Primary radiation damage : A review of current understanding and models

Scientific understanding of any kind of radiation effects starts from the primary damage, i.e. the defects that are produced right after an initial atomic displacement event initiated by a high-energy particle. In this Review, we consider the extensive experimental and computer simulation studies that have been performed over the past several decades on what the nature of the primary damage is. We review both the production of crystallographic or topological defects in materials as well as radiation mixing, i.e. the process where atoms in perfect crystallographic positions exchange positions with other ones in non-defective positions. All classes of materials except biological materials are considered. We also consider the recent effort to provide alternatives to the current international standard for quantifying this energetic particle damage, the Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model for metals. We present in detail new complementary displacement production estimators ("athermal recombination corrected dpa", arc-dpa) and atomic mixing ("replacements per atom", rpa) functions that extend the NRT-dpa, and discuss their advantages and limitations. (C) 2018 The Authors. Published by Elsevier B.V.Peer reviewe

Materials R&D for a timely DEMO: Key findings and recommendationsof the EU Roadmap Materials Assessment Group

The findings of the EU Fusion Programme’s ‘Materials Assessment Group’ (MAG), assessing readiness ofStructural, Plasma Facing (PF) and High Heat Flux (HHF) materials for DEMO, are discussed. These areincorporated into the EU Fusion Power Roadmap [1], with a decision to construct DEMO in the early2030s.The methodology uses project-based and systems-engineering approaches, the concept of TechnologyReadiness Levels, and considers lessons learned from Fission reactor material development. ‘Baseline’materials are identified for each DEMO role, and the DEMO mission risks analysed from the known lim-itations, or unknown properties, associated with each baseline material. R&D programmes to addressthese risks are developed. The DEMO assessed has a phase I with a ‘starter blanket’: the blanket mustwithstand @le;2 MW yr m−2fusion neutron flux (equivalent to ∼20 dpa front-wall steel damage). The base-line materials all have significant associated risks, so development of ‘Risk Mitigation Materials’ (RMM)is recommended. The R&D programme has parallel development of the baseline and RMM, up to ‘down-selection’ points to align with decisions on the DEMO blanket and divertor engineering definition. ITERlicensing experience is used to refine the issues for materials nuclear testing, and arguments are devel-oped to optimise scope of materials tests with fusion neutron (‘14 MeV’) spectra before DEMO designfinalisation. Some 14 MeV testing is still essential, and the Roadmap requires deployment of a ≥30 dpa(steels) testing capability by 2026. Programme optimisation by the pre-testing with fission neutronson isotopically- or chemically-doped steels and with ion-beams is discussed along with the minimum14 MeV testing programme, and the key role which fundamental and mission-oriented modelling canplay in orienting the research

Radiation-Induced Effects on Microstructure

Irradiation of materials with particles that are sufficiently energetic to create atomic displacements can induce significant microstructural alteration, ranging from crystalline-to-amorphous phase transitions to the generation of large concentrations of point defect or solute aggregates in crystalline lattices. These microstructural changes typically cause significant changes in the physical and mechanical properties of the irradiated material. A variety of advanced microstructural characterization tools are available to examine the microstructural changes induced by particle irradiation, including electron microscopy, atom probe field ion microscopy, X-ray scattering and spectrometry, Rutherford backscattering spectrometry, nuclear reaction analysis, and neutron scattering and spectrometry. Numerous reviews, which summarize the microstructural changes in materials associated with electron and heavy ion or neutron irradiation, have been published. These reviews have focused on pure metals as well as model alloys, steels, and ceramic materials. In this chapter, the commonly observed defect cluster morphologies produced by particle irradiation are summarized and an overview is presented on some of the key physical parameters that have a major influence on microstructural evolution of irradiated materials. The relationship between microstructural changes and evolution of physical and mechanical properties is then summarized, with particular emphasis on eight key radiation-induced property degradation phenomena. Typical examples of irradiated microstructures of metals and ceramic materials are presented. Radiation-induced changes in the microstructure of organic materials such as polymers are not discussed in this overview

A set of MATLAB routines and associated files for prediction of radiation-enhanced diffusion in ion irradiated materials

This article presents MATLAB routines that may be used to evaluate radiation-enhanced diffusion (RED) in ion irradiation materials. Four routines are included: Main, DataCollect, Diffuse, and Directory. A sample input file and README are also included. The input may be directly modified as provided and used as an input to the routines. Data from Stopping Range of Ions in Matter (SRIM) is also required as an input. A stream of data files at different damage conditions is created by the routines

Helium causing disappearance of a/2<111> dislocation loops in binary Fe-Cr ferritic alloys

International audienceSingle and dual-beam self-ion irradiations were performed at 500°C on ultra-high purity Fe14%Cr alloy to ∼0.33 displacements-per-atom (dpa), and 0 or 3030 atomic-parts-per-million (appm) helium/dpa, respectively. Using transmission electron microscopy, we reveal that helium can drastically modify the dislocation loop Burgers vector in Fe-Cr alloys. Helium co-implantation caused complete disappearance of a/2 type dislocation loops, and the microstructure consisted of only a loops. Conversely, a/2 type loops were predominant without He co-implantation. The total loop density remained largely unaffected. The results strikingly contrast literature asserting that helium stabilizes a/2 type loops in bcc Fe alloys, based on low temperature irradiations. Collectively analyzing the results with literature suggest that the small positive interaction between helium and self-interstitial atoms (SIA) in Fe predicted by atomistic simulations maybe insufficient to holistically explain the dislocation loop microstructure development in presence of helium. Helium-SIA positive binding inadvertently implies elevated a/2 loop fraction and higher loop densities that the present results contradict. Helium induced high cavity density causing a preferential loss of highly glissile clusters, leaving the matrix saturated with type clusters is proposed as a potential mechanism. Further, the in-situ irradiations combined with Burgers vector analysis strengthened the evidence of Cr-induced dislocation loop mobility reduction that appears to stabilize the a/2 type loops and causes higher loop densities in Fe-Cr alloys