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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
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
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
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
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
High-burnup HBR PWR SNF fatigue data
show a well-defined S-N curve with failure at the P-P interface
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
CIRFT strain vs. cycles-to-failure reflects less data scatter taking into
account the clad sizes/types
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
Stra
in A
mpl
itude
(%
)
Number of Cycles or Cycles to Failure
HBR FailureHBR, no failureNA FailureMOX FailureNA, no failurePower (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
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
Mom
ent (
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
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
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
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
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
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
Met of HR1 in Longitudinal Direction
De-bonded fuel-cladding interface
Bonded fuel-cladding interface
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
HR3 End View
HR3-A End View HR3-B End View
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
Mom
ent A
mpl
itude
(N
m)
Number of Cycles or Cycles to Failure
HBR Failure
HBR No failure
HR
Power (HBR Failure)
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
Stra
in A
mpl
itude
(%
)
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
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
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 :