Helmholtz-Zentrum Dresden-Rossendorf e. V.

The coupled code system DYN3D/ATHLET is continuously developed and validated for transient analyses of sodium-cooled fast reactors (SFRs).In this study, the system was applied to model the loss of flow without scram (LOFWOS) test conducted at the Fast Flux Test Facility (FFTF), with the aim of further assessing the coupled 3D neutronics and system-level thermal hydraulics anal. capabilities.Two simulation approaches were employed.The first approach utilized the point kinetics module of ATHLET for neutron physics.The second relied on the 3D spatial kinetics solver of DYN3D.In both cases, the thermal hydraulics of the system was handled by ATHLET, while neutronics data was generated by the Serpent Monte Carlo code.The performance of both approaches was evaluated by comparing their results with exptl. data.Addnl., the feasibility of using the adaptive decay heat model, a recent enhancement in DYN3D, was demonstrated.This paper concludes the FFTF LOFWOS study, extending the validation base for the DYN3D/ATHLET system in comprehensive SFR modeling.

Janus SeMoS monolayers (MLs) are synthetic 2D materials with unique electronic properties, as theory predicts, but their experimental exploration has been hindered by the low quality of the samples. Here we report a synthesis of high-quality Janus MLs on gold substrates by thermal exchange reaction taking place at the ML/Au(111) interface. The synthesized Janus SeMoS MLs were characterized by complementary techniques, and insights into the topography and electronic properties of the system were obtained. Specifically, due to the lattice mismatch with the Au(111), a moiré pattern with a periodicity of 2.9 nm was observed. A precise experimental determination of the lattice constant of Janus SeMoS of 3.22 ± 0.01 Å was obtained, and the measured spin-orbit splitting at the K point of the valence band was found to be 170 ± 15 meV, matching well the results of the density functional theory calculations.

Heavier transition metal carbyne analogs hold significant potential for cooperative activation of small molecules. However, complexes containing more than one heavier tetrylidyne ligand RE (E = Si, Ge, Sn, Pb) are rare due to the high oligomerization tendency of RE ligands. In this study, we describe the complex [Fe(SnAr')₂] (1; Ar' = 2,6-Dipp₂-C₆H₃, Dipp = 2,6-ⁱPr₂-C₆H₃), which features adjacent Fe-Sn single and double bonds. Complex 1 exhibits versatile reactivity with transition metal and main group compounds. Treatment of complex 1 with Ni(COD)₂ (COD = 1,5-cyclooctadiene) yields the tetranuclear complex [Fe(μ-SnAr')₂Ni] (2), characterized by an unusual "push-pull" interaction between nickel(0) and the two coordinating Sn atoms, as revealed by quantum chemical studies. The reaction of complex 1 with AlBr₃ results in Al-Br bond cleavage and Ar' migration to aluminum. CH₃I adds oxidatively to the Sn atom that is singly bonded to Fe, while PMe₃ coordinates to Fe, inducing reversible cleavage of the Fe═Sn double bond. In addition, complex 1 activates inorganic molecules. CO₂ undergoes disproportionation to produce a carbonate-bridged Ar'Sn(μ-OCO₂)SnAr' ligand, whereas CS₂ is reductively coupled to form an ethylene tetrathiolate ligand ([C₂S₄]^4-). The reaction with white phosphorus (P₄) generates an unusual Ar'P₄Sn₂Ar' ligand. This multifaceted reactivity illustrates the behavior of the Fe and Sn sites in complex 1, suggesting that complexes of this type are promising reagents for small molecule activation.