1、Designation: C1868 18Standard Practice forCeramographic Preparation of UO2and Mixed Oxide(U,Pu)O2Pellets for Microstructural Analysis1This standard is issued under the fixed designation C1868; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、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 describes the procedure for preparingnuclear-grade uranium dioxide (UO2) or mixed
3、uranium-plutonium dioxide (MOX or (U,Pu)O2), sintered and non-irradiated pellets for subsequent microstructural analysis (here-after referred to as ceramographic examination).1.2 The ceramographic examination is performed to confirmthat the microstructure of the sintered pellet is in compliancewith
4、the fuel specification, for example as defined in Specifi-cations C776 and C833, as a function of the initial raw materialproperties and manufacturing process parameters.1.3 The microstructure of a ceramic pellet includes: grainsize, porosity size and distribution, and phase distribution for(U,Pu)O2
5、pellets, that is, Pu-rich cluster size and distribution.21.4 The microstructural characteristics of the pellet areaccessible after preparation which involves: sawing, mountingin a resin, surface polishing, and chemical etching, thermaletching, or both.1.5 This practice describes the preparation proc
6、esses men-tioned in 1.4; it does not discuss the associated samplingpractices (for example, Practice E105) or ceramographic ex-amination methods (for example, the methods for determiningaverage grain size are covered in Test Method E112).1.6 Due to the radiotoxicity associated with these nuclearmate
7、rials, all operations described in this practice should beperformed in glovebox for (U,Pu)O2pellets and in a hood forUO2pellets.1.7 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.8 This standard does not purport to address al
8、l of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.9 This international standard was developed i
9、n accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2
10、.1 ASTM Standards:3C776 Specification for Sintered Uranium Dioxide Pellets forLight Water ReactorsC833 Specification for Sintered (Uranium-Plutonium) Diox-ide Pellets for Light Water ReactorsC859 Terminology Relating to Nuclear MaterialsD1193 Specification for Reagent WaterE105 Practice for Probabil
11、ity Sampling of MaterialsE112 Test Methods for Determining Average Grain Size3. Terminology3.1 Except as otherwise defined herein, definitions of termsare as given in Terminology C859.3.2 Definitions of Terms Specific to This Standard:3.2.1 grainsingle crystal; region of space occupied by acontinuou
12、s crystal lattice.3.2.2 microstructurestructure of a material as observedfrom a magnified view in the range from 0.1 to 100 minvolving properties such as grains, grain boundaries, pores,micro-cracks, and phases distribution of the sintered pellet.3.2.3 MOXmixed oxide, that is, a blend of uranium and
13、plutonium dioxides.3.2.4 porosityamount of pores (voids) in an object ex-pressed as percentage of the total volume.3.2.5 sintered pelletdensified ceramic compact after heattreatment at elevated temperatures but below the melting pointof the main component.1This practice is under the jurisdiction of
14、ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods ofTest.Current edition approved Jan. 1, 2018. Published January 2018. DOI: 10.1520/C1868-18.2(U,Pu)O2fuel pellets are characterized by fissile Pu-rich zones dispersed in afertile depleted UO2ma
15、trix.3For 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.Copyright ASTM International, 100 Barr Harbor Drive, PO
16、Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by
17、 the World Trade Organization Technical Barriers to Trade (TBT) Committee.14. Summary of Practice4.1 Sample Sawing:4.1.1 This operation (also called sectioning) is typicallyperformed by means of cutting machines equipped withdiamond cut-off wheels.4.1.2 The pellet is clamped in a specimen holder whi
18、ch isplaced at the tip of an arm fitted with a counterweight whichfacilitates adjustment of the penetration force.4.1.3 The sawing can be done longitudinally or radially. Alongitudinal cut is preferable for most applications because itpermits observation of the pellet structure both along the fullax
19、ial length and across the full diameter. Both radial cut andlongitudinal cross-sections together can give information aboutany preferential cracking or agglomerate deformation resultingfrom the pelletizing process, the sintering process, or both.4.1.4 Water, emulsions, aqueous solutions, or low-visc
20、ositymineral oils can be used as a coolant for the cut-off wheels andas a lubricant to minimize any potential mechanical damage ofthe sample.4.2 Sample Mounting:4.2.1 This operation (also called embedding) is typicallyperformed by immersing the sectioned pellet in a resin whichis subsequently harden
21、ed by polymerization so as to obtain ablock that is easier to handle during the polishing process.4.2.2 While this operation can be performed in a hotmounting machine under hot compression (150 to 190C), it ispreferable to perform manually in a glovebox (cold mounting)since the associated mounting m
22、edia include epoxies, polyesterresins (thermosets), or acrylates (thermoplastics) which all cureexothermically when mixed with hardeners and catalysts.4.2.3 In the case of highly porous pellets (with large closedpores or significant open porosity), the exposed pores createpotential initiation points
23、 for surface damage during polishingcaused by pull-outs. Because of this, it is preferable to performsample mounting in a vacuum mounting chamber by sampleimpregnation with high fluidity resin.44.3 Sample Polishing:4.3.1 Rough and fine polishing are the mechanical abrasionprocesses performed on the
24、sample in order to obtain a flat,scratch-free surface with minimum mechanical damage (withthe end goal of obtaining a mirror finish).4.3.2 The rough polishing process consists of flattening thesample surface and removing the saw marks by the applicationof pressure with a coarse-grit medium (for exam
25、ple, largeabrasive particles) bonded to adhesive paper or a metal disc.4.3.3 The fine polishing process consists of removing thescratches created by the rough polishing process by theapplication of pressure with a free, fine-grit medium (forexample, a loose collection of small particles such as diam
26、ondor alumina) incorporated into a paste or suspension spread ontoa cloth.4.3.4 Each of the polishing processes uses a fluid which actsboth as a lubricant and as a cooling agent.4.3.5 Polishing step involves successive stages using in-creasingly fine grit medium (decreasing in particle size). Eachst
27、age reduces the scratch sizes generated during the previousstage.4.3.6 The fine polished surface should be free of scratcheswhen viewed by microscope (mirror finish).4.4 Sample Surface Etching:4.4.1 Etching is the process to reveal and delineate grainboundaries and other microstructural features tha
28、t are notvisible on the ground and polished surface of the sample.4.4.2 The polished surface is typically etched by eitherchemical or thermal methods for the purpose of performingceramographic examination as indicated in 1.3.4.4.3 Chemical etching consists of submerging the samplein an acid solution
29、 (etchant) that will preferentially attack orcreate color-specific phases with different chemical potentials.The advantages of this method are that it is simple and fast andcan reveal phase distribution; the disadvantage is that itinvolves management of contaminated acid wastes.4.4.4 Thermal treatme
30、nt consists of heating the polishedsample in a furnace to reveal the surface features by promotingthe diffusional, material transport mechanisms (such as surfacediffusion, volume diffusion, and evaporation-condensation).The advantage of this method is that it provides high resolu-tion; the disadvant
31、ages are that it is time consuming, requiresa furnace rated for nuclear material (for example, in aglovebox), and cannot reveal phase distribution.4.5 Sample Cleaning:4.5.1 The sample should be cleaned (for example, in anultrasonic cleaner) after sawing step and each polishing stage.5. Significance
32、and Use5.1 The ceramographic examination of the nuclear fuelpellet is mandatory to ensure that the microstructural charac-teristics are in compliance with the fuel specifications relativeto performance in reactor, particularly concerning thermo-mechanical behavior and fission gas release.5.2 This pr
33、actice is applicable for sintered UO2pellets withany235U concentration and (U,Pu)O2pellets containing up to15 weight % PuO2with less than 10 % porosity.6. Apparatus and Materials6.1 Cutting Machine, for sawing the sample; power-drivendiamond wheel with adjustable speed and force; protectivetranspare
34、nt hood; cooling system for the cutting device andsample; adjustable specimen holder for radial or longitudinalpellet sectioning (and possibly embedded pellet).4When the sample is very brittle (that is, it cracks easily) or highly porous, it isrecommended that it be mounted by vacuum impregnation be
35、fore the sawing step.FIG. 1 Mounted Sample (Sectioned Pellet) for CeramographicExaminationC1868 1826.2 Mounting MoldsAdapted to the pellet dimensions andpolishing head design.6.3 Polishing Machine, for rough and fine polishing thesurface of the sample; rotating disk supporting abrasive media(for rou
36、gh polishing) or cloth (for fine polishing); the lubricantor abrasive solution are manually or automatically applied tothe media at a controlled flow rate. Polishing can be performedmanually (one sample at a time) or automatically via polishinghead (multiple samples) with controlled, constant pressu
37、reapplied to the mounted samples.6.4 Abrasive Media, for rough polishing the surface of thesample; silicon carbide (SiC) or diamond particles bonded topaper5or a grinding disc; the medium is usually stated with agrit size number that is inversely proportional to the abrasiveparticle size.6.5 Polishi
38、ng Cloth, for fine polishing the sample; nap ornapless, natural or synthetic.6.6 Ultrasonic Cleaner, for cleaning of the sample.6.7 Digital Microscope or Optical Microscope with CCD(Charge Coupled Device) Camera, for exporting the image toa computer located outside the glovebox.6.8 Hotplate, for hea
39、ting of etching solution, un-mountingof sample (that is, removing sample from mold), or both; acidresistant.6.9 Furnace, for thermal treatment of sample; operationtemperature in the range of 1300 to 1700C, and thermal inertiaas low as possible (high heating rate).6.10 Lab Glassware, for preparation
40、of etching solution.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are avail
41、able.6Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the reliability ofthe ceramographic preparation.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent wat
42、er as definedby Type IV of Specification D1193.7.3 Acids, for chemical etching; hydrofluoric acid (HF),sulfuric acid (H2SO4), nitric acid (HNO3), chromic acid(H2CrO4).7.4 Oxidants, for chemical etching; hydrogen peroxide(H2O2), chromium oxide (Cr2O3).7.5 Liquid Nitrogen (N2), for un-mounting of the
43、sample.7.6 Deionized Water (DIW), for lubrication and coolingduring sawing and polishing processes; for rinsing and clean-ing of sample surface.7.7 Resin, for mounting of the sample; acrylic, polyester orepoxy, acid resistant.7.8 Abrasive Paste or Suspension, for fine polishing of thesample.8. Preca
44、utions8.1 Because of the nuclear toxicity, all operations should beperformed within an approved glovebox or hood equipped withappropriate filters and negative pressure to capture any smallnuclear particles.8.2 Any personnel involved with this procedure must befamiliar with safe handling practices fo
45、r radiologically con-trolled materials, as well as working in glovebox.8.3 Use extreme caution when operating the cutting ma-chine and polishing machine.8.4 Use tongs for manipulating the sample in the ultrasoniccleaner.8.5 Use caution when handling the liquid nitrogen.8.6 Use appropriate precaution
46、s for handling hazardousmaterials (for example, appropriate gloves).8.7 Comply with the safety recommendations relative to theheating equipment (for example, hot plate, furnace, etc.).8.8 Hydrofluoric acid is a highly corrosive acid that canseverely burn skin, eyes, and mucous membranes. Hydroflu-or
47、ic acid differs from other acids because the fluoride ionreadily penetrates the skin, causing destruction of deep tissuelayers. Unlike other acids that are rapidly neutralized, hydro-fluoric acid reactions with tissue may continue for days if leftuntreated. Familiarization and compliance with the Sa
48、fety DataSheet is essential.9. Procedure9.1 Sample Sawing:9.1.1 Place the pellet in the specimen holder of the cuttingmachine, oriented longitudinally or radially. It is recommendedto adjust the position of the specimen holder so that the pelletcan be cut along the central axis in order to obtain th
49、e largestcross-section possible.9.1.2 Supply cooling and lubricant liquid.9.1.3 Start the cutting machine. The counter-mass and speedare adjusted to facilitate slow, continuous cutting.9.1.4 After cutting, rinse the two sample sections in anultrasonic cleaner and dry.9.2 Sample Mounting:9.2.1 Prepare the resin in accordance with the manufactur-ers instructions ensuring that there are no residual bubblesafter the mixing step (resin and hardener).9.2.2 Place the sample section into a mold cup (sectionedsurface facing down in the bottom).9.2.3 Pour the resin onto the sample
