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Perspective on Radial-Hydride-Induced Embrittlement
Mike Billone Argonne National Laboratory
DOE-UFD Annual Meeting
UNLV June 7-9, 2016
2
Introduction Background Relevant ranges of peak cladding temperature and stress
Previous Results for High-Exposure Cladding ─ As-irradiated cladding ─ Following cooling from 400oC peak drying-storage temp.
New Data for High-Exposure Cladding ─ As-irradiated condition for Zry-4 ─ Following cooling from 350oC peak drying-storage temp.
FY2016 Tests in Progress
Summary and Perspectives
Outline of Topics
3
Introduction
4
Introduction: Objectives of Argonne Experimental Program
Argonne Experimental Program • Generate data for ductility vs. temperature following slow cooling
from T ≤400°C and decreasing hoop stress (σθ) • Determine ductile-to-brittle transition temperature (DBTT) for each
set of peak drying-storage T and σθ: ductility transition temperature • Characterize extent of radial hydrides and correlate DBTT with
effective length of radial hydrides (RHCF) • From data and stress-strain input, determine failure stresses and
strains for PWR cladding alloys (input into codes) Argonne Collaborations
• EPRI-ESCP Fuels Subcommittee and ORNL: relevant range for σθ • PNNL and ORNL: relevant range for peak cladding temperatures • SNL, PNNL, and ORNL: relevant range of NCT loads and fueled-
cladding response to bending-fatigue loads (experimental)
5
Introduction: Loads on Fuel Rods
Loads on Fuel-Rod Cladding during Drying & Storage • Primarily internal gas-pressure loading (hoop & axial stresses)
Loads on Fuel-Rod Cladding during Transport • Normal conditions of transport (NCT) include vibration and shock
– Axial bending: axial bending stresses (other stresses at pellet-pellet interfaces) – “Pinch” loading at grid spacers: hoop bending stresses
• Hypothetical accident conditions include severe impact loads
F
Internal Pressure pi
Schematic of Pinch-Loading
6
Introduction: Circumferential and Radial Hydrides in High-Exposure PWR Cladding
320 wppm H
As-Irradiated After Cooling from 400oC/110-MPa
76 wppm H
72 wppm H
350 wppm H
ZIRLO™
M5®
7
Introduction: Relevant Ranges of Cladding Temperature & Stress
Cladding Temperature • Peak cladding temperature (PCT)
– Determines maximum hydrogen content in solution and available for precipitation as radial hydrides: 206 wppm @ 400°C, 126 wppm @ 350°C, 77 wppm @ 300°C
– Likely to occur during vacuum drying – 400°C NRC-recommended limit; ≤350°C based on UFD S&T calculations
• “Peak” average gas temperature within fuel rods – Determines peak internal pressure given pressure (RIP) at RT – May vary from 180°C (vacuum/static-He) to 340°C (vertical cask with 0.5-MPa He)
Cladding Hoop Stress • Depends on rod internal/external pressure, ID, and wall thickness • “Reasonable” upper bounds for high-burnup PWR fuel rods
– Standard (UO2/Clad) fuel rods: 60−80 MPa – Integral Fuel Burnable Absorber (IFBA fuel rods (UO2/10B/ZIRLO™):
• Hollow blanket pellets (HBP): 80−120 MPa; solid blanket pellets (SBP): 115−155 MPa
8
Introduction: Dissolution (Heating) and Precipitation (Cooling) Curves
0
50
100
150
200
250
300
350
400
450
0 100 200 300 400 500
Hyd
roge
n C
once
ntra
tion
(wpp
m)
Temperature (°C)
Kammenzind Cd (Zry-4)Kammenzind Cp (Zry-4)Kearns Cd (Zr,Zry-2,Zry-4)
Dissolution
Precipitation
ΔTPD 210 wppm
77 wppm
9
Combined Data and Predictions for Rod Internal Pressure (RIP) @ 25oC
0
1
2
3
4
5
6
7
8
9
10
11
40 45 50 55 60 65 70 75
EOL
PWR
RIP
at 2
5°C
(MPa
)
Rod Average Burnup (GWd/MTU)
Data: Standard RodsFRAPCON: Standard RodsFRAPCON-IFBA-HBPFRAPCON-IFBA-SBP
Data Average + 3-σ
Data Average
10
Summary of Previous Results: Cooling from 400oC
11
Response of M5® Cladding following Cooling from 400oC
Test Matrix for High-Exposure M5® (Zr-1wt.%Nb)
• As-irradiated, 76±5 wppm hydrogen • After cooling from 400°C/90-MPa, 58±15 wppm • After cooling from 400°C/111-MPa, 72±10 wppm • After cooling from 400°C/142-MPa, 94±4 wppm
Results for High-Exposure M5® • As-irradiated: high ductility at T ≥20°C (no cracking up through 1.7 mm disp.)
• 90-MPa, 58±15 wppm: high ductility at T ≥20°C, 37±17% RHCF
• 111-MPa, 72±10 wppm: high ductility at T ≥90°C, 54±20% RHCF
• 142-MPa, 94±6 wppm: mod.-to-high ductility at T ≥90°C, 61±18% RHCF
12
Ductility vs. Test Temperature for High-Exposure M5®
0
2
4
6
8
10
12
14
0 25 50 75 100 125 150 175 200 225
Offs
et S
trai
n (%
)
RCT Temperature (°C)
76±5 wppm H58±15 wppm H (90 MPa)72±10 wppm H (111 MPa)94±6 wppm H (142 MPa)
142 MPa at 400°C
111 MPa at 400°C
Ductile
Brittle
High-Burnup M5®
As-Irradiated
90 MPa at 400°C
13
Radial Hydrides in High-Exposure M5® following Cooling from 400oC
111 MPa 72±10 wppm
82 MPa at 228oC 54±20% RHCF
90 MPa 58±15 wppm
65 MPa at 210oC 37±17% RHCF
142 MPa
94±6 wppm 110 MPa at 251oC 61±18% RHCF
14
Assessment of M5® Database following Cooling from 400oC
Need Data for 90−110 MPa with 75−95 wppm Hydrogen
• Ductility improved with decrease in both hydrogen and hoop stress • Note: licensing issue; PCT ≤350°C, Peak σθ <80 MPa • Low H-content and low σθ → no radial hydride issue
Need End-of-Life (EOL) RIP Data for M5®-clad fuel rods • No available data • ≤9 new data points planned for “sister” rod characterization
Need Tests at <400°C • Less annealing would occur at lower peak temperatures • Need to confirm previous results at T ≤350°C
15
Response of Zry-4 Cladding following Cooling from 400oC
Test Matrix for High-Exposure Zircaloy-4 • As-Irradiated, 300±15, 616±78, 640±140 wppm hydrogen • After cooling from 400°C/113-MPa, 520±90 wppm hydrogen • After cooling from 400°C/145-MPa, 615±82 wppm hydrogen
Results for High-Exposure Zircaloy-4 • As-irradiated
– 300±15 wppm: high ductility at 20°C (no cracking to 1.7 mm displace.) – 640±140 wppm (>850 wppm local): no-to-low ductility at ≤90°C (brittle?) – 616±78 wppm: refined test method, ductility = 2.6±0.7% vs. 1% limit
• 113 MPa, 520±90 wppm: low ductility at 20°C, 9±5% RHCF – Recommended test at 350°C/110-MPa (4 RCT data points at 20°C)
• 145 MPa, 615±82 wppm: low ductility at 90°C, 16±4% RHCF
16
Ductility vs. Test Temperature for High-Exposure Zircaloy-4
0
2
4
6
8
10
12
14
0 25 50 75 100 125 150 175 200 225
Offs
et S
trai
n (%
)
RCT Temperature (°C)
300±15 wppm H640±140 wppm H520±90 wppm H615±82 wppm H
Brittle
Ductile
145 MPa at 400°C
113 MPa at 400°C
High-Burnup Zircaloy-4
As-Irradiated
17
Ductility vs. Test Temperature for As-Irradiated, High-Exposure Zry-4
0
1
2
3
4
5
6
7
8
9
10
0 20 40 60 80 100 120 140 160
Perm
anen
t Str
ain
(%)
RCT Temperature (°C)
300±15 wppm H
640±140 wppm H
616±78 wppm H
Ductile
As-Irradiated High-Burnup
Zircaloy-4
18
Crack Depth vs. Load Drop for As-Irradiated Zry-4: Load-Interrupt Tests
44% Wall Crack 27% Load Drop 2.1% “Ductility”
41% Wall Crack 22% Load Drop 2.2% “Ductility”
39% Wall Crack 24% Load Drop 2.7% “Ductility”
19
Response of ZIRLO™ Cladding following Cooling from 400oC
Test Matrix for High-Exposure ZIRLO™ (Zr-1wt.%Nb-1wt.%Sn)
• As-Irradiated, 530±70 wppm hydrogen • After cooling from 400°C/80-MPa, 535±50 wppm hydrogen • After cooling from 400°C/89-MPa, 530±115 wppm hydrogen • After 3-cycle cooling from 400°C/88-MPa, 480±131 wppm hydrogen • After cooling from 400°C/111-MPa, 385±80 wppm hydrogen (2 tests) • After cooling from 400°C/141-MPa, 650±190 wppm hydrogen
Results for High-Exposure ZIRLO™
• As-irradiated, 530±70 wppm: mod.-to-high ductility at T ≥20°C • 80 MPa, 535±50 wppm: mod-to-high ductility at T ≥20°C, 9±3% RHCF • 89 MPa, 530±115 wppm: low ductility at 23°C, 19±9% RHCF • 88 MPa, 480±131 wppm: low ductility at 23°C, 20±9% RHCF (3-cycle cool.) • 111 MPa, 350±80 wppm: high ductility at 150°C, 32±13% RHCF • 141 MPa, 650±190 wppm: brittle at 150°C, mod. ductility at 195°C
20
Ductility vs. Test Temperature for High-Exposure ZIRLO™
0
2
4
6
8
10
12
14
0 20 40 60 80 100 120 140 160 180
Offs
et S
trai
n (%
)
RCT Temperature (°C)
530±70 wppm H
535±50 wppm H
530±115 wppm H
480±131 wppm H
385±80 wppm H
Brittle
Ductile
111 MPa at 400°C
80 MPa at 400°C
High-Burnup ZIRLO™ As-Irradiated
89 MPa at 400°C
21
Radial Hydrides in High-Exposure ZIRLO™ following Cooling from 400oC
141 MPa (128 MPa @ Tp)
650 wppm
111 MPa (101 MPa @ Tp)
350 wppm
80 MPa (72 MPa @ Tp)
535 wppm
89 MPa (80 MPa @ Tp)
530 wppm
22
Response of ZIRLO™ Cladding following Cooling from 400oC
Assessment of Database for High-Exposure ZIRLO™ • Need data in peak stress range of 90−110 MPa prior to cooling
– DBTT increased by 100°C within this stress range – Stress range relevant to WEC-IFBA rods
• Need repeat tests to determine DBTT with more precision – Standard-fuel ZIRLO™ rods: 60−80 MPa relevant peak stress range
• Radial hydride embrittlement not anticipated
– ZIRLO™-clad fuel pellets with ZrB2 (enriched in 10B) coating Integral Fuel Burnable Absorber (IFBA) rods Relevant stress ranges: 80−120 MPa and 115-155 MPa for 2 designs
• Need tests at <400°C to determine net effects on DBTT of reduction in annealing and reduction in dissolved hydrogen available for precipitation
23
New Data for 350oC Peak Drying-Storage Temperature
24
High-Exposure ZIRLO™ and M5® following Cooling from 350oC
Expectations • ZIRLO™
– Decrease (80 wppm) in dissolved hydrogen and in precipitation temperature – Decrease in internal pressure and hoop stress at precipitation initiation – Possible decrease in annealing of irradiation hardening (lower ductility matrix) – Anticipated net effect: decrease in DBTT
• M5® – No change in dissolved hydrogen, precipitation temperature, precipitation stress – Possible decrease in annealing of irradiation hardening (lower ductility matrix) – Anticipated net effect: no change in DBTT
ZIRLO™ Tests at 350°C • 94 MPa (84 MPa @ Tp), 644±172 wppm, 1-cycle cooling
– Long radial hydrides (37±11%), low ductility @ ≤135°C, mod. ductility @ 150°C • 93 MPa (83 MPa @ Tp), 564±177 wppm, 3-cycle cooling
– Long radial hydrides (30±11%), low ductility @ ≤120°C, high ductility @ ≥135°C • No effects of cycling, but DBTT comparable to DBTT for 400°C/111-MPa
25
Ductility Data for High-Exposure ZIRLO™ following Cooling from 350oC
0
2
4
6
8
10
12
14
0 20 40 60 80 100 120 140 160
Offs
et S
trai
n (%
)
RCT Temperature (°C)
400°C/89-MPa, 530±115 wppm, 1C400°C/88-MPa, 480±131 wppm, 3C350°C/93-MPa, 564±177 wppm, 3C350°C/94-MPa, 644±172 wppm, 1C400°/111-MPa, 350±80 wppm, 1C400°/111-MPa, 425±63 wppm, 1C
Brittle
Ductile
High-Burnup ZIRLO™
26
Radial Hydrides in ZIRLO™ for 1- and 3-Cycle Drying Tests following cooling from 350oC
1-Cycle-350oC Test 94 MPa → 84 MPa
37±11% RHCF ≥50% Max. RHCF
3-Cycle-350oC Test 93 MPa → 83 MPa
30±11% RHCF ≥50% Max. RHCF
27
FY2016 Tests in Progress
ZIRLO™ following Cooling from 350°C • 90-MPa (1-cycle) test with lower-H (350 wppm) and 24-h hold time
– High-hydrogen content (644±172 wppm) may have degraded cladding – 350 wppm is closer to expected hydrogen content at ≤55 GWd/MTU – Compare results to 400°C/111-MPa test with 350 wppm & 24-h hold – Use load-interrupt method to improve data analysis and reduce scatter – If ductility values are still low, investigate effects of annealing
M5® following Cooling from 350°C • 90-MPa target hoop stress, 75−95 wppm target H-content
– Radial hydride treatment (RHT) completed – Metallography: oxide and metal wall thicknesses, 50±14% RHCF – 89-MPa actual hoop stress – Hydrogen content: 80±7 wppm; hydrides not continuous in axial
direction; ring compression tests in progress
28
ANL Perspective
DBTT or Ductility Transition Temperature • Not a material property like Young’s modulus • Depends on orientation/length of hydrides and orientation of loads • Transport at T <DBTT does not imply failure • ANL data may be used to determine hoop failure stresses/strains
Relevant Hoop Stresses during Drying and Storage • Depend on end-of-life internal gas pressures
– Standard rods have lower gas pressures (He-fill + fission gas) – IFBA rods have higher gas pressures (He-fill + He from B-10 + fission gas)
• Depend on average gas temperature during drying/storage – Horizontal/He < vertical/vacuum < vertical/He < vertical/convective-He
• “Reasonable” upper-bound hoop stresses – Standard PWR rods: 60−80 MPa – ZIRLO™-clad IFBA rods with annular blanket pellets: 80−120 MPa – ZIRLO™-clad IFBA rods with solid blanket pellets: 115−155 MPa
29
Relevant Publications
M.C. Billone et al. Phase I Ring Compression Testing of High-Burnup Cladding. FCRD-
USED-2012-000039, Dec. 21, 2011. M.C. Billone et al. Baseline Studies for Ring Compression Testing of High-Burnup
Fuel Cladding. FCRD-USED-2013-000040, ANL-12/58, Nov. 23, 2012. M.C. Billone et al. “Ductile-to-brittle transition temperature for high-burnup cladding
alloys exposed to simulated drying-storage conditions,” J. Nucl. Mater. 433 (2013) 431-448.
M.C. Billone et al., “Effects Drying and Storage on High-Burnup Cladding Ductility,” Proc. IHLRWM Conf., Albuquerque, NM, Apr. 28 – May 2, 2013.
M.C. Billone et al., “Baseline Properties and DBTT of High-Burnup PWR Fuel Cladding Alloys,” PATRAM-2013, San Francisco, CA, Aug. 18-23, 2013.
M.C. Billone et al. Embrittlement and DBTT of High-Burnup PWR Fuel Cladding Alloys. FCRD-UFD-2013-000401, ANL-13/16, Sept. 30, 2013.
M.C. Billone et al. Effects of Multiple Drying Cycles on High-Burnup PWR Cladding Alloys. FCRD-UFD-2014-000052, ANL-14/11, Sept. 26, 2014.
M.C. Billone et al., “Characterization and Effects of Hydrides in High-Burnup PWR Cladding Alloys,” Proc. IHLRWM Conf., Charleston, SC, Apr. 12–16, 2015.
M.C. Billone et al., Effects of Lower Drying-Storage Temperatures on the DBTT of High-Burnup PWR Cladding. FCRD-UFD-2015-000008, ANL-15/21, Aug. 28, 2015.
30
Acknowledgment
This work is supported by the Used Fuel Disposition Research and Development, Office of Nuclear Energy (NE-53) under Contract DE-AC02-06CH11357.
Mike Billone Manager, Irradiation Performance Nuclear Engineering Division Argonne National Laboratory 9700 S. Cass Ave., Bldg. 212 Argonne, IL 60439 630-252-7146 billone@anl.gov
31
Backup Slides
32
“Reasonable” Upper-Bound Hoop Stresses for Standard PWR Rods
50
60
70
80
90
100
160 180 200 220 240 260 280 300 320 340 360
PWR
Rod
Hoo
p St
ress
(MPa
)
Gas Temperature (°C)
10-Micron Oxide40-Micron Oxide80-Micron Oxide
33
“Reasonable” Upper-Bound Hoop Stresses for Standard PWR Rods
80
90
100
110
120
130
140
150
160
160 180 200 220 240 260 280 300 320 340 360
PWR
Rod
Hoo
p St
ress
(MPa
)
Gas Temperature (°C)
IFBA-HBPIFBA-SBP
34
RHT Experimental Method for 1- and 3-Cycle Drying of Pressurized Rodlet
Rodlet Fabrication 175
200
225
250
275
300
325
350
375
400
425
0 10 20 30 40 50 60 70 80 90
Tem
pera
ture
(°C
)
Time (hours)
Peak T ≤206 wppm H
in solution
Precipitation T
5°C/h
Δp = Δp(T) σθ = σθ(T) 1-Cycle
Drying
35
Temperature Histories for 1- and 3-Cycle Tests at 350oC Peak RHT Temperature
175
200
225
250
275
300
325
350
375
0 10 20 30 40 50 60 70 80
Tem
pera
ture
(°C
)
Time (Hours)
4.8°C/h
126-wppm H in solution
Precipitation Temperature
(285°C)
1 Cycle
36
Ring Compression Test (RCT)
Applied load @ 12 o’clock
Ductility: permanent (dp/Dmo) or offset strain (δp/Dmo) prior to >50% wall crack
Embrittlement: dp/Dmo <1% or δp/Dmo <2%
Controlled displacement rates 5 mm/s typical
1.7-mm maximum displacement
Controlled temperature
Maximum δp/Dmo ≈10% for 1.7 mm displacement
37
RCT Benchmark Test with As-Fabricated M5®
0.0
0.1
0.2
0.3
0.4
0.5
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Load
(P in
kN
)
Displacement (δ in mm)
KLM = 1.06 kN/mm
Offset Displacement = 0.94 mm Permanent Displacement = 0.83 mm
KLC = 1.23 kN/mm 0.94 mm
KUM = 0.81 kN/mm
0.83 mm
38
RCT Benchmark Tests with As-Fabricated and High-Exposure M5®
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Unl
oadi
ng/L
oadi
ng S
tiffn
ess
Rat
io
Offset Strain (%)
As-Fabricated Cladding
High-Burnup Cladding
39
Load-Displacement Curve and Crack at ≈6 O’Clock for 3-Cycle Rodlet Tested at 135oC RCT
0.0
0.1
0.2
0.3
0.4
0.5
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Load
(kN
)
Displacement (mm)
Ring 105E3 at 135°C 564±177 wppm H 30±11% RHCF 11.9% Offset Strain
KLM = 0.90 kN/mm
478 N 423 N
1.12 mm
KU = 0.70 kN/mm
40
Load-Displacement Curves for 1-Cycle Rodlet Tested at 135oC RCT
0.0
0.1
0.2
0.3
0.4
0.5
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Load
(kN
)
Displacement (mm)
Ring 105F3 at 135°C 644±172 wppm H 37±11% RHCF 1.1% Offset Strain
KLM = 0.90 kN/mm
449 N
43%
0.10 mm
KU = 0.88 kN/mm
41
Load-Displacement Curve and Crack at 12 O’Clock for 1-Cycle Rodlet Tested at 150oC RCT
0.0
0.1
0.2
0.3
0.4
0.5
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Load
(kN
)
Displacement (mm)
Ring 105F7 at 150°C 644±172 wppm H 37±11% RHCF 2.9% Offset Strain
KLM = 0.86 kN/mm
322 N
281 N
25%
0.27 mm
KU = 0.79 kN/mm
42
Radial Hydrides in High-Exposure M5® following Cooling from 350oC/89-MPa
Maximum – 95% RHCF
43
Radial Hydrides in High-Exposure M5® following Cooling from 350oC/89-MPa; after Grinding off 0.5 mm & Polishing
Maximum – 95% RHCF
44
Radial Hydrides in High-Exposure M5® following Cooling from 350oC/89-MPa; after Grinding off ≈0.1 mm & Polishing
Maximum – 91% RHCF
Recommended