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Long term research in low activation materials is being pursued in
fusion programs and the assessment of allowable elements and/or
impurities from safety and repository reasons are being studied at
Instituto Fusión Nuclear (DENIM), using ACAB code, for national
ignition facility (NIF) and inertial fusion energy (IFE) reactors.
Uncertainties in nuclear data are being considered, and experiments for
validation of modeling will be presented. Multiscale simulation of
radiation damage is now starting to be compared with experiments, and
results on the simplest material can be reported as a function of
impurities, temperature, and dose. Molecular dynamics (MD) allows us to
identify stress-strain curve of FeCr ferritic steels under irradiation,
and macroscopic conclusions can be advanced using simple models. However,
a neutron source of enough intensity and adequate energy spectrum is
needed which will be very peculiar in the case of pulsed IFE, as we
claimed in past years. Development of international fusion materials
irradiation facility (IFMIF) will be commented and compared with solutions
such as spallation, and others using ultra-intense lasers for obtaining
required irradiation magnitudes. Research on radiation damage in SiC
composite is being pursued at macroscopic level, but basic knowledge is
scarce. A systematic identification of type of stable defects is being
presented with a new tight binding MD technique. Our research on
simulation of silica irradiation damage will also be presented. The role
of tritium, when elemental tritium (HT) and titrated water (HTO) derive in
organically bound tritium (OBT) will be explained. The deposition and
absorption processes are now being considered in our calculations giving
more precision and accuracy to our conclusions of dosimetry effects. The
role of HT versus HTO and the importance of re-emission process will be
remarked, together with the long-term role of OBT.
Silica is one of the candidate materials for final focusing mirrors in inertial fusion reactors. This material will be exposed to high neutron irradiation fluxes during operation. Radiation damage results in point defects that can lead to obscuration of this material; that is, degradation of the optical properties of silica. In this paper we present molecular dynamic simulations of defect production in silica glass. Results on the threshold displacement energies due to oxygen Primary Knock-on Atoms (PKA) are reported concluding that a range of energies (20–40 eV) exists in which the defects have a probability to be created. In addition, we determine a range of distances for a PKA to become a stable defect out of its original position. Our present analysis is focused on the formation of Oxygen Deficient Centers (ODC).
A review of structural materials choices under irradiation
in fusion environments is presented. Results on the neutron
source term and the intensities in the structural materials
as a function of pulse time, energy, and protection is given.
The role of multiscale modeling for understanding the basic
physics in irradiated materials is explained, and simulations
of metals under pulse irradiation and SiC are reported.
The pulsed nature of the irradiation and the high neutron dose are the critical factors in an Inertial Fusion Energy reactor (IFE). The damage that structural materials suffer under these extremes conditions require a careful study and assessment. The goal of our work is to simulate, trough the multiscale modelling approach, the damage accumulation in μ-Fe under conditions relevant to a IFE Reactor. We discuss how the pulse frequency, 1 Hz, 10 Hz, and the dose rate of 10 ⊏2 and 10 ⊏1 dpa/s affect the damage production and accumulation. Results of the damage that this demanding environment can produce on a protected first structural exposed to 150 keV average recoil ion will be presented. A further comparison it has been made with the damage produced by a continuous irradiation at similar average dose.
It has long been noticed that the effect of Cu solute atoms is important for the microstructural evolution of ferritic pressure vessel steels under neutron irradiation conditions. Despite the low concentration of Cu in steel, Cu precipitates form inside the α-Fe surrounding matrix and by impeding free dislocation motion considerably contribute to the hardening of the material. It has been suggested that Cu-rich clusters and combined Cu solute atoms-defect clusters that may act as initiating structures of further precipitates nucleate during annealing of displacement cascades. In order to assess the importance of the different mechanisms taking place during collision events in the formation and later evolution of these structures, a detailed Molecular Dynamics (MD) analysis of displacement cascades in a Fe-1.3% at. Cu binary alloy has been carried out. Cascade energies ranging from 1 to 20 keV have been simulated at temperatures of 100 and 600 K using the MDCASK code, in which the Ackland-Finnis-Sinclair many-body interatomic potential has been implemented. The behaviour of metastable Cu selfinterstitial atoms (SIAs) in the form of mixed Fe-Cu features is studied as well as their impact on the resulting defect structures. It is observed that above 300 K generated Cu SIAs undergo recombination with no substantial effect on the after-cascade microstructure while at 100 K Cu SIAs remain sessile and exhibit a considerable binding to interstitial and vacancy clusters. Finally, the effect that the production of vacancies via collision cascades may have on the self diffusion of Cu solute atoms is quantitatively addressed by means of determining diffusion coefficients for Cu atoms under different microstructural conditions.
New improvements in the atomic physics models for numerically treating high density plasmas, typical of ICF, together with new algorithms for multigroup radiation transport are presented.
The performance of Large High Aspect Ratio Targets has been numerically determined by using those models implemented in a one-dimensional hydro code. Some differences from experiments are identified, and a comparative analysis with other numerical codes is given.
In this article the current capabilities at DENIM for the analysis of directly driven targets are presented. These include theoretical, computational and applied physical studies and developments of detailed simulation models for the most relevant processes in ICF. The simulation of directly driven ICF targets is carried out with the one-dimensional NORCLA code developed at DENIM. This code contains two main segments: NORMA and CLARA, able to work fully coupled and in an iterative manner. NORMA solves the hydrodynamic equations in a lagrangian mesh. It has modular programs coupled to it to treat the laser or particle beam interaction with matter. Equations of state, opacities and conductivities are taken from a DENIM atomic data library, generated externally with other codes that will also be explained in this work. CLARA solves the transport equation for neutrons, (Boltzmann), as well as for charged particles, and suprathermal electrons (Fokker-Planck), using discrete ordinates and finite element methods in the computational procedure. Parametric calculations of multilayered single-shell targets driven by heavy ion beams are also analyzed. Finally, conclusions are focused on the ongoing developments in the areas of interest such as: radiation transport, atomic physics, particle in cell method, charged particle transport, two-dimensional calculations and instabilities.
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