PWI Modelling Meeting – EFDA C. J. Ortiz Culham, Sept. 7th- 8th, 2010 1/8

Defect formation and evolution in W under irradiation

Christophe J. Ortiz

Laboratorio Nacional de Fusión – CIEMAT, Madrid, Spain

Material group

PWI Modelling Meeting – EFDA C. J. Ortiz Culham, Sept. 7th- 8th, 2010 2/8

● High particle fluxes (>1024 m-2s-1) of mixed species (D, T, He, Ar/N/Ne)

● Intense heat flux to the surface (20 MW/m2 steady-state, ~1 GW/m2 in millisecond transients, ~10 GW/m2 if plasma control is lost)

● High neutron irradiation (~1018 m-2s-1) of 14.3 MeV neutrons

1.5 x 108 KD + T He + n

Divertor

CFC

W

Be

Issues

Microstructure evolution on W behaviour ?

Damage created by neutrons in W ?

Effect of neutron damage on H/He

retention ?

PWI Modelling Meeting – EFDA C. J. Ortiz Culham, Sept. 7th- 8th, 2010 3/8

Simulation of defect evolution in materials under irradiation

Irradiation proces takes place in nm3 and ps (neutron or ion).

Neutron irradiation produces different types of defects: I, V, He, H, clusters…

After they are created, defects can:-Migrate,-Agglomerate,-Recombine,-Dissociate,-etc…

for ns-years over large distances, which can strongly affect macroscopic properties of materials.

It is essential to predict/simulate:- Defects created by neutron/ion irradiation- Long-term evolution of defects and impurities

316 stainless steel rods before (left) and after (right) irradiation at 533°C to a fluence of 1.5×1023 neutrons m-2

PWI Modelling Meeting – EFDA C. J. Ortiz Culham, Sept. 7th- 8th, 2010 4/8

Participation in different projects:- EFDA (MAT-REMEV, W-W alloys)

Evolution of H and He in Fe/W.- IFMIF

Neutron spectra, neutron damage.

- TECHNOFUSION

Developpement of physical models and implementation of computational codes for the creation, transport and evolution of defects in materials under irradiation. Multi-scale approach.- Migration and binding energies: ab initio- Evolution of system: OKMC or Diff. Eqs.

Materials of interest for Fusion:- Structurals (Fe, FeC, FeCr, …)- Functionals (SiO2, Al2O3, SiC, …)- Divertor materials (W)

Validation of models vs experiments.

ns-years

(30-100nm)3

Mesoscopic

KineticMonte Carlo Diffusion

Ecuations

ns(10-30nm)3

Molecular Dynamics

Atomistic

1nm3

0 - ps

Ab initio

ITER-DEMO

yearsm3

Micro-macro

µm3

Dislocations

cm3

FiniteElements

(nm-m)3ns-s

Modelling approach

PWI Modelling Meeting – EFDA C. J. Ortiz Culham, Sept. 7th- 8th, 2010 5/8

Possible contribution to PWI modelling He/H irradiation in W: Penetration profile and damage

● Simulations predict almost no damage in these conditions. Clear influence of material structure on implantation profile.● Implantation results can be used as input of kinetic models (OKMC or Diff. Eqs.) to simulate transport/retention of H in W.

● The H/He profiles as well as the corresponding damage (I, V) can be calculated with MARLOWE code, based on the binary collision approximation.

- MARLOWE code allows to define the lattice structure and accounts for effects such as channeling, replacements, stenons…

- Simulations can be performed in crystal, polycrystal or amorphous materials.H 1 keV in PolyW * H 1 keV in Amorphous W *

*M. Hou, C.J. Ortiz et al, J. Nucl. Mater. 403, 89 (2010)

0 200 400 600 800 1000102

103

104

105

106

H V I

Ato

ms

/ cm

Depth (Å)

0 200 400 600 800 1000102

103

104

105

106

H V I

Ato

ms

/ cm

Depth (Å)

PWI Modelling Meeting – EFDA C. J. Ortiz Culham, Sept. 7th- 8th, 2010 6/8

Possible contribution to PWI modelling

Creation of defects in W by energetic neutrons● Energetic neutrons (~14 MeV) generates a large amount of displacement atoms (PKA) in the material with a wide energy spectrum.- The PKA spectrum can be calculated with Nuclear Data processing NJOY code.- The Energy distribution of Fluence Rate of neutrons can be calculated with MCNPX code.

● Then, the damage (I, V) corresponding to the PKA spectrum can be calculated with MARLOWE code.- MARLOWE code was recently modified at CIEMAT to account for the energy loss of ions in materials at energies higher than 25 keV/amu (MeV-GeV). It is expected W atoms could be displaced from their lattice sites with energies in the order of MeV.

0 200 400 600 800 1000 1200 1400107

108

109

V I

Ato

ms

/ cm

Depth (Å)

Damage created by 1 MeV W in WExample of PKA spectra

● Simulations predict a large amount of defects in W due to neutron irradiation. This damage, in particular vacancies, should strongly affect H/He retention.

PWI Modelling Meeting – EFDA C. J. Ortiz Culham, Sept. 7th- 8th, 2010 7/8

Possible contribution to PWI modelling

Diffusion and agglomeration of He/H in W: Retention

● Models currently implemented: Diffusion and agglomeration of He/H in W* or Fe**- Formation of mobile He: Kick-Out: Hes + I Hei

Frank-Turnbull: Hes Hei + V

- Swelling phenomenon: HenVp + Hei Hen+1Vp

HenVp + V HenVp+1

- Agglomeration/Recombination of point defects: I + V 0 In + I In+1, In + I2 In+2

Vn + V Vn+1

In + V In-1

Vn + I Vn-1● These models can be either simulated with a OKMC approach or within the framework of Rate Theory (Diffusion Eqs.). Both methods present advantages and disadvantages. They are complementary.

0.6

0.7

0.8

0.9

1

1 10 100

Temperature (K)

No

rma

lize

d n

um

be

r o

f He

Experimental data

Marlowe polycrystal

Random He

0.6

0.7

0.8

0.9

1

1 10 100

Temperature (K)

No

rma

lize

d n

um

be

r o

f He

Experimental data

Marlowe polycrystal

Random He

* Activity 5 of W-W alloys Task Force, Principal Investigator: C. S. Becquart from Lille University** C. J. Ortiz et al, Phys. Rev. B 80, 134109 (2009)

PWI Modelling Meeting – EFDA C. J. Ortiz Culham, Sept. 7th- 8th, 2010 8/8

Conclusions / Possible contributions

• He/H irradiation in W: Penetration profile and damageusing Monte Carlo simulations (MARLOWE code).The results are used as initial conditions in kinetic models.

• Diffusion and agglomeration of I/V and He/H in W: Retentionusing OKMC and Diffusion Equations (Rate Theory) approaches.Evolution of implanted H/He impurities and of defects created by W displacement (neutron irradiation).

• Displacement of W atoms by energetic neutronsusing neutronic transport codes (MCNP code), Nuclear Data Processing codes (NJOY code) and Monte Carlo simulations (MARLOWE code).These defects should strongly affect H/He evolution (retention). To be used as well as initial conditions in kinetic models.

Different processes could affect W behaviour:

Interaction with MAT-REMEV and W-W alloys Task Forces