Implementation of high-fidelity neutronics and thermal–hydraulic coupling calculations in HNET

To perform nuclear reactor simulations in a more realistic manner,the coupling scheme between neutronics and thermal-hydraulics was implemented in the HNET program for both steady-state and transient conditions.For simplicity,efficiency,and robustness,the matrixfree Newton/Krylov(MFNK)method was applied to the steady-state coupling calculation.In addition,the optimal perturbation size was adopted to further improve the convergence behavior of the MFNK.For the transient coupling simulation,the operator splitting method with a staggered time mesh was utilized to balance the computational cost and accuracy.Finally,VERA Problem 6 with power and boron perturbation and the NEACRP transient benchmark were simulated for analysis.The numerical results show that the MFNK method can outperform Picard iteration in terms of both efficiency and robustness for a wide range of problems.Furthermore,the reasonable agreement between the simulation results and the reference results for the NEACRP transient benchmark verifies the capability of predicting the behavior of the nuclear reactor.

Close coupling calculations for excitation partial cross sections in Ne-HF collisions

This paper reports that an exact quantum close coupling calculation is carried out for rotational excitation in Ne HF collisions on the available anisotropic potential. Partial cross sections are obtained separately at the incident energies of 48.35, 75, 120 and 150meV. The reliability of the results is demonstrated by comparison with previously published theoretical findings. Based on the calculations, the effect of the potential energy surface on the excitation partial cross sections is discussed in detail.

A high fidelity general purpose 3-D Monte Carlo particle transport program JMCT3.0

JMCT is a large-scale,high-fidelity,three-dimensional general neutron–photon–electron–proton transport Monte Carlo software system.It was developed based on the combinatorial geometry parallel infrastructure JCOGIN and the adaptive structured mesh infrastructure JASMIN.JMCT is equipped with CAD modeling and visualizes the image output.It supports the geometry of the body and the structured/unstructured mesh.JMCT has most functions,variance reduction techniques,and tallies of the traditional Monte Carlo particle transport codes.Two energy models,multi-group and continuous,are provided.In recent years,some new functions and algorithms have been developed,such as Doppler broadening on-thefly(OTF),uniform tally density(UTD),consistent adjoint driven importance sampling(CADIS),fast criticality search of boron concentration(FCSBC)domain decomposition(DD),adaptive control rod moving(ACRM),and random geometry(RG)etc.The JMCT is also coupled with the discrete ordinate SNcode JSNT to generate source-biasing factors and weight-window parameters.At present,the number of geometric bodies,materials,tallies,depletion zones,and parallel processors are sufficiently large to simulate extremely complicated device problems.JMCT can be used to simulate reactor physics,criticality safety analysis,radiation shielding,detector response,nuclear well logging,and dosimetry calculations etc.In particular,JMCT can be coupled with depletion and thermal-hydraulics for the simulation of reactor nuclear-hot feedback effects.This paper describes the progress in advanced modeling,high-performance numerical simulation of particle transport,multiphysics coupled calculations,and large-scale parallel computing.

Structural,electronic,and magnetic properties of vanadium atom-adsorbed MoSe2 monolayer

Using the first-principles calculations, we study the structural, electronic, and magnetic properties of vanadium adsorbed MoSe_2 monolayer, and the magnetic couplings between the V adatoms at different adsorption concentrations. The calculations show that the V atom is chemically adsorbed on the MoSe_2 monolayer and prefers the location on the top of an Mo atom surrounded by three nearest-neighbor Se atoms. The interatomic electron transfer from the V to the nearestneighbor Se results in the polarized covalent bond with weak covalency, associated with the hybridizations of V with Se and Mo. The V adatom induces local impurity states in the middle of the band gap of pristine MoSe_2, and the peak of density of states right below the Fermi energy is associated with the V- dz^2 orbital. A single V adatom induces a magnetic moment of 5 μBthat mainly distributes on the V-3d and Mo-4d orbitals. The V adatom is in high-spin state, and its local magnetic moment is associated with the mid-gap impurity states that are mainly from the V-3d orbitals. In addition,the crystal field squashes a part of the V-4s electrons into the V-3d orbitals, which enhances the local magnetic moment.The magnetic ground states at different adsorption concentrations are calculated by generalized gradient approximations（GGA） and GGA＋U with enhanced electron localization. In addition, the exchange integrals between the nearest-neighbor V adatoms at different adsorption concentrations are calculated by fitting the first-principle total energies of ferromagnetic（FM） and antiferromagnetic（AFM） states to the Heisenberg model. The calculations with GGA show that there is a transition from ferromagnetic to antiferromagnetic ground state with increasing the distance between the V adatoms. We propose an exchange mechanism based on the on-site exchange on Mo and the hybridization between Mo and V, to explain the strong ferromagnetic coupling at a short distance between the V adatoms. However, the ferromagnetic exchange mechanism is sensitive to both the increased inter-adatom distance at low concentration and the enhanced electron localization by GGA＋U, which leads to antiferromagnetic ground state, where the antiferromagnetic superexchange is dominant.

Estimation of solid concentration in solid-liquid two-phase flow in horizontal pipeline using inverse-problem approach

In this study,an inverse-problem method was applied to estimate the solid concentration in a solid-liquid two-phase flow.An algebraic slip mixture model was introduced to solve the forward problem of solid-liquid convective heat transfer.The time-average conservation equations of mass,momentum,energy,as well as the volume fraction equation were computed in a computational fluid dynamics(CFD)simulation.The solid concentration in the CFD model was controlled using an external program that included the inversion iteration,and an optimal estimation was performed via experimental measurements.Experiments using a fly-ash-water mixture and sand-water mixture with different solid concentrations in a horizontal pipeline were conducted to verify the accuracy of the inverse-problem method.The estimated results were rectified using a method based on the relationship between the estimated results and estimation error;consequently,the accuracy of the corrected inversion results improved significantly.After a verification through experiments,the inverse-problem method was concluded to be feasible for predicting the solid concentration,as the estimation error of the corrected results was within 7%for all experimental samples for a solid concentration of less than 50%.The inverse-problem method is expected to provide accurate predictions of the solid concentration in solid-liquid two-phase flow systems.

Numerical Simulation of Induced Alterations of Flow Patterns Within Glass Melts using External Lorentz Forces

A common way to produce glass is to use melting tanks that work continually with several hundred tons per day.The process of efficiently melting,refining,and homogenizing the glass melt is strongly dependent on the flow patterns within the melting tank.In order to improve the quality of glass products and the efficiency of the melting process,it is necessary to control the flow patterns and to optimize the temperature distribution within the melting tank.Using Lorentz force to create additional flow components based on electric current density distributions and externally generated magnetic fields is an excellent method to obtain targeted and tailored flow influences.In order to evaluate this method,it is necessary to simulate the induced alterations of the melt flow.Such numerical simulations require the coupling of the electromagnetic and flow field calculations including the energy equation because the electrical conductivity of the molten glass is strongly dependent on the temperature.The idea is to include the calculation of the magnetic field completely into FLUENT using the so-called User Defined Scalars(UDS)and User Defined Functions(UDF).