D. Lodi

Multiscale modeling study of pulsed damage accumulation in α-Fe under inertial fusion conditions

Abstract Reduced activation ferritic–martensitic (RAFM) steels are being considered as candidate materials for the first structural wall of a future fusion reactor, due to their high resistance to neutron irradiation. A combination of molecular dynamics and kinetic Monte Carlo has been utilized to analyze and assess the change and evolution of the microstructure in irradiated α-Fe, the main component of RAFM steels. We discuss how the pulse frequency, 1 and 10 Hz, may affect the damage production and accumulation. Dose rates of 0.1 and 0.01 dpa/s will be considered in order to represent the damage suffered by a protected first structural wall. These results will be compared with previous work on the subject and with those achieved with continuous irradiation at similar average dose rate.

Pulse frequency effect on neutron damage in α-Iron:A KMC analysis

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 modeling approach, the damage accumulation in {alpha}-Fe under conditions relevant to a IFE Reactor. We discuss how the pulse frequency, 1 Hz, 10 Hz, and the dose rate of 10{_} and 10{_}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.

DIRECT COMPARISON BETWEEN MODELING AND EXPERIMENT: AN α-Fe ION IMPLANTATION STUDY

Advances in computational capability and modeling techniques, as well as improvements in experimental characterization methods offer the possibility of directly comparing modeling and experiment investigations of irradiation effects in metals. As part of a collaboration among the Instituto de Fusion Nuclear (DENIM), Lawrence Livermore National Laboratory (LLNL) and CIEMAT, single and polycrystalline α-Fe samples have been irradiated with 150 keV Feions to doses up to several dpa. The irradiated microstructure is to be examined with both transmission electron microscopy (TEM) and positron annihilation spectroscopy (PAS). Concurrently, we have modeled the damage accumulation in Fe under these irradiation conditions using a combination of molecular dynamics (MD) and kinetic Monte Carlo (KMC). We aim to make direct comparison between the simulation results and the experiments by simulating TEM images and estimating positron lifetimes for the predicted microstructures. While the identity of the matrix defect features cannot be determined from TEM observations alone, we propose that both large self-interstitial loops, trapped at impurities within the material, and small, spherical nanovoids form.

Time-dependent neutronics in structural materials of inertial fusion reactors and simulation of defect accumulation in pulsed Fe and SiC

New results are presented on the time-dependent neutron intensities and energy spectra from compressed inertial fusion energy (IFE) targets and in structural Fe walls behind typical IFE chamber protection schemes. Protection schemes of LiPb and Flibe have been considered with two different thicknesses, and neutron fluxes in the outer Fe layer as a function of the time from target emission are given. Differences between the two solutions are noted and explained, and the effect of thickness is quantitatively shown. Time-dependent defect characterization of the Fe layer under pulse irradiation is presented. A new well-established multiscale modeling procedure injects, at the appropriate dose rate, damage cascades in a kinetic Monte Carlo lattice (microscopic) to study defect diffusion, clustering, and disintegration. The differences with a continuous irradiation for a still low fluence of irradiation are presented. Experimental validation of a multiscale modeling approach has been recognized and proposed in the Spanish VENUS-II project by using Fe ions on pure and ultrapure Fe. To study similar problems in SiC, new tools are needed to quantify the kinetic defects; results leading to the validation of a new tight binding molecular dynamics code for SiC are presented.

Recent theoretical and experimental results on inertial fusion energy physics

We study with ARWEN code a target design for ICF based on jet production. ARWEN is 2D Adaptive Mesh Refinement fluid dynamic and multigroup radiation transport. We are designing, by using also ARWEN, a target for laboratory simulation of astrophysical phenomena. We feature an experimental device to reproduce collisions of two shock waves, scaled to roughly represent cosmic supernova remnants. ANALOP code uses parametric potentials fitting to self-consistent potentials, it includes temperature and density effects by linearized Debye-Huckel and it treats excited configurations and H+He-like lines. Other is an average SHM using the parametric potentials above described. H-like emissivities and opacities have been simulated, using both, for Al and F plasmas with density 1023 cm-3 and temperatures higher than 200 eV. Advanced fusion cycles, as the aneutronic proton-boron 11 reaction, require very high ignition temperatures. Plasma conditions for a fusion-burning wave to propagate at such temperatures are rather extreme and complex, because of the overlapping effects of the main energy transport mechanisms. Calculations on the most appropriate ICF regimes for this purpose are presented. A new Monte Carlo procedure estimates effect of activation cross section uncertainties in the accuracy of inventory calculations, based on simultaneous random sampling of all the cross sections; it is implemented in activation code ACAB. We apply, with LLNL, to NIF gunite chamber shielding with reference pulsing operation. Preliminary results show that the 95 percentile of the distribution of the relative error of the contact dose rate can take values up to 1.2. Model is promising for uncertainty analysis of pulsed activation in IFE PP by using a continuous-pulsed model. Neutron intensities versus time after target emission are presented for IFE protections: LiPb/Flibe, including spectral effects. HT evaluation indicates that 90-98% of the total dose comes from ingestion of agriculture and meat, and the rest from inhalation by re-emission. A multiscale modeling (MM) study of pulse irradiation in Fe is presented up to microscopy; we give differences with continuous irradiation. Experimental validation of MM, using Fe+ in Fe, is being performed under VENUS II Spanish project with CIEMAT. Multiscale Modeling of SiC is reported; new defects energetic emerge using a new tight-binding molecular dynamics which has been proved in basic crystal parameters.

Insight into the materials choice for inertial fusion energy reactors considering radiation damage: Neutron irradiation intensities and basic knowledge from multiscale modeling

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.