[en] The electronic structure, magnetic and half-metallic properties of transitional metal (TM)-alloyed zinc-blende ZnO and GaAs (TM = Cr, Mn, Fe, Co, Ni) thin films with biaxial strains on the (0 0 1) plane are studied by density functional theory and beyond. Here, we focus on two simple layer-by-layer delta doping structures with the TM substituting along the (1 0 0) planes (type-I) and (0 0 1) planes (type-II). We find that the Fe-, Co- and Ni-alloyed GaAs, Mn- and Fe-alloyed ZnO, and Co-alloyed ZnO(II) show antiferromagnetic (AFM) states, while Ni-alloyed ZnO(I) and Cr-alloyed GaAs show ferromagnetic (FM) coupling independent of the biaxial strain within 25% along the (0 0 1) plane. For the systems of Cr-alloyed ZnO, Co-alloyed ZnO(I), Ni-alloyed ZnO(II) and Mn-alloyed GaAs(I, II), the strain from the substrate will induce a phase transition from AFM to FM states. The Co-alloyed ZnO(I), Ni-alloyed ZnO(I, II) and Cr-alloyed GaAs(I, II) systems are demonstrated to be half-metallic from the generalized gradient approximation (GGA) calculations. The Cr-alloyed ZnO and Mn-alloyed GaAs systems also show robust half-metallicity with a large spin-flip gap by a GGA + U description, although their half-metallicity disappears with the standard GGA description.

[en] Fuel performance, as well as fission and activation product behavior have been widely studied in high temperature gas-cooled reactors (HTGRs) since they directly influence reactor safety during normal operation and affect the radiological release during accidents. The key achievements of fuel performance in HTGRs include the design, improvement, and development of tristructural isotropic (TRISO)-coated fuel particle, which contains a central fuel kernel with four subsequent layers on the outside. The level of defective coated particles in the fuel elements in modern HTGRs has been testified to be very low. However, the diffusion of fission products from intact TRISO coated particles and/or defective coated particles, the fissile reactions of heavy metals contamination in the matrix graphite, and the activation reaction of impurities in the graphite and primary coolant are the three important generation sources of radioactive nuclides in HTGRs. In this paper, we present recent research progress on the fuel performance assessment in HTGRs, gather the experimental data about diffusion of typical metallic radioactive nuclides from various reactors and experiments, review the theoretical models to describe the transport behavior of metallic fission products, and analyze their fundamental characteristics. Finally, we summarize the recent and ongoing research on the transport behavior of typical nuclides (silver, etc.) and put forward relevant issues which are worth for further study. (author)