ASTM C1868-18

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: C1868 − 18
Standard Practice for
Ceramographic Preparation of UO and Mixed Oxide
(U,Pu)O Pellets for Microstructural Analysis
This standard is issued under the fixed designation C1868; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 This practice describes the procedure for preparing
1.9 This international standard was developed in accor-
nuclear-grade uranium dioxide (UO ) or mixed uranium-
dance with internationally recognized principles on standard-
plutonium dioxide (MOX or (U,Pu)O )), sintered and non-
ization established in the Decision on Principles for the
irradiated pellets for subsequent microstructural analysis (here-
Development of International Standards, Guides and Recom-
after referred to as ceramographic examination).
mendations issued by the World Trade Organization Technical
1.2 Theceramographicexaminationisperformedtoconfirm
Barriers to Trade (TBT) Committee.
that the microstructure of the sintered pellet is in compliance
2. Referenced Documents
with the fuel specification, for example as defined in Specifi-
cationsC776andC833,asafunctionoftheinitialrawmaterial
2.1 ASTM Standards:
properties and manufacturing process parameters.
C776 Specification for Sintered Uranium Dioxide Pellets for
1.3 The microstructure of a ceramic pellet includes: grain Light Water Reactors
C833 Specification for Sintered (Uranium-Plutonium) Diox-
size, porosity size and distribution, and phase distribution for
(U,Pu)O pellets, that is, Pu-rich cluster size and distribution. ide Pellets for Light Water Reactors
C859 Terminology Relating to Nuclear Materials
1.4 The microstructural characteristics of the pellet are
D1193 Specification for Reagent Water
accessible after preparation which involves: sawing, mounting
E105 Practice for Probability Sampling of Materials
in a resin, surface polishing, and chemical etching, thermal
E112 Test Methods for Determining Average Grain Size
etching, or both.
3. Terminology
1.5 This practice describes the preparation processes men-
tioned in 1.4; it does not discuss the associated sampling
3.1 Except as otherwise defined herein, definitions of terms
practices (for example, Practice E105) or ceramographic ex-
are as given in Terminology C859.
amination methods (for example, the methods for determining
3.2 Definitions of Terms Specific to This Standard:
average grain size are covered in Test Method E112).
3.2.1 grain—single crystal; region of space occupied by a
1.6 Due to the radiotoxicity associated with these nuclear
continuous crystal lattice.
materials, all operations described in this practice should be
3.2.2 microstructure—structure of a material as observed
performed in glovebox for (U,Pu)O pellets and in a hood for
from a magnified view in the range from 0.1 to 100 µm
UO pellets.
involving properties such as grains, grain boundaries, pores,
1.7 The values stated in SI units are to be regarded as
micro-cracks, and phases distribution of the sintered pellet.
standard. No other units of measurement are included in this
3.2.3 MOX—mixed oxide, that is, a blend of uranium and
standard.
plutonium dioxides.
1.8 This standard does not purport to address all of the
3.2.4 porosity—amount of pores (voids) in an object ex-
safety concerns, if any, associated with its use. It is the
pressed as percentage of the total volume.
responsibility of the user of this standard to establish appro-
3.2.5 sintered pellet—densified ceramic compact after heat
treatment at elevated temperatures but below the melting point
This practice is under the jurisdiction of ASTM Committee C26 on Nuclear
of the main component.
Fuel Cycle and is the direct responsibility of Subcommittee C26.05 on Methods of
Test.
Current edition approved Jan. 1, 2018. Published January 2018. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
C1868-18. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
(U,Pu)O fuel pellets are characterized by fissile Pu-rich zones dispersed in a Standards volume information, refer to the standard’s Document Summary page on
fertile depleted UO matrix. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1868 − 18
4. Summary of Practice 4.3.5 Polishing step involves successive stages using in-
creasingly fine grit medium (decreasing in particle size). Each
4.1 Sample Sawing:
stage reduces the scratch sizes generated during the previous
4.1.1 This operation (also called sectioning) is typically
stage.
performed by means of cutting machines equipped with
4.3.6 The fine polished surface should be free of scratches
diamond cut-off wheels.
when viewed by microscope (mirror finish).
4.1.2 The pellet is clamped in a specimen holder which is
4.4 Sample Surface Etching:
placed at the tip of an arm fitted with a counterweight which
4.4.1 Etching is the process to reveal and delineate grain
facilitates adjustment of the penetration force.
boundaries and other microstructural features that are not
4.1.3 The sawing can be done longitudinally or radially. A
visible on the ground and polished surface of the sample.
longitudinal cut is preferable for most applications because it
4.4.2 The polished surface is typically etched by either
permits observation of the pellet structure both along the full
chemical or thermal methods for the purpose of performing
axial length and across the full diameter. Both radial cut and
ceramographic examination as indicated in 1.3.
longitudinal cross-sections together can give information about
4.4.3 Chemical etching consists of submerging the sample
any preferential cracking or agglomerate deformation resulting
in an acid solution (etchant) that will preferentially attack or
from the pelletizing process, the sintering process, or both.
create color-specific phases with different chemical potentials.
4.1.4 Water, emulsions, aqueous solutions, or low-viscosity
The advantages of this method are that it is simple and fast and
mineral oils can be used as a coolant for the cut-off wheels and
can reveal phase distribution; the disadvantage is that it
as a lubricant to minimize any potential mechanical damage of
involves management of contaminated acid wastes.
the sample.
4.4.4 Thermal treatment consists of heating the polished
4.2 Sample Mounting:
sample in a furnace to reveal the surface features by promoting
4.2.1 This operation (also called embedding) is typically
the diffusional, material transport mechanisms (such as surface
performed by immersing the sectioned pellet in a resin which
diffusion, volume diffusion, and evaporation-condensation).
is subsequently hardened by polymerization so as to obtain a
The advantage of this method is that it provides high resolu-
block that is easier to handle during the polishing process.
tion; the disadvantages are that it is time consuming, requires
4.2.2 While this operation can be performed in a hot
a furnace rated for nuclear material (for example, in a
mounting machine under hot compression (150 to 190°C), it is
glovebox), and cannot reveal phase distribution.
preferable to perform manually in a glovebox (cold mounting)
4.5 Sample Cleaning:
sincetheassociatedmountingmediaincludeepoxies,polyester
4.5.1 The sample should be cleaned (for example, in an
resins(thermosets),oracrylates(thermoplastics)whichallcure
ultrasonic cleaner) after sawing step and each polishing stage.
exothermically when mixed with hardeners and catalysts.
4.2.3 In the case of highly porous pellets (with large closed
5. Significance and Use
pores or significant open porosity), the exposed pores create
5.1 The ceramographic examination of the nuclear fuel
potential initiation points for surface damage during polishing
caused by pull-outs. Because of this, it is preferable to perform pellet is mandatory to ensure that the microstructural charac-
teristics are in compliance with the fuel specifications relative
sample mounting in a vacuum mounting chamber by sample
impregnation with high fluidity resin. to performance in reactor, particularly concerning thermo-
mechanical behavior and fission gas release.
4.3 Sample Polishing:
5.2 This practice is applicable for sintered UO pellets with
4.3.1 Rough and fine polishing are the mechanical abrasion
any U concentration and (U,Pu)O pellets containing up to
processes performed on the sample in order to obtain a flat, 2
15 weight % PuO with less than 10 % porosity.
scratch-free surface with minimum mechanical damage (with
the end goal of obtaining a mirror finish).
6. Apparatus and Materials
4.3.2 The rough polishing process consists of flattening the
sample surface and removing the saw marks by the application
6.1 Cutting Machine, for sawing the sample; power-driven
of pressure with a coarse-grit medium (for example, large
diamond wheel with adjustable speed and force; protective
abrasive particles) bonded to adhesive paper or a metal disc.
transparent hood; cooling system for the cutting device and
4.3.3 The fine polishing process consists of removing the
sample; adjustable specimen holder for radial or longitudinal
scratches created by the rough polishing process by the pellet sectioning (and possibly embedded pellet).
application of pressure with a free, fine-grit medium (for
example, a loose collection of small particles such as diamond
oralumina)incorporatedintoapasteorsuspensionspreadonto
a cloth.
4.3.4 Each of the polishing processes uses a fluid which acts
both as a lubricant and as a cooling agent.
When the sample is very brittle (that is, it cracks easily) or highly porous, it is FIG. 1 Mounted Sample (Sectioned Pellet) for Ceramographic
recommended that it be mounted by vacuum impregnation before the sawing step. Examination
C1868 − 18
6.2 Mounting Molds—Adapted to the pellet dimensions and 7.6 Deionized Water (DIW), for lubrication and cooling
polishing head design. during sawing and polishing processes; for rinsing and clean-
ing of sample surface.
6.3 Polishing Machine, for rough and fine polishing the
surface of the sample; rotating disk supporting abrasive media 7.7 Resin, for mounting of the sample; acrylic, polyester or
(for rough polishing) or cloth (for fine polishing); the lubricant
epoxy, acid resistant.
or abrasive solution are manually or automatically applied to
7.8 Abrasive Paste or Suspension, for fine polishing of the
the media at a controlled flow rate. Polishing can be performed
sample.
manually (one sample at a time) or automatically via polishing
head (multiple samples) with controlled, constant pressure
8. Precautions
applied to the mounted samples.
8.1 Because of the nuclear toxicity, all operations should be
6.4 Abrasive Media, for rough polishing the surface of the
performedwithinanapprovedgloveboxorhoodequippedwith
sample; silicon carbide (SiC) or diamond particles bonded to
appropriate filters and negative pressure to capture any small
paper or a grinding disc; the medium is usually stated with a
nuclear particles.
grit size number that is inversely proportional to the abrasive
8.2 Any personnel involved with this procedure must be
particle size.
familiar with safe handling practices for radiologically con-
6.5 Polishing Cloth, for fine polishing the sample; nap or
trolled materials, as well as working in glovebox.
napless, natural or synthetic.
8.3 Use extreme caution when operating the cutting ma-
6.6 Ultrasonic Cleaner, for cleaning of the sample.
chine and polishing machine.
6.7 Digital Microscope or Optical Microscope with CCD
8.4 Use tongs for manipulating the sample in the ultrasonic
(Charge Coupled Device) Camera, for exporting the image to
cleaner.
a computer located outside the glovebox.
8.5 Use caution when handling the liquid nitrogen.
6.8 Hotplate, for heating of etching solution, un-mounting
8.6 Use appropriate precautions
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