intervals.4.3 T
19、he heating and atmospheric conditions required toachieve an O/M ratio of 2 in the MOX pellets are as follows(3-5):(1) Oxidation of the pellets in a current of air at 900 620C to increase the O/M ratio. There is no evidence thatoxygen can be absorbed interstitially by plutonium dioxide toproduce hype
20、rstoichiometric oxide containing plutonium ionshaving a valency higher than four. On the contrary, uraniumoxide can be hyperstoichiometric.(2) Reduction of the pellets in a stream of argon/hydrogengas at 900 6 20C to reduce the O/M ratio to 2. Under theseconditions (temperature and reducing atmosphe
21、re), the O/Mratio is adjusted to 2. The choice of these parameters is basedupon a compromise between selecting a temperature lowenough to prevent reduction of plutonium oxide to a hypostoi-chiometric state but high enough to reduce hyperstoichiometricuranium oxide to UO2.NOTE 1The O/M ratio increase
22、s during the cooling process after theheat cycles described above unless it is done under Ar or Ar/H2atmosphere. So, control of the cooling atmosphere is needed.4.4 The reactions involved are:U , Pu!O26x6x2O2U , Pu!O21x(1)U , Pu!O21x1xH2U , Pu!O2.0001xH2O (2)4.5 The calculation of the stoichiometry
23、is based on theweight difference of the pellets before and after heat treatmentand the mean atomic mass of the heavy metals in the MOXpellets (see Section 11 for details of the calculation).5. Significance and Use5.1 MOX is used as a nuclear-reactor fuel. This test methodis designed to determine whe
24、ther the O/M ratio meets therequirements of the fuel specification. Examples for establish-ing a fuel specification are given in Specification C833.5.2 This method is suitable for all sintered MOX pelletscontaining up to 12 weight % PuO2when the UO2and PuO2meet the requirements of Specifications C75
25、3 and C757.6. Interferences6.1 Impurities in the sample may lead to inaccuracies in thedetermination of O/M ratios either due to loss of volatiles orgain due to redox reactions. Even inert impurities present insufficiently high amounts compromise the accuracy of O/Mratios because the true mass of th
26、e (U, Pu)O2) subjected to theoxidation-reduction process remains unknown. When purifiedPuO2and UO2powders with maximum total impurity contentsspecified in Specifications C753 and C757 are used, the changein mass due to the non-volatile and volatile impurities isinsignificant to the method. This meth
27、od assumes that therequirements of these two standards are met and therefore doesnot take into account the impact of impurities. If impuritycontents are higher than those specified in Specifications C753and C757, an evaluation should be performed to determinetheir impact on the method. This test met
28、hod assumes thatpellets are sintered. It does not correct for moisture or volatileadditives as the content of these impurities is negligible aftersintering.6.2 The crucibles if not clean can be a potential interference.If necessary, the crucibles are cleaned and fired before use asdescribed in 10.1.
29、 If crucible cleanliness is tracked and ifcrucibles are cleaned when necessary, the potential for thecrucibles to be a source of interference is insignificant.6.3 If crucibles are made from materials that oxidize underthe test conditions, they may prevent proper equilibration ofthe stoichiometry of
30、the sample by consuming availableoxygen. In addition, they would change weight and wouldimpact the difference in mass calculation. This method assumesthat the crucible is made out of a material that is inert under thetest conditions, such as platinum alloyed with 20 % rhodium.6.4 Weighing accuracy o
31、f the samples is critical to themethod. If the balance meets the specification in 7.1,iscalibrated in accordance with manufacturers guidance, and ischecked by procedure, the potential for the balance to be asource of error is insignificant.6.5 Loss of weight due to pellet chipping would invalidateth
32、e analysis. Handle pellets with care.6.6 The average of the relative atomic mass of the uraniumand plutonium in the samples impacts the accuracy of thecalculation. The average of the relative atomic mass of uraniumand plutonium are measured by Thermal Ionization MassSpectrometry (TIMS) in accordance
33、 with Test Method C1672and this measured value is accounted for in the calculation.7. Apparatus7.1 Analytical Balance, with precision 60.1 mg.7.2 Tube Furnace, capable of controlling temperatures 9006 20C and fitted with a fused quartz tube chamber whichallows for sweeping the chamber with various g
34、asses.7.3 O/M ApparatusSee Fig. 1. This apparatus is nottypically commercially available and users of this test methodmust build a similar device.NOTE 2It is important that the thermocouple be located such that itcan monitor the temperature in the zone in which the sample is placed, orcan be calibra
35、ted to account for any physical offset. It is also importantC1817 162that the furnace is designed so that the temperature remains stable acrossthe region in which the sample is placed. For safety reasons, it is importantto ensure that the design of the furnace limits the possibility of mixing airwit
36、h the hydrogen/argon gas mixture.7.4 Platinum sample cruciblesalloyed with 20 % rho-dium.7.5 Fused Quartz Boats (if needed), designed to holdmultiple platinum sample crucibles if more than one sample ismeasured at the same time.7.6 Pair of Stainless Steel Tweezers.7.7 Pair of Tongs (if using cleanin
37、g method 2 described in10.1).7.8 Hot Plate (if using cleaning method 2 described in10.1).7.9 Beaker (if using cleaning method 2 described in 10.1).7.10 Gas Flow Meter, Pressure Gauge, and Regulator.8. Reagents and Materials8.1 Purge Gases:8.1.1 ArgonCertified 99.995 % purity (O25 mg.kg-1,H2O 5 mg.kg
38、-1,N220 mg.kg-1).8.1.1.1 Flow rate: 16 litres/hour.8.1.1.2 Pressure: 200 kPa.8.1.2 AirFiltered and dried (Suggested air treatment sys-tem features: filter efficiency 98 % of 0.01 m, dew point20C, total hydrocarbons 5 mg.m-3).8.1.2.1 Flow rate: 12 litres/hour.8.1.2.2 Pressure: 200 kPa.8.1.3 Argon/Hyd
39、rogen MixtureCertified 99.995 % puritywith the total amount of impurities (O2+H2O+CnHm) 10mg.kg-1. The gas mixture shall be (5 % H27 %).8.1.3.1 Flow rate: 16 litres/hour.8.1.3.2 Pressure: 200 kPa.8.2 Liquid Reagents:8.2.1 Water (if using cleaning method 2)Unless otherwiseindicated, references to wat
40、er shall be understood to meanlaboratory accepted demineralized or deionized water in con-formance with Specification D1193, Type 1.8.2.2 Nitric Acid (if using cleaning method 2)(16 MHNO3) concentrated, specific gravity 1.42.8.2.3 Nitric Acid 7M (if using cleaning method 2)Add 440mL of concentrated
41、HNO3to 900 mL of DI water, dilute to afinal volume of 1 litre.8.3 Reference Materials:8.3.1 There are no certified reference materials (MOXpellets) for the O/M ratio determination by the thermogravi-metric treatment method (6).9. Precautions9.1 Because of the toxicity of plutonium, all operationssho
42、uld be performed within an approved glove box fitted withappropriate filters to contain any small particle of plutonium.Adetailed discussion of the necessary precautions is beyond thescope of this test method. Personnel involved in these analysesshould be familiar with safe handling practices (7, 8)
43、.9.2 The furnace, sample tube, and sample crucibles areheated to 900 6 20C. Extreme care must be exercised to avoidburns or injury by quartz in a glove box and to avoid breachingthe primary confinement boundary.9.3 Exercise appropriate caution when working with com-pressed gases.FIG. 1 O/M Apparatus
44、C1817 1639.4 Hydrogen is explosive when mixed with oxygen in thepresence of an ignition source. Using a mixture of argon andhydrogen instead of pure hydrogen, limiting the hydrogencontent to a maximum of 7 % and ensuring that the design ofthe furnace does not allow for the hydrogen/argon mixture tor
45、eact with air limits the safety risk of this method. Using aglove box with an inert atmosphere also reduces the risk andimproves the method performance.10. Procedure10.1 Crucible CleaningThe crucibles shall be clean andweighed before use. Cleaning prior to each use is not required,but an evaluation
46、of the cleanliness of the crucible is required.Cleaning is required if dust is visible. If crucible cleaning isdeemed required, the following are two examples of how thecrucibles can be cleaned.10.1.1 Example Cleaning Method 1:10.1.1.1 Wipe out the empty crucible with disposable paperor cotton wipes
47、.10.1.1.2 Introduce the crucible (crucibles in the quartz boatif necessary) into the furnace using a pair of tweezers and sealthe furnace door.10.1.1.3 Place the furnace under argon/hydrogen by intro-ducing the argon/hydrogen at a pressure of 200 kPa, and a flowrate of 16 L/h.10.1.1.4 Turn on the fu
48、rnace.10.1.1.5 Heat the crucibles at 900 6 20C for 1 h.10.1.1.6 Shut off the furnace and allow the crucible to coolto less than 150C in the argon-hydrogen atmosphere withinthe furnace. If the glove box atmosphere is inert, the cruciblescan be removed at a higher temperature.10.1.1.7 Remove the cruci
49、bles (crucibles in the quartz boatif necessary) from the furnace using a pair of tweezers, shut offthe argon-hydrogen and allow the crucibles to cool to less than35C.10.1.1.8 Weigh each crucible to within 60.1 mg. Record thevalue as m0.10.1.2 Example Cleaning Method 2:10.1.2.1 Wipe out the empty crucible with disposable paperor cotton wipes.10.1.2.2 Place the crucibles in a beaker with enough 7MHNO3to completely cover the crucibles.10.1.2.3 Place the beaker containing the crucibles onto a hotplate and boil the acid for approximatel
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