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Tritium Effects on Materials Overview
Presented by Michael J. MorganMaterials Science and Technology
VLT Research Highlight July 18, 2006
WSRC-MS-2006-00318
SRNL Programs on Tritium Effects
OutlinePresent an overview of tritium effects on materials programs at SRNL
I. Aging Effects on Tritium-Exposed MaterialsII. Lifecycle Engineering for Tritium Containment
VesselsIII. Welding / Repair Technologies for Tritium-
Exposed and Irradiated Steels
Emphasis on containment alloysHighlight facilities available
I. Aging Effects on Tritium-Exposed Materials
Decay helium embrittlementSusceptibility to slow crack growthHelium-induced hot cracking during welding
Containment Alloys
Radiation hardeningSeal ability degradationGas production and release
Polymers for valves
Storage capacity reducedUnrecoverable tritium Change in adsorption / desorption kineticsHelium release
Metal Hydridesfor Tritium Storage
Aging PhenomenaMaterial Class
Aging Effects on Metal Hydrides
ObjectivesIncrease understanding of tritium and decay helium effects on metal hydrides.
Develop and characterize new metal tritides of interest to the NNSA including LaNi5Al and Palladium
TasksTritium Aging Studies of Metal Hydrides for NNSA Applications
Development of Predictive Models of Tritium & 3He in Metals and Hydrides
Tritium Aging Studies of Storage and Separation Materials
Metal Hydride Investigations• Pd • Pd (thick film) on supports
(kieselguhr, alumina)• La-Ni(5-x)-Al(x) alloys –
various comps. 0>x>1.0 • La-Ni-Sn alloy• Pd alloys – Pd-Cr, Pd-Co,
Pd-Ni, Pd-Rh, Pd-Rh-Co, Pd-Al (int. ox.)
• Titanium• NdCo3• Zr-Fe-Cr alloy
Tritium Aging Phenomena in LaNi5Al
Tritium Desorption Isotherms • (80°C) for LaNi4.25Al0.75
• Various Aging Times.• Virgin Material;
■ Aged 5 Months in Tritium;
◇ Aged 5.5 Years in T2;, Aged 11.5 Years in T2.
Thermal Desorption from Aged Ti Tritides
0 100 200 300 400 500 600
T (C)
dP/d
t (a
rb u
nits
)
Ti- 6 year age - init. He/Ti = .28, age - no free HeTi-10 year age - init. He/Ti = .26, age – released He
HydrogenHelium
Aging Effects on Polymers
Objectives
• Characterize radiation damage and gas generation from polymers used in tritium processing
• EPDM, Teflon, Vespel® and UHMW-PE
• Synthesize tritium compatible polymers
• Develop radiation damage models“Effects of Tritium on UHMW-PE, PTFE, and Vespel® Polyimide”, Elliot ClarkSubmitted for presentation and publication at the 17th Topical Meeting of Fusion Energy
Degraded Valve Stem Tip
Dynamic Mechanical Analysis
A A A A A
A
AA
A AA
B B B B B
B
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B BB
B
C C C C CC
C
CC
C C
D D D D D D
D
D
D DD
A A A A A
A
AA
A A A
B B B B B
B
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B BB B
C C C C CC
C
CC
CC
D D D D D D
D
D
D DD
A A A AA
A
AA
AA A
A
B B B B B
B
B
B B
B B
C C C C CC
C
CC
CC
D D D D DD
D
D
DD
D
A A A A A
A
A
A
A
A
A
A
A
A
B B B B B
B
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C C C C CC
C
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C
C
D D D D D D
D
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D
D
D
0.0
0.1
0.2
0.3
Tan
Del
ta
-100 -50 0 50 100 150
Temperature (°C)
A 1 HzB 3 C 10 D 30
A 1 HzB 3 C 10 D 30
A 1 HzB 3 C 10 D 30
A 1 HzB 3 C 10 D 30
––––––– 1 Day air– – – – 2 Days air––––– · 6 Days air––––––– Unexposed
UHMW-PE108 Days in 1 atm T2, evacuated 15 days, time in air before test as indicate
Also unexposed1 deg C/min ramp
Universal V3.4C TA I
Viscoelastic Property Degradation From Tritium Exposure
Aging Effects on Tritium-Exposed Containment Alloys
ObjectivesIncrease understanding of tritium & decay helium effects on structural alloys. Define conditions that lead to tritium-induced crack growth in fielded components
TasksMeasure mechanical & fracture toughness properties and crack growth rates of alloys as a function of hydrogen isotope and helium contentInvestigate role of microstructures including weldments and heat-affected zones on tritium compatibilityDevelop techniques for acquiring relevant data from retired components.
• Tritium-exposure causes defect structure of nanometer-sized helium bubbles
• Bubbles associated with “punched-out” dislocation loops and clustered along dislocation lines
• Strong obstacles to dislocation motion.• Response to tritium can’t be simulated
with hydrogen and depends on material microstructure
Helium Hardened Microstructure
Tritium-exposed Microstructure
0
400
800
1200
1600
2000
0 20 40 60 80
Time, h
Load
, N
21-6-9 Stainless Steel600 appm He
Step Loaded
Held at FixedDisplacement
Unloaded
Cracking Thresholds and Crack Growth Rates
1E-10
1E-09
1E-08
1E-07
1E-06
1E-05
0 10 20 30 40 50 60 70 80 90
Stress Intensity MPa-m1/2
Cra
ck G
row
th R
ate,
m/s
300 appm Helium600 appm helium
Decay Helium Reduces
Threshold For Cracking
Tritium Causes Slow Crack Growth
Threshold Cracking Test
Fracture Surface Threshold Cracking Results
304L Stainless Steel Typical Weld Microstructure
308L Filler WireTypical Weld Ferrite Content 8-10% by Volume
40 µm 20 µm
0
2000
4000
6000
8000
0 10 20 30 40
Ferrite Content (%)
J-In
tegr
al F
ract
ure
Toug
hnes
s, lb
s / i
n. Weldments Control
Tritium Charged(50-100 appm He)100-200 appm HE
J-Integral Fracture Toughness Properties of Weldments
0
2000
4000
6000
8000
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Crack Length Increase, in.
J, lb
s / i
n.
308L-H2
304L
304L-H2
308L
• Weld ferrite prevents shrinkage cracking during weld solidification.
• Ferrite beneficial for unexposed material toughness;
• More susceptible to hydrogen / tritium embrittlement
• Aging behavior reduced in weldments in part because of greater off-gassing losses
• “The Effect of Tritium on the J-Integral Fracture Toughness Properties of Type 304L Stainless Steel Weldments” by Michael Morgan Submitted for 17th TOFE, November 2006
Defect Structure in Tritium-Aged Weldment
• Low diffraction contrast image showing helium bubbles (arrows)
• Ferrite phase free of helium bubbles
• Helium bubble from tritium decay seen in austenite only
• Results show that embrittlement from aging is lower in weldmentsthan base metals
Precision Electric Discharge Machining for Harvesting Data from Exposed Components
Wall 0.05 vs Wall 0.09
Wall Thickness (in.)
0.395 0.400 0.405 0.410 0.415 0.420 0.425 0.430 0.435 0.440 0.445
[T2]
, [3 H
e] (c
c/cc
)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.96 0.98 1.00 1.02 1.04
T2 + 3H
e (appm)
0
50
100
150
200
250
300
Dist05(in.) vs T050 Dis(in.) vs He050 Dist(in.) vs T090 Dist(in.) vs He090 Dist05(in.) vs T+He05 Dist(in.) vs T+He09 Dis(in.) vs Difference
[Sum (0.05) - Sum (0.09)]
20% Wall Penetration
(Wall 0.050)
(Wall 0.090)
Longitudinal and transverse tensile specimens cut from outer wall of reservoir mock-up
(1/2” sch 10 pipe, 0.083 inch wall)
316L Tensile Test After Tritium Service
0
20000
40000
60000
80000
100000
120000
0 0.05 0.1 0.15 0.2 0.25 0.3
Strain (in. / in)
Stre
ss (p
si)
0
2
4
6
8
10
12
Triti
um
Con
cent
ratio
n in
Air
(uC
i / c
m)
StressTritium-in-Air
II. Lifecycle Engineering for Tritium Containment Vessels
• Develop continuum models for crack propagation• Develop microstructural models for bulk regions, weld
regions and heat-affected zones• Include region’s unique properties: fracture, tritium
solubility & diffusivity, & aging• Use FEM analysis for performance prediction
Microstructural Model DevelopmentHelium Bubble-Tritium-Stress Interactions
An interesting question to be addressed is whether the grain boundary can decohere by the presence of a helium bubble and its associated tritium atmosphere
11Σ
22Σ33Σ
Grain boundary
Micromechanical approach here requires description of the grain boundary cohesiveproperties via a modified Rice-Hirththermodynamics of decohesion toaccount for non-equilibrium aspectsof decohesion along the grain boundary
Such a thermodynamic theory of decohesion has been developed by Liangand Sofronis (J. Mech. Phys. Solids, 51, 1509-1531, 2003) in the case of Nickel-base alloysTritium
Helium
Diffusion Models: Fracture Mechanics C-Specimen
0
2000
4000
6000
8000
10000
12000
0.00 0.05 0.10 0.15 0.2
Distance from the crack tip (mm)
Con
cent
ratio
n (a
ppm
)
initial condition
152 hrs, IHE - 1, 5000 psi
777 hrs, IHE - 1, 5000 psi
2000 hrs, IHE - 1, 5000 psi
Time increases
Fig.4 Finite element meshes for C-specimen
8 noded higher order elementsTotal number of elements: 1964Total number of nodes: 5986
Crack Tip Enhancement in Stainless Steel Charged and Tested in Hydrogen Gas(5000 psi)
Crack Tip Depletion From Off-Gassing Losses
0
2000
4000
6000
8000
10000
12000
0.00 0.05 0.10 0.15 0.20
Distance from the crack tip (mm)
Con
cent
ratio
n (a
ppm
)
initial condition 152 hrs, IHE - 3, 0 psi 777 hrs, IHE - 3, 0 psi2000 hrs, IHE - 3, 0 psi
No Crack Tip Enhancement in Stainless Steel Charged in Hydrogen (5000 psi) and Tested in Air
Objectives • Study the effects of helium embrittlement cracking on
Types 316LN and 304 SS plates using low heat input overlay welds and GTA stringer beads
• Characterize the He bubble microstructures in weld heat-affected zones (HAZ).
Findings• Low-heat, Low-penetration welds reduce HAZ cracking• Cracking in HAZ much more severe in 304 for both weld
types.• Much more porosity in 304 stringer beads; greater depth
of penetration in 316 welds.• He bubbles on grain boundaries in both steels, more
Cr-rich carbides in 304
•
III. Welding / Repair Technologies for Fusion Materials
Welding System
Stringer beads and overlay Welds on T2-Exposed Plate
Significantly more HAZ Cracking in 304 – 35.5 J/mm2 (22.9 kJ/in2)
Overlay Welds On Plates With 90 appm Helium
304
316LN
More Cracking & Porosity (304), Greater Depth of Penetration (316LN)
304
316LN
44.6 J/mm2
(28.8 kJ/in2)
Stringer Beads 90 appm Helium
Grain Boundary in HAZ of Overlay Weld 316LN
Helium Bubble on HAZ Grain Boundary
Summary
Tritium causes unique effects on the properties of a variety materials needed for processing tritiumIn hydride materials, tritium aging changes the thermodynamic behavior including a loss of storage capacity, unrecoverable tritium and contamination by helium releaseIn polymers, beta-radiation from tritium decay causes hardening, embrittlement, seal degradation, and gas productionIn structural alloys, tritium aging results in embrittlement andslow crack growth; severity depends on original microstructureWeld repair technologies developed for minimizing hot cracking resulting from helium from irradiation or tritium decayModeling now being utilized for improving predictive capabilities
Summary
Tritium Facilities and Capabilities:Sample charging up to 5000 psi and 350 CMechanical and fracture mechanics testing Isotherm measurements for hydridesPolymer dynamic mechanical analysisScanning and transmission electron microscopyHydrogen permeationElectric-Discharge machining and welding laboratoryModeling of tritium partitioning and effects in microstructuresModeling of structural / fracture performance of tritium-exposed materials
Tritium Effects Principal Investigators
Structural alloys: Dr. Michael J. MorganPolymers: Dr. Elliot ClarkMetal Hydrides: Dr. D. Thomas WaltersMicroscopy / Welding Technologies: Dr. Michael Tosten
Contact Dr. Robert Sindelar for additional information