Kristina Lindgren Supervisors: Krystyna Stiller, Mattias Thuvander Vattenfall contact: Pål Efsing

Irradiation induced precipitation in reactor pressure vessel steel welds

Reactor Pressure Vessel Low alloy steel, cladded with stainless steel

https://en.wikipedia.org/wiki/Nuclear_power_plant#/media/File:PressurizedWaterReactor.gif

Welds are most susceptible Radiation and heat

PWR

Ringhals R4 at% Low Cu, high Ni

[Brumovsky 2010]

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Radiation induced precipitation

[Odette, 2009]

• Nanometre precipitates contain Ni, Mn, Si and Cu

• High Ni steels: more Ni, Mn and Si in the precipitates

• Late blooming phases?

• Accelerated embrittlement!?

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• What are the characteristics of the precipitates?

• How do they evolve? • Do we have “late blooming precipitates”,

i. e. an acceleration in embrittlement? • What does the accelerated irradiation tell us

about the actual, low flux, RPV?

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Materials

Name Fluence (1023 n/m2)

Flux (1016 n/(m2s))

Reference 0 - H2.0 2.0 2.31 H6.4 6.4 3.81 S4.6 4.6 0.15

Still high flux compared to actual RPV

Corresponding approx. years in reactor

0 ~20 ~60 ~45

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Hardness measurements

• Hardness - embrittlement

(data from Magnus Boåsen)

Atom probe tomography

X, Y

X, Y

Field Evaporation

Position Sensitive Detector

3D Reconstruction

+DC

ToF-MS

Atom Probe Tomography Experimental

• Detection efficiency 37% • Typical analyzed volume:

50x50x200 nm3 • Parameters:

- Voltage 20% pulse fraction, 50 K, 200 kHz - Laser 0.3 nJ, 30 K, 200 kHz

• Specimen preparation: FIB/SEM

Photo from Chalmers homepage: https://www.chalmers.se/en/researchinfrastructure/CMAL/instruments/APT/Pages/default.aspx

Results: Clusters

H6.4 ~60 years

(nm)

Orange – Cu atoms

Green isoconcentration surfaces Ni+Mn+Si=8.2%

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Cluster number density and size distribution

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Cluster composition H2.0 H6.4 S4.6

Note: different length of analysis

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Cluster composition Mn/Ni Si/Ni Cu/Ni

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Conclusions • Number density and size increase with fluence • No late blooming precipitates • Flux effects: Surveillance material have the same type of

clusters (but less Cu). • Larger clusters (-> larger contribution to embrittlement) • Lower number density (-> smaller contribution to embrittlement)

• The actual RPV...

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Future work

• APT of PIA (post irradiation annealed) material from Ringhals – Halden (collaboration with Magnus Boåsen, KTH)

• APT of samples exposed in the ICEWATER project

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Publications

• Lindgren, K., Stiller, K., Efsing, P., Thuvander, M. On the analysis of clustering in an irradiated low alloy reactor pressure vessel steel weld. Microscopy and Microanalysis, submitted

• Lindgren, K., Boåsen, M., Efsing, P., Stiller, K., Thuvander, M. Evolution of radiation induced precipitates in reactor pressure vessel steel welds (Tentative title). Writing in progress.

Licentiate seminar November 29th 10.00

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“It has long been an axiom of mine that the little things are infinitely the most important” Sherlock Holmes, A Case of Identity, Sir Arthur Conan Doyle