• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.900-906
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• 2024

The Passively-Cooled Molten Salt Fast Reactor (PMFR) is one of the advanced design concepts of the Molten Salt Fast Reactor (MSFR) which utilizes a natural circulation for the primary loop and aims to attain a long-life operation without any means of fuel reprocessing. For an extended operation period, it is necessary to have enough fissile material, i.e., high excess reactivity, at the onset of operation. Since the PMFR is based on a fast neutron spectrum, direct implementation of a burnable absorber concept for the control of excess reactivity would be ineffective. Therefore, a localized moderator concept that encircles the active core has been envisioned for the PMFR which enables the effective utilization of a burnable absorber to achieve low reactivity swing and long-life operation. The modified PMFR design that incorporates a moderator and burnable absorber is presented, where depletion calculation is performed to estimate the reactor lifetime and reactivity swing to assess the feasibility of the proposed design. All the presented neutronic analysis has been conducted based on the Monte Carlo Serpent2 code with ENDF/B-VII.1 library.

• Bulletin of the Korean Chemical Society
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• v.29 no.6
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• pp.1269-1272
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• 2008

• 한국생물공학회:학술대회논문집
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• 2000.11a
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• pp.781-784
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• 2000

A combination of Poisson-Boltzman (PB) equation and quantum mechanics methodologies has been used for the calculation of the solvation energies and $pK_a$ values of biomolecules such as amino acids and nucleotide bases.

• Nuclear Engineering and Technology
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• v.41 no.7
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• pp.875-884
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• 2009

We present three nuclear/hydrogen-related R&D activities being performed at KAIST: air-ingressed LOCA analysis code development, gas turbine analysis tool development, and hydrogen-production system analysis model development. The ICE numerical technique widely used for the safety analysis of water-reactors is successfully implemented into GAMMA, with which we solve the basic equations for continuity, momentum conservation, energy conservation of the gas mixture, and mass conservation of 6 species (He, N2, O2, CO, CO2, and H2O). GAMMA has been extensively validated using data from 14 test facilities. We developed a tool to predict the characteristics of HTGR helium turbines based on the throughflow calculation with a Newton-Raphson method that overcomes the weakness of the conventional method based on the successive iteration scheme. It is found that the current method reaches stable and quick convergence even under the off-normal condition with the same degree of accuracy. The dynamic equations for the distillation column of HI process are described with 4 material components involved in the HI process: H2O, HI, I2, H2. For the HI process we improved the Neumann model based on the NRTL (Non-Random Two-Liquid) model. The improved Neumann model predicted a total pressure with 8.6% maximum relative deviation from the data and 2.5% mean relative deviation, and liquid-liquid-separation with 9.52% maximum relative deviation from the data.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.12
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• pp.767-775
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• 2014

New material design has obtained tremendous attention in material science community as the performance of new materials, especially in nano length scale, could be greatly improved to applied in modern industry. In certain conditions limiting experimental synthesis of these new materials, new approach by computer simulation has been proposed to be applied, being able to save time and cost. Recent development of computer systems with high speed, large memory, and parallel algorithms enables to analyze individual atoms using first principle calculation to predict quantum phenomena. Beyond the quantum level calculations, mesoscopic scale and continuum limit can be addressed either individually or together as a multi-scale approach. In this article, we introduced current endeavors on material design using analytical theory and computer simulations in multi-length scales and on multi-physical properties. Some of the physical phenomena was shown to be interconnected via a cross-link rule called 'cross-property relation'. It is suggested that the computer simulation approach by multi-physics analysis can be efficiently applied to design new materials for multi-functional characteristics.

• Nuclear Engineering and Technology
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• v.50 no.3
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• pp.327-339
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• 2018

This article presents a new global-local hybrid coarse-mesh finite difference (HCMFD) method for efficient parallel calculation of pin-by-pin heterogeneous core analysis. In the HCMFD method, the one-node coarse-mesh finite difference (CMFD) scheme is combined with a nodal expansion method (NEM)-based two-node CMFD method in a nonlinear way. In the global-local HCMFD algorithm, the global problem is a coarse-mesh eigenvalue problem, whereas the local problems are fixed source problems with boundary conditions of incoming partial current, and they can be solved in parallel. The global problem is formulated by one-node CMFD, in which two correction factors on an interface are introduced to preserve both the surface-average flux and the net current. Meanwhile, for accurate and efficient pin-wise core analysis, the local problem is solved by the conventional NEM-based two-node CMFD method. We investigated the numerical characteristics of the HCMFD method for a few benchmark problems and compared them with the conventional two-node NEM-based CMFD algorithm. In this study, the HCMFD algorithm was also parallelized with the OpenMP parallel interface, and its numerical performances were evaluated for several benchmarks.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.2
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• pp.1563-1570
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• 2015

Conformational change during chain propagation of alanine oligomer was investigated by quantum chemical calculation(QCC) using 2~5mers(${\times}=2{\sim}5$) models. For estimation of the end group effects, two types of end group. "amide type" ($CH_3CONH-and-CONHCH_3$) and "methyl type" ($CH_3CONH-and-CONHCH_3$), were prepared as both ends(N-and-C). Conformers optimized for 5-mer converged to three types of ${\Phi}/{\Psi}$ : ${\alpha}$-helix(g+/g+, or g-/g-), PPII-like(extended helix-like, g+/g-, or g-/g+), and ${\beta}$-extended (t+/t-, or t-/t+), in the order of lower energy, and the energies of left- and right- handed conformers were the same (5-mer. amide type ${\Delta}E=-1.05$, right type ${\Delta}E=-1.62$). Energies of the monomer unit(${\Delta}E$) of ${\alpha}$-helix decreased with increases of monomer.

• Journal of the Korean Chemical Society
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• v.3 no.1
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• pp.3-8
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• 1954

Fowler obtained thermodynamic quantities assuming the theory which could be derived by representing the system with microcanonical ensemble, in order to introduce the temperature T of the system proper, he considered the combined systems which are composed of the system proper and another arbitrary system that is in thermal contact with the former, and represented the combined system by a microcanonical ensemble, here, he used the steepest descent method in his calculation. This Fowler's treatment is not only unsatisfactory at the point of theoretical view but also he could not make the formulation of free energy of Helmholtz's so that this formular was forced to be assumed. From the point of Quantum Statistical Mechanical view, the materially closed system which is in an equilibrium state with the temperature T is best represented by canonical ensemble. At the actual derivation of the distribution law and thermodynamic quantities, however, in order to avoid the difficulty of calculation Tolman proceeded his calculation either representing the system proper by the grand-canonical ensemble or adding a certain limitation.

• Bulletin of the Korean Chemical Society
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• v.32 no.7
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• pp.2301-2305
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• 2011

The potential energy surface (PES) for the loss of HCN or HNC from the pyrazine molecular ion was determined based on quantum chemical calculations using the G3//B3LYP method. Four possible dissociation pathways to form four $C_3H_3N^{+{{\bullet}}$ isomers were examined. A Rice-Ramsperger-Kassel-Marcus quasi-equilibrium theory model calculation was performed to predict the dissociation rate constant and the product branching ratio on the basis of the obtained PES. The resultant rate constant for the HCN loss agreed with the previous experimental result. The kinetic analysis predicted that the formation of $CH=CHN{\equiv}CH^{+{\bullet}}+HCN$ was predominant, which occurred by three consecutive steps, a C-C bond cleavage to form a linear intermediate, a rearrangement to form an H-bridged intermediate, and elimination of HCN.

• Journal of Magnetics
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• v.22 no.1
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• pp.1-6
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• 2017

Magnetic properties of CoPt nanoparticles (average size = 2.1 nm) encapsulated in synthesized protein shell have been investigated with SQUID (Superconducting Quantum Interference Device) magnetometer and analyzed by the recently developed non-equilibrium magnetization calculation by our group [T. H. Lee et al., Phys. Rev. B 90, 184411 (2014)]. Field dependence of magnetization measured at 2 K was successfully analyzed with modified Langevin function. In addition, small hysteresis loops having the coercive field of 890 Oe were observed at 2 K. Temperature dependence of magnetization has been measured with zero field cooled (ZFC) and field cooled (FC) protocol with slightly modified sequence in accordance with non-equilibrium magnetization calculation. The analysis on the M vs. T data revealed that the anisotropy energy barrier distribution is found to be very different from the log-normal distribution found in a size distribution. Zero temperature coercive field and Bloch coefficient have also been extracted from the analysis and the validity of those values is checked.