The document summarizes research on testing the effects of vibration on used nuclear fuel (SNF) rods using a unique piece of equipment called CIRFT. CIRFT fatigue testing has been conducted on SNF from pressurized water reactors and boiling water reactors. The testing has provided data on the fatigue endurance of the fuel/clad system and shown the SNF to be robust under various loading conditions below the fatigue threshold. Future work will include further data analysis, testing of additional SNF samples, and experiments subjecting the SNF to higher intensity transient loads.

1. Nuclear Energy
CIRFT Testing of High-Burnup Used Nuclear Fuel
from PWRs and BWRs
J.-A. Wang, H. Wang, H. Jiang,
Y. Yan, B. Bevard
Oak Ridge National Laboratory
Used Fuel Disposition Campaign
June 8, 2016
Las Vegas, NV

2. 2
Random vibration provides the external loading
driver to the SNF assemblies; internal vibration
drivers could be transient shocks generated by
basket & spacer grids and fuel rod interactions
Acceleration-time history shows presence of discrete
shock signals superimposed on continuous vibration

3. 3
To investigate the effects of vibration on SNF,
a unique piece of test equipment was designed
and built at ORNL, the Cyclic Integrated
Reversible-Bending Fatigue Tester (CIRFT)

4. 4
CIRFT testing provides important fatigue
endurance information on SNF
 Provides experimental data on fuel/clad system fatigue endurance limits to
support model validation
 Fatigue endurance testing has been conducted on three types of cladding:
• High-burnup pressurized water reactor (PWR) fuel (HB Robinson) – 23
tests
• High-burnup boiling water reactor (BWR) fuel (Limerick) – 15 tests
• AREVA M5™ clad PWR fuel (North Anna & Catawba MOX) – 19 tests
• Testing on sister rods is planned to begin in 2017
 Fuel has performed robustly under various loading conditions and under
millions of vibration cycles below the fatigue threshold loading
• Results are documented in: FY 2015 Status Report: CIRFT Testing of High-
Burnup Used Nuclear Fuel Rods from Pressurized Water Reactor and Boiling
Water Reactor Environments

5. 5
PWR high-burnup SNF rod used for CIRFT
testing reveals good bonding at fuel-clad
interface and the remaining fuel pellet dish
Fuel-clad interface

6. 6
High-burnup HBR PWR SNF fatigue data
show a well-defined S-N curve with
failure at the P-P interface

7. 7
CIRFT fatigue test results reveal some
data scatter due to different types/sizes
and burnup of clads tested
W/ two foot drop
W/ one foot drop

8. 8
CIRFT strain vs. cycles-to-failure
reflects less data scatter taking into
account the clad sizes/types

9. 9
A reduction in cycles-to-failure was noted
when a drop-induced transient shock was
induced
y = 3.5693x-0.252
R² = 0.8722
0.00
0.10
0.20
0.30
0.40
0.50
1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07
StrainAmplitude(%)
Number of Cycles or Cycles to Failure
HBR Failure
HBR, no failure
NA Failure
MOX Failure
NA, no failure
Power (NA Failure)
Power (MOX Failure)
Power (HBR/NRC Failure)
The data point with red arrows represents test data where the sample experienced a
two-foot drop (twice); both MOX specimens were tested with the same dynamic
loading of 5N⋅m.

10. 10
HBR SNF S-N data indicates a hydrogen
content dependency
yLH = 291.5x-0.239
R² = 0.9963
yHL = 324.81x-0.267
R² = 0.8906
0
5
10
15
20
25
30
35
40
1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07
Moment(Nm)
Number of Cycles-to-Failure
Power (H<=550wppm)
Power (H>=700 wppm)
Hydrogen was estimated from oxide thickness; detailed hydrogen
measurements are needed to further quantify any hydrogen-dependent
failure mechanism

11. 11
BWR CIRFT tested specimen failed
at P-P interface
Fracture segments for LMK03/575B-A. (a) and (d) show the specimen ID
side of the test segment; (b) and (e) show the mating fracture surface; and
(c) and (f) show the opposite specimen ID side of the test segment.

12. 12
Hydride reorientation system and
associated equipment for in-cell hydride
reorientation tests have been tested out
of cell and have been moved in cell
• The hydride reorientation test
equipment was constructed and
tested out of cell.
• Planned test temperature: 400°C
• The max. test pressure: 3500 psi
(24MPa)
Tubing weld system with a welded
unirradiated Zry-4 sample
Oxide layer removal device with an oxide
layer removed Zry-4 sample
Furnace
Hydride
reorientation
system
High
pressure
system

13. 13
Out-of-Cell benchmark tests helped
optimize reorientation test parameters
Produced a high ratio of radial hydrides for in-cell hydride reorientation
tests with high-burnup HBR fuel segments.
Test conditions to be used for in-cell testing

14. 14
Three in-cell hydride reorientation
demonstration have been successfully
completed
4”-long HBR fueled
specimen for welding
Micrographs showing (a) circumferential hydrides
before the hydride reorientation test, (b) radial
hydrides after the hydride reorientation test.
• The system was installed in the hot cell.
• All equipment functioned as expected.
– Welder: tested with both unirradiated and irradiated
cladding samples
– High pressure system: tested at 3500 PSI at room
temperature, as well as at elevated temperatures
– Furnace system: tested on an unirradiated sample
overnight
– First in-cell reorientation demonstration
(welding/thermal cycling) was successfully
completed on high burnup SNF at 400°C with a hoop
stress ≈145 MPa (see Slide 12 for details of thermal
cycles).
(a) (b)

15. 15
HR1 break appears to be very different
from the previous (non-reoriented) tests
• Fracture appears to
have initiated at PPI,
however fracture
propagated in sheer
direction.
• Additional cracks and
pellet features can be
seen on sheer lip.

16. 16
Met of HR1 in Longitudinal Direction
De-bonded
fuel-cladding
interface
Bonded fuel-cladding
interface

17. 17
Pellet fragmented – not sure why yet
• Fracture appears to have initiated at PPI. The sheer lip may have ended at the adjacent PPI.
• The pellet in the fracture zone broke into many pieces, however the adjacent pellets appear
largely intact.
• It is difficult to draw any conclusions about the state of the fuel/clad bond from these images.

18. 18
HR3 End View
HR3-A End View HR3-B End View

19. 19
HBR and HR CIRFT Test Results
Load vs. Failure Frequency
y = 270.85x-0.245
R² = 0.8976
0
5
10
15
20
25
30
35
40
1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08
MomentAmplitude(Nm)
Number of Cycles or Cycles to Failure
HBR Failure
HBR No failure
HR
Power (HBR Failure)

20. 20
HBR and HR CIRFT Test Results
Strain vs. Failure Frequency*
y = 3.5693x-0.252
R² = 0.8722
0.00
0.10
0.20
0.30
0.40
0.50
1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08
StrainAmplitude(%)
Number of Cycles or Cycles to Failure
HBR Failure
HBR No failure
HR
Power (HBR Failure)
*HR has much less flexural rigidity compared to that of HBR CIRFT samples

21. 21
Observations from the CIRFT testing:
• Pellet-clad-interaction includes P-C bonding efficiency
• Hydrogen concentration does affect SNF system strength
• The SNF system has significant stress concentrations and
residual stress distributions which can serve to reduce the system
strength
• Pellet-pellet interface
• Pellet-clad bonding
• Hydride distribution
• It appears that transient shock accumulated damage may reduce
the SNF fatigue lifetime

22. 22
Future work will focus on detailed analysis
of experimental data, testing of Sister rods
(with and without heat treatments), and
testing for higher intensity “jolts”
■ Analyze previously obtained experimental SNF test data
• Conduct detailed analyses of CIRFT test results
• Collect and analyze hydride reorientation test results
• Conduct post-irradiation examination (PIE) of hydride reorientation
experiments
■ Sister rod non-destructive tests and destructive tests :