Strategies for Mitigating Strategies for Mitigating Swelling in Austenitic Swelling in Austenitic

Stainless Steels in Fast Stainless Steels in Fast Reactors Reactors

NERS 521 – Final PresentationNERS 521 – Final Presentation

David SirajuddinDavid Sirajuddin

Nuclear Engineering & Radiological SciencesNuclear Engineering & Radiological Sciences

OutlineOutline

Definitions – voids, swelling

Swelling dependencies

Overview of Fast Reactor environment and material demands – Proposed material: Austenitic Stainless Steel

Techniques for mitigating swelling:

I. Cold-working (CW)II. Impurity atom introductionIII. Compositional changes

Summary & Conclusions

Swelling is a macroscopic effect of Swelling is a macroscopic effect of void formation and growthvoid formation and growthVoids = aggregation of vacanciesVoid formation and growth swellingSwelling can be quantified as percent volume change, DV/V [%], in a material

Low swelling rate transient region

Higher swelling rate steady state region ~ 1%/dpa

Void growth and formation dependentsVoid growth and formation dependents

Approximate void growth equation[Brailsford and Bullough]

Dose: Swelling increases with dose Dose Rates: Swelling decreases with dose rate

Temperature: Maximum peak exhibited at intermediate temperature, minimumthreshold for void growth

;

[Was]

FR environment demands materials that FR environment demands materials that can withstand harsher environmentscan withstand harsher environments

Approximate operating environments of Gen IV Fast Reactor (FR) systems

[Allen]

Austenitic stainless steels have been proposed for fuel cladding, baffles, etc. materials for FR components

Reactor Type Coolant Inlet Temperature (oC)

Coolant Outlet Temperature (oC)

Maximum Dose (dpa)

PWR 290 320 100

SCWR 290 500 15-67

VHTR 600 1000 1-10

SFR 370 550 200

LFR 600 800 200

GFR 450 850 200

MSR 700 1000 200

What this means…What this means…

Bad News: Swelling alters material properties and dimensions of austenitic stainless steels materials change from intended design parameters during operation!

More Bad News: All operating temperatures of FRs encourage void formation and growth in austenitic stainless steels (SS)

But,

Good News: Swelling can be mitigated by material treatments, and material compositional changes

ObjectiveObjective

Find treatments and changes that can be applied to austenitic stainless steels to make them more swelling resistant

[Porolla, et al][Encyclopedia Brittanica]

Swelling can be reduced by Swelling can be reduced by discouraging void growthdiscouraging void growth

General Strategy: Extend transient region of swelling vs. accumulated dose curve

Specific Strategies:

i. Cold-working (CW)ii. Addition of impuritiesiii. Fine-tune alloy compositioniv. Use a different phase of steel!

Cold-working dampens void growth by Cold-working dampens void growth by extending the transient regionextending the transient region

Increased CW decreases material swelling by extending the transient region CW dampens the swelling peak in temperature dependence

All same slope!

[Was, Dupuoy et al, Busboom et al]

Impurity introduction discourages void Impurity introduction discourages void nucleation nucleation reduction of swelling reduction of swelling

Introduction of impurity atoms decrease swelling

soluble atoms bind with point defects, reducing mobility and encouraging recombination

Examples: Si, P, Hf (oversized)

Trend shows increasing binding energy increased activation energy of voids void growth surpressed

[Mansur et al, Was]

Impurity introduction cont’dImpurity introduction cont’d

Phosphorous and Silicon implantation decrease swelling

[Garner, et al., Was] [Garner, et al., Was]

Alloy composition can be fine-tuned to Alloy composition can be fine-tuned to better accommodate swellingbetter accommodate swelling

Increased Ni concentration extends the transient region This extension decreases swelling Decreasing trend continues until a minimum is reached at 50 at% [Was].

[Ukai, et al]

[Garner et al, Was]

Conclusions & SummaryConclusions & Summary

Material composition changes and treatments dampen swelling!

Impurity atoms inhibit voidnucleation,

Ni content increase extends incubation period

CW prolongs transient region

[Allen]

ReferencesReferences

1. S. Ukai, et al. Swelling rate versus swelling correlation in 20% cold-worked 316 stainlesssteels. Journal of Nuclear Materials. 15 December 2002.

2. E. R. Gilbert, et al. The influence of Cold-work level on the irradiation creep and swelling ofAISI 316 stainless steel irradiated as pressurized tubes in the EBR-II fast reactor. Journal ofNuclear Materials.

3. N. Igata et al. Effect of light impurities on the early stage of swelling in austenitic stainlesssteel. Journal of Nuclear Materials 258263 (1998) 1735-1739.

4. Surh, Michael P. Vacancy cluster evolution and swelling in irradiated 316 stainless steel.Journal of Nuclear Materials 328 (2004) 107114. March 2005.

5. G. S. Was. Fundamentals of Radiation Materials Science. Springer-Verlag Berlin Heidelberg. New York. 2007.

6. M. P. Surh, J. B. Sturgeon, W. G. Wolfer The Incubation Period for Void Swelling and itsDependence on Temperature, Dose Rate, and Dislocation Structure Evolution. 21st Symposiumon Effects of Radiation on Materials, Tucson, AZ.

7. K.C. Russella. Void nucleation with embryo injection Departments of Materials Science andEngineering and Nuclear Science and Engineering, Massachusetts Institute of Technology,Cambridge, MA 02139, USA

8. E. P. Simonenb, S. M. Bruemmerb, L. Fournierc, B. H. Sencerc and G. S. Was The effect ofoversized solute additions on the microstructure of 316SS irradiated with 5 MeV Ni++ ionsor 3.2 MeV protons. Received 6 June 2002; accepted 11 November 2003. ; Available online20 December 2003.

Questions?Questions?

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