1. Distributions of fission products on PCI in spent PWR fuels using EPMA
IAEA-CN-178/08-05
Distributions of fission products on PCI in spent PWR fuels using EPMA
International Conference on Management
of Spent Fuel from Nuclear Power Reactors
Yang-Hong Jung
Republic of Korea Energy Research Institute

2. Contents Introduction Sample preparation Result and discussion
Samples- 62,000 MWd/tU - at an average oxygen content region
Samples- 62,000 MWd/tU –at an oxygen rich region
Samples- 53,000 MWd/tU –failed fuel
X-ray mapping image of CRUD sampling from 62,000 MWd/tU
CRUD sampling from failed fuel using cross-section clad
Conclusions

3. Introduction
The failed spent fuel rod with 53,000 MWd/tU and normal spent fuel rod with 62,000 MWd/tU from nuclear power plant were characterized to
compare and observe fission products in fuel-clad gap region by EPMA.
Several recent studies have been conducted on fuel rod failures involving PCI (Pellet-Clad Interaction)
The results from these studies have established that PCI failures are due to SCC(Stress Corrosion Cracking of the cladding)
So, In this study we try to identified a number of fission products (I, Cs, Cd, Xe, Kr) distribution at fuel-clad gab.
The results of this study can be used in the interim dry cask storage facilities for spent fuels which are being used in the Republic of Korea nuclear power plants.
EPMA technique offers the possibility of identifying and analyzing fission products in spent PWR fuel, although the small amounts expected to be present, and the background radiation, present a significant analytical challenge.

4. Experimental and Results
Sample preparation
A thin diamond wheel was cut off from PWR fuel rod.
The sample have been embedded in conducting resin and polished with
diamond paste of 1 ㎛ as a final stage.
The Electron Probe Micro-Analysis(EPMA, SX-50R, CAMECA, France)
technique offers the possibility of identification and analyzing fission products.
Fuel rod
Chopping
Pellet removal
by drilling
Cladding profile
with parts of pellet
Mounting & Polishing
Schematic drawing of the sample preparation

5. Experimental and Results
Sample preparation
The failed spent fuel rod with 53,000 MWd/tU and normal spent fuel rod with
62,000 MWd/tU from nuclear power plant were discharged and cooled down
for 2 and 4 years, respectively.
Normal spent fuel 62,000 MWd/tU
Failed spent fuel 53,000 MWd/tU

6. Experimental and Results
Samples- 62,000 MWd/tU - at an average oxygen content region
An optical microscopy and SEM image of the 62,000 MWd/tU fuel rod
at an average oxygen content region
The concentration of O, Zr, U on the marked point is illustrating the
general trend for release and redistribution in fuel-clad gap region.
The quantitative line scan data taken from across fuel-clad gab shows
stable stats at an average oxygen region.
20㎛

7. Experimental and Results
Samples- 62,000 MWd/tU –at an oxygen rich content region
An optical microscopy, SEM and BSE image of the 62,000 MWd/tU
fuel rod at an oxygen content rich region .
Quantitative analyses of O, Zr, U on the marked point .
20㎛

8. Experimental and Results
Samples- 62,000 MWd/tU –at an oxygen rich content region
The quantitative line scan data of O, Zr, U taken from across fuel-clad gap
shows stable states at an oxygen rich region.
The quantitative line scan data of fission products Cs, Ce, Ba, Sr, I taken from
marked point.
These results means, even at a high burn-up stat in the 62 GWd/tU,
the fuel-clad gab reliability seems to be appropriate conditions.

9. Experimental and Results
Samples- 62,000 MWd/tU –at an oxygen rich content region
The Iodine and tellurium profiles exhibit stable states at an average oxygen
content region .
But, tellurium profiles changed dynamically increased at an rich oxygen
Fuel
Clad

10. Experimental and Results
Samples- 62,000 MWd/tU
The gaseous cesium and xenon distribution are not so dynamically changed
between fuel-clad gap at an average oxygen region of 62,000 MWd/tU fuel rod
Cerium and oxygen distribution are illustrating the general trend for release and
redistribution in fuel-clad gap region.
Qualitative concentration profile of Ce, O along the clad-fuel gap
Qualitative concentration profile of Cs, Xe along the clad-fuel gap
Fuel
Clad
O-Profile
6 ㎛

11. Experimental and Results
Samples- 62,000 MWd/tU –at an oxygen rich content region
The gaseous cesium and xenon distribution are not so dynamically changed
between fuel-clad gap at an oxygen rich region of 62,000 MWd/tU fuel rod
The qualitative concentration profile along the clad-fuel gab obtained by
EPMA to conform the reliability of fission products behaviors at high burn up
fuel conditions and compare with at an average oxygen region and higher
oxygen region.
Clad
Fuel
Qualitative concentration profile of Cs, Xe along the clad-fuel gap
O-Profile
20 ㎛
Qualitative concentration profile of Ce, O along the clad-fuel gap

12. Experimental and Results
Samples- 62,000 MWd/tU - at an average oxygen content region
Xenon and cesium are fission products which are release from the central
parts of the pellet
However, Xenon and oxygen concentration profiles illustrate the general trend
for release and cesium redistribution in fuel-clad gab. Cs U O
20㎛ Xe Zr I
Image mapping of Xe, Zr, O, U,Cs I on the fuel-clad gap

13. Experimental and Results
Samples- 62,000 MWd/tU –at an oxygen rich content region
X-ray image of Xe, Zr, O, U, Cs, I
The concentration of oxygen X-ray image is quietly different from at an
average oxygen content region O Cs U Zr Xe
20㎛ I
Image mapping of Xe, Zr, O, U, Cs, I on the fuel-clad gap

14. Experimental and Results-CRUD
Activated corrosion products, CRUD (Chalk River Unidentified Deposits) from BWR and PWR reactors deposit primarily on the outer surface of fuel rod.
On these surface, the deposits can lead to fuel rod failures and cladding breaches.
Also, it can become detached in cooling water and storage systems, causing additional radiation exposure to plant workers.
Zircalloy cladding is known to have a strong affinity for oxygen.
In –reactor corrosion of the cladding typically produces a thin outer layer of oxide 8-40 ㎛ in thickness.
These deposits are distinguishable from oxide corrosion products dissolved from structural material and piping which are transported into the core from the primary coolant

15. Experimental and Results
Samples- 62,000 MWd/tU
Image mapping of O, Fe on the CRUD
SEM, BSE, X-ray image of CRUD sampling from 6200 MWd/tU SE
10㎛
BSE
20㎛
100㎛ O
50㎛ Fe

16. Experimental and Results
IAEA-CN-178/08-05
Experimental and Results
Samples- 53,000 MWd/tU –failed spent fuel
CRUD sampling from failed fuel using cross-section clad
Quantitative Analysis points O
10㎛ C B Fe Zr
Image mapping of Zr, B,O, Fe, C on the fuel-clad gap

17. Experimental and Results
Samples- 53,000 MWd/tU –failed spent fuel
EPMA quantitative analysis results were executed by dividing parts of crud
that was 8 ㎛ thick into 16 equal points
These result was similar to Trevorite (NiFe2O4) is well known of crud main
compositions. Fe O Ni
100
70.044
Total
0.013
0.01
0.018 Zn
2.917
16.127
1.177
18.651
0.008
0.004
0.006 Co
2.258
28.614
6.676
32.454
0.154
0.507
0.141
0.547 Mn
0.406
0.718
0.189
0.693 Cr
3.708
54.021
4.25
17.68
dev
average
Atomic %
Weight %
NiFe2O3.x
16 point quantitative analysis on crud region

18. Experimental and Results
Samples- 53,000 MWd/tU –failed spent fuel
X-ray image of Zr, O, U of the spent failed fuel rod with 53,000 MWd/tU
The quantitative data of fission products taken from marked point
The thickness of oxidation region was 13 ㎛ and metallic precipitates of Fe and
Sn were found. but the amounts were too low to be considered. Zr O U O
20㎛ U
Image mapping of Zr, O, U on the fuel-clad gap

19. Experimental and Results
Samples- 53,000 MWd/tU –failed spent fuel
Distributions of fission products in PCI region. 25 beam points were set up.
Point numbers from 1-18 points were placed on cladding side.
High concentration of fission products was observed from points
but Cs and Sr were observed over 1.0 wt %. It is almost same results of
Restani. He used SIMS and found that Sr and Cs were observed 1.2 wt%
and 1.0 wt% far from UO2 pellet by fission recoil.

20. Conclusions
The spent failed fuel rod with 53,000 MWd/tU and normal spent fuel rod with
62,000 MWd/tU from nuclear power plant were characterized to compare and
observe fission products on the fuel-clad gap using EPMA.
The gaseous cesium and xenon distribution are not so dynamically changed
between fuel-clad gap at an average oxygen region of 62,000 MWd/tU fuel rod,
quantitative line scan data illustrate the general trend of release and
cesium redistribution in fuel-clad gap region.
Oxygen concentration profile at an average region is about less than 6 ㎛
compare to 20 ㎛ at higher oxygen region between clad to fuel gap. Tellurium
profiles changed dynamically increased at an oxygen rich content region.
Oxide thickness is 13 ㎛ on the PCI region and the contents of the oxide layer
were 34 at.% of zirconium and 66.7 at.% of oxygen respectively in the failed
spent fuel rod with 53,000 MWd/tU.
The results of this study can be used in the interim dry cask storage facilities for
spent fuels which are being used in the Republic of Korea nuclear power plants.

21. Thank you