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Analytical methods for the studies of nuclear materials

Andrzej Turos Institute of Electronic Materials Technology, Warsaw, Poland and National Centre for Nuclear Studies, Otwock, Poland

VINCO Technical Meeting, November 17, 2017

http://www.ncbj.gov.pl/en

• The safe and economical operation of any nuclear power system relies to a great extent, on the success of the fuel and the materials of construction.

• During the lifetime of a nuclear power system which currently can be as long as 60 years, the materials are subject to high temperature, a corrosive environment, and damage from high-energy particles released during fission.

Nuclear materials


Nuclear Reactor 1600 MW+

3

Any solid substance inside the reactor dome is a

"nuclear material”

• The reactor vessel and many internal parts are steel, often highly alloyed with chromium and nickel.

• Some internal parts will be nickel-based superalloys,

• The fuel is often uranium oxide, sometimes doped with other elements like niobium or mixed with plutonium.

• The cladding and channels around the fuel will often be "zircaloy," lightly-alloyed zirconium base materials.

Nuclear materials


Research activities on nuclear meterials are focussed on understanding the performance

of these materials

when subjected to extreme environments.

Nuclear materials


• First, operating temperatures of the in-core materials might run above 300°C.

• Second, water itself can be a very corrosive environment.

• Third, irradiation has profound effects on materials properties and behavior over long times.

These three effects can often combine in ways that are difficult to foresee.

Enviroment in GIII reactors


• Operating temperatures of the in-core materials might run above 800°C up to 1000°C

• Cooling gas or liquid metal corrosion effects are hardly known.

• Radiation spectrum can be different from that in GIII reactors.

These three effects can often combine in ways that are difficult to foresee.

Enviroment in GIV reactors


Research scope

Establishing a relationship between atomic-scale structure and its function is an important topic in the

field of materials science.

Research scope


• Testing of real reactor materials – hot cells

• Modelling of physical processes

9

Fission


10

109 MeV

68 MeV

Fission


109 MeV Br in UO2 68 MeV Kr in UO2


• About 0.4% of fissions are ternary fissions, producing a third light nucleus such as

helium (90%) or tritium (7%).

• The fission products themselves are usually unstable and therefore radioactive

• This releases additional energy in the form of beta particles, antineutrinos, and gamma rays.

Fission


13 VINCO Technical Meeting, November 17, 2017

Fission

Prompt fission neutron energy spectrum Prompt fission neutron energy spectrum


Neutron energy spectra in reactor



Elastic scattering

M

m

Eo

Fe - M=55, n - m= 1 γ= 0,07 Threshold energy = 30 eV/0.07=428 eV

T(1MeV) = 1000 keV x 0.07 = 70 keV

Displaced host atoms – recoils

with energy ranging from 5 keV to 200 keV

are produced

Two-body collision


DISTRIBUTION OF ENERGY LOSS ALONG AN ION TRACK

18

Energy loss along the ion track


Collision cascade


PKA 10 keV

0.62 ps 8 ps

3 ps

5 ps

11.5 ps

23 ps

Averback R. S. JNM 216 (1994) 49

Molecular Dynamics simulations


21

Effects of ion bombardment


a

a relv

reli VVc

Strain effects

Usually

cVi > 0 and cVv < 0


23

Dislocations


Nuclear reaction 58Ni(n,γ)59Ni

and subsequent 59Ni(n,α)56Fe reaction

are the main source of the He production in stainless steel, which leads to the damage of structural material.


4He production

Helium gas is produced by thermal neutron capture by nickel nuclei, and to a lesser extent by boron (both elements are present in the reactor vessel material)

Radiation effects in nuclear materials

Five phenomena occur in materials by neutron irradiation in a reactor environment: • irradiation hardening, • irradiation embrittlement, • irradiation creep – (creep is the time-dependent deformation

of a metal under constant load and at high temperature (T/Tm > 0.3). The metal responds by elongating. )

• irradiation growth – (dislocations present in the lattice preferentially absorb the defects, causing them to climb)

• void swelling – ( due to vacancy accumulaton)


Material synthesis

Irradiation

Testing

Structural properties

Functional properties


Modelling Roadmap

Polycrystals


http://neon.mems.cmu.edu/rohrer/research/research.html

28

The aim is to elucidate the damage buildup and defect

transformations in single crystals subjected to ion

bombardment.

It makes it possible to accumulate large dpa in a short time.

Molecular Dynamics simulations provide

close insight on these processes in the nanoscale.

Hence, the experimental validation of such computer

simulations is the key issue in defect studies.

Validating MD with direct imaging of radiation damage.


Materials structural analysis

Ion Beam Materials Laboratory (IBML)

Fundamental irradiation

studies performed at the

IBML

• Irradiations performed on

interfaces characterized to

the atomic scale

• Post irradiation analysis

will investigate the role of

interfaces on defect

formation and accumulation

• Aids in model development

and provides initial alloy

irradiation results.

Ion Beam Materials Laboratory (Los Alamos, NM)


RBS, RBS/C, NRA, ERDA, PIXE, PIXE/C, IL (on tandem and ion implanter) SEM/FIB/EDS/EBSD/CL, SEM TEM, HRTEM, EDS, EELS XRD, HRXRD Raman spectroscopy, ……



31

Damage accumulation - single-step process

Fluence (1013

cm-2

)

0 2 4 6 8 10

Accu

mu

late

d d

am

ag

e

0.0

0.2

0.4

0.6

0.8

1.0 (a)

Fluence (1013

cm-2

)

0 5 10 150.0

0.1

0.2

0.3

0.4

(b)

Fluence (1013

cm-2

)

0 2 4 6 8 10

Accum

ula

ted d

am

age

0.0

0.2

0.4

0.6

0.8

1.0 (a)

Fluence (1013

cm-2

)

0 5 10 150.0

0.1

0.2

0.3

0.4

(b)


32 32

32

Damage accumulation in compound crystals

2 THETA [deg]

30.8 31.0 31.2 31.4 31.6

Inte

nsity

0.0

5.0e+6

1.0e+7

1.5e+7

2.0e+7

2.5e+7

3.0e+7

3.5e+7

1E14

5E14

1.2E15

fluence (x 1014

/cm2)

0.01 0.1 1 10 100 1000

dis

pla

ced

ato

ms (

at.

%)

0

20

40

60

80

100GaN

three-step accumulation model

stage I


33

Dislocations visualized by HRTEM


34

Dislocation tangle visualized by HRTEM magnification 620kx

stage II


35

RBS/C

MC simulations Damage accumulation

description

Molecular Dynamics

XRD

IL, NI,

SPIS,…

TEM

NRA/C

Raman



• Damage accumulation in nuclear materials can be studied using model single crystals subjected to ion bombardment.

• Damage buildup in compound crystals should be studied by the complementary use of appropriate techniques, typically HRTEM, HRXRD, and RBS/c.

• Molecular Dynamics simulations provides close look into collision processes on the atomic scale.

However, the validation of simulation results is indispensable.

Summary


Maybe someday we can enjoy such a view in our country

37

39

Rutherford Backscattering Spectrometry RBS/c


When the channeling ion

beam encounters a

defected region:

– probability of

scattering rises

– RBS data reveals

a damage peak

random (disoriented)

virgin (aligned)

irradiated (aligned)

RBS/c - Ion Channeling


Documents

Analytical methods for the studies of nuclear materialsproject-vinco.eu/wp-content/uploads/2017/11/08-Turos-VINCO_f.pdfRadiation effects in nuclear materials Five phenomena occur in