PWI Modelling Meeting – EFDA C. J. OrtizCulham, Sept. 7 th - 8 th, /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. OrtizCulham, Sept. 7 th - 8 th, /8 High particle fluxes (>10 24 m -2 s -1 ) of mixed species (D, T, He, Ar/N/Ne) Intense heat flux to the surface (20 MW/m 2 steady-state, ~1 GW/m 2 in millisecond transients, ~10 GW/m 2 if plasma control is lost) High neutron irradiation (~10 18 m -2 s -1 ) of 14.3 MeV neutrons 1.5 x 10 8 K D + 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. OrtizCulham, Sept. 7 th - 8 th, /8 Simulation of defect evolution in materials under irradiation Irradiation proces takes place in nm 3 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 1.5×10 23 neutrons m -2

PWI Modelling Meeting – EFDA C. J. OrtizCulham, Sept. 7 th - 8 th, /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 (SiO 2, Al 2 O 3, SiC, …) - Divertor materials (W) Validation of models vs experiments. ns-years (30-100nm) 3 Mesoscopic Kinetic Monte Carlo Diffusion Ecuations ns (10-30nm) 3 Molecular Dynamics Atomistic 1nm ps Ab initio ITER-DEMO years m3m3 Micro-macro µm 3 Dislocations cm 3 Finite Elements (nm-m) 3 ns-s Modelling approach

PWI Modelling Meeting – EFDA C. J. OrtizCulham, Sept. 7 th - 8 th, /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)

PWI Modelling Meeting – EFDA C. J. OrtizCulham, Sept. 7 th - 8 th, /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. Damage created by 1 MeV W in W Example 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. OrtizCulham, Sept. 7 th - 8 th, /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: He s + I He i Frank-Turnbull: He s He i + V - Swelling phenomenon: He n V p + He i He n+1 V p He n V p + V He n V p+1 - Agglomeration/Recombination of point defects: I + V 0 I n + I I n+1, I n + I 2 I n+2 V n + V V n+1 I n + V I n-1 V n + I V n-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. * 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, (2009)

PWI Modelling Meeting – EFDA C. J. OrtizCulham, Sept. 7 th - 8 th, /8 Conclusions / Possible contributions He/H irradiation in W: Penetration profile and damage using 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: Retention using 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 neutrons using 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