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

B

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

B

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

B

B

B

B

B

B

C C C C CC

C

C

C

C

C

D D D D D D

D

D

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