Aging of RPV Steel – An Atom Probe Tomography Study

Kristina Lindgren, PhD student Mattias Thuvander (supervisor)

Division of Materials Microstructure Department of Applied Physics

Chalmers University of Technology

Part of MÅBIL

The project

• What happens on a microstructural scale in the reactor pressure vessel welds after long times in the reactor?

• The RPV is a life limiting component

Long term aging on the atomic scale

Geography

VTT Mechanical testing

Halden Test reactor Irradiation of steel

Chalmers

Ringhals, R4

Reactor Pressure Vessel

Low alloy steel, cladded with stainless steel

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

Welds are the weakest part

Radiation and heat

PWR

At% Low Cu, high Ni!

Neutron Radiation Damage

• Direct matrix damage; vacancies and interstitials

• Segregation to grain boundaries, P

• Precipitation Cu and Mn Ni Si - Cu-rich precipitates,

may contain Mn, Si, Ni - Mn, Si, Ni – “late

blooming effects”?

[Brumovsky 2010]

Ringhals: low Cu high Ni

• Contribution from Ni, Mn, Si rich precipitates after long times

• Not well understood

?

[Brumovsky 2010]

How do the clusters evolve during long term operation??

Atom probe tomography

X, Y

X, Y

Field Evaporation

Position Sensitive Detector

3D Reconstruction

+DC

ToF-MS

Atom probe tomography

• Atomic resolution • Our instrument detectability of 37% • Volumes of ~ 50 x 50 x 200 nm3

• Needle shaped specimen – prepared using FIB/SEM or electropolishing

Focused Ion Beam / Scanning Electron Microscope Image (e or Ga), deposit Pt, mill away material using Ga ions Small volumes of material!

FIB/SEM sample preparation

Specimen

Clusters

~60 years

Orange – Cu atoms

Isoconcentration surfaces Ni+Mn+Si=8.2%

Distribution of elements in clusters

Cu+Ni+Mn+Si

A thin slice of the analysis ~60 years

Proxigram

20 years 30 years 60 years

Increased amount of Si in clusters

Calculated from the isoconcentration surfaces

0

2

4

6

8

10

12

14

0 2 4 6 8

Num

ber d

ensi

ty 1

0^23

clu

ster

s/m

^2

Fluence 10^19 n/cm^2

Number density of clusters

Number density for each run

Average number density

High Cu, Ni AND

No clusters, Ga implantation, boundary

Increasing trend?

#clusters/volume

Size distribution

Cluster algorithm, Ni+Mn, Nmin=18, dmax=0.5 nm

Bimodal distribution? Not only coarsening

~20 years

~30 years

~60 years

P distribution

Purple – P atoms

Isoconcentration surfaces Ni+Mn+Si=8.2% ~60 years

Ongoing work

• More data for statistics • Compare with surveillance material – effect of heat • Evaluating the data!