BS ISO 22765:2016 pdf download – Nuclear fuel technology — Sintered (U,Pu)O 2 pellets — Guidance for ceramographic preparation for microstructure examination
8.1 Specimen cutting
The pellet is cut using a diamond-impregnated metallography disk-cutting machine with a coolingsystem, along the selected axis (longitudinal or axial).
After cutting, the specimen is cleaned in alcohol or demineralised water.An ultrasonic cleaning tankmay be used.
Prior to rough and final polishing, the cut specimen is embedded in resin.Therefore, the half pellet isput inside a mould with the cut face against the mould bottom.
The prepared resin, with potentially a colouring in order to distinguish the pellet Pu content, is thenpoured inside the mould.
After the required time (e.g. around 30 min to 60 min), the embedding pellet can be removed fromthe mould.
Then, the identification number of the pellet sample can be graved with the engraver pen on the resin.The mould should be cleaned in order to reuse it.
8.3 Rough polishing
The resin-embedded specimens shall be, at first, rough-polished to eliminate any resin traces on thesurface and ensure flatness. This may be done using a multi-stage process.
An example is described below:
– P180 (82 um) abrasive disk (for specimens embedded in resin after cutting): time as necessary to
reach the surface flush with the resin;
P400 (35 um) abrasive disk: 30 s to 1 min;- P800 (22 um) abrasive disk: 30 s to 1 min;- P1200 (15 um) abrasive disk: 30 s to 1 min;
Rough polishing is performed on a polishing machine with an air pressure of 100kPa to 150kPa, and ata rotation speed of 70 r/min to 270 r/min.
The specimen is thoroughly cleaned in alcohol between each step and after completion of the roughpolishing operation.The cleaning may be done in an ultrasonic tank.
An example is described below.
The polishing operation is performed using a series of woven satin disks after injecting a diamond-paste with a grain size of 1 um to 6 um.Polishing is carried out for about 20 min on a polishing machinewith an air pressure of 100 kPa to 200 kPa.
The specimen is thoroughly cleaned in alcohol and dried in air after polishing.The cleaning may bedone in an ultrasonic tank.The polished surfaces should be mirror finished and free of scratches.
The polishing quality is checked by observing the specimen under a microscope or a binocular.
The pellets prepared in this way are suitable for examinations such as
— porosity measurements, and
— overall ceramographic examinations to reveal cracking.
9 Structure development
To determine the grain size, the structure should first be revealed by thermal treatment or chemical etching. Chemical etching can also be used to reveal the distribution of plutonium clusters. An alternative, to reveal the distribution of plutonium clusters, can be the alpha-autoradiography.
9.2 Development by thermal treatment
After cutting, the sample is not embedded, but placed into a mechanical device. Then, the half pellet placed in the mechanical device is polished. The polishing operation prior to the thermal treatment may be done using a multi-stage process.
An example is described below.
Rough polishing is performed on a polishing machine with an air pressure of 100 kPa to 150 kPa, and at
a rotation speed of 70 r/min to 270 r/min.
— P180 (82 μm) abrasive disk (for specimens embedded in resin after cutting): time as necessary to reach the surface flush with the resin
— P400 (35 μm) abrasive disk: 30 s to 1 min
— P800 (22 μm) abrasive disk: 30 s to 1 min
— P1200 (15 μm) abrasive disk: 30 s to 1 min
The specimen is thoroughly cleaned (ultrasonically or not) in alcohol between each step and after completion of the rough polishing operation.
Final polishing (see 8.4)
The sample is introduced into the furnace after dismounting from the mechanical device.
Thermal treatment can be carried out under various conditions. An example is described below:
— heating rate: 283 °C/h;
— fixed temperature level: 1 600 °C;
— duration: 6 h;
— scavenging with argon throughout the cycle.BS ISO 22765 pdf download.