A multi-scale model for stresses, strains and swelling of reactor components under irradiation

Predicting strains, stresses and swelling in nuclear power plant components exposed to irradiation directly from the observed or computed defect and dislocation microstructure is a fundamental problem of fusion power plant design that has so far eluded a practical solution. We develop a model, free from parameters not accessible to direct evaluation or observation, that is able to provide estimates for irradiation-induced stresses and strains on a macroscopic scale, using information about the distribution of radiation defects produced by high-energy neutrons in the microstructure of materials. The model exploits the fact that elasticity equations involve no characteristic spatial scale, and hence admit a mathematical treatment that is an extension to that developed for the evaluation of elastic fields of defects on the nanoscale. In the analysis given below we use, as input, the radiation defect structure data derived from ab initio density functional calculations and large-scale molecular dynamics simulations of high-energy collision cascades. We show that strains, stresses and swelling can be evaluated using either integral equations, where the source function is given by the density of relaxation volumes of defects, or they can be computed from heterogeneous partial differential equations for the components of the stress tensor, where the density of body forces is proportional to the gradient of the density of relaxation volumes of defects. We perform a case study where strains and stresses are evaluated analytically and exactly, and develop a general finite element method implementation of the method, applicable to a broad range of predictive simulations of strains and stresses induced by irradiation in materials and components of any geometry in fission or fusion nuclear power plants.Peer reviewe

Simulating electronically driven structural changes in silicon with two-temperature molecular dynamics

Radiation can drive the electrons in a material out of thermal equilibrium with the nuclei, producing hot, transient electronic states that modify the interatomic potential energy surface. We present a rigorous formulation of two-temperature molecular dynamics that can accommodate these electronic effects in the form of electronic-temperature-dependent force fields. Such a force field is presented for silicon, which has been constructed to reproduce the ab initio-derived thermodynamics of the diamond phase for electronic temperatures up to 2.5eV, as well as the structural dynamics observed experimentally under nonequilibrium conditions in the femtosecond regime. This includes nonthermal melting on a subpicosecond timescale to a liquidlike state for electronic temperatures above ∼1eV. The methods presented in this paper lay a rigorous foundation for the large-scale atomistic modeling of electronically driven structural dynamics with potential applications spanning the entire domain of radiation damage

Interatomic exchange coupling of BCC iron

We performed first-principle calculations on the exchange interaction (EI) between atoms in BCC-Fe strained volumetrically. Our results show that the volume-dependence of the EI deviates considerably from the Bethe-Slater curve. This behavior is discussed in terms of the on-site and/or inter-site direct exchange interactions between electrons.Comment: 22 pages, 7 figure

An update on genomic-guided therapies for pediatric solid tumors

YesCurrently, out of the 82 US FDA-approved targeted therapies for adult cancer treatments, only three are approved for use in children irrespective of their genomic status. Apart from leukemia, only a handful of genomic-based trials involving children with solid tumors are ongoing. Emerging genomic data for pediatric solid tumors may facilitate the development of precision medicine in pediatric patients. Here, we provide an up-to-date review of all reported genomic aberrations in the eight most common pediatric solid tumors with whole-exome sequencing or whole-genome sequencing data (from cBioPortal database, Pediatric Cancer Genome Project, Therapeutically Applicable Research to Generate Effective Treatments) and additional non-whole-exome sequencing studies. Potential druggable events are highlighted and discussed so as to facilitate preclinical and clinical research in this area.Seed Grant of Strategic Research Theme for Cancer, The University of Hong Kong of AKSC. VWY Lui is funded by the Research Grant Council, Hong Kong (#17114814, #17121616, General Research Fund; T12–401/13-R, Theme-based Research Scheme), and the Start-up Fund, School of Biomedical Sciences, Faculty of Medicine, The Chinese University of Hong Kong. W Piao is funded by the Faculty Postdoctoral Fellowship Scheme, Faculty of Medicine, the Chinese University of Hong Kong